Raising Primula From Seed

The First APS Round Table
"Raising Primula From Seed"
by Richard Critz, Rosemont, PA
(Reprinted, with edits, from the Summer 1985 issue of Primroses)

RLC: Good evening ladies and gentlemen and welcome to our round table on seeding methods for primula. We all appreciate your willingness to share, we really do, and look forward a little later to your words of wisdom. But before introducing our impressive panel of experts I’d like to take just a few moments to tell both you and our audience why we are here just now and what we would like to accomplish.

The genus Primula contains more than 500 species, and a much larger number of hybrids. All species can be raised from seed (if available) and even many of the hybrids come true with sufficient regularity to make seeding a worthwhile method. To those who decide for the first time to experience the satisfaction of raising primula from seed, it is confusing to discover that hardly any two growers agree on the proper ‘modus operandi.’ In such matters as seeding mixture, size and type of containers, pre-treatment of seed, time for planting, and many other details of the process there are wide differences of practice. One very successful grower of lovely primula once said right out loud, “Bosh! I just sow my seed out under an apple tree and let it grow.” Another wrote me recently, “After more than 30 years of growing from seed I have developed a system that works for me with very little care after planting. I need that. But there are as many different methods as there are people who grow primula from seed. If you find a system that works for you, stick with it.”

Now I know and you know that a million articles have appeared on the subject of primula seeding. But as Editor of this Journal I still get requests for information on this subject - numerous requests. Hence our Round Table, an attempt to bring together the practices and opinions of our best growers. While it is doubtless true that a book could be written about the specific requirements of each species, we hope that what follows will enable every grower - especially the new grower - to devise a step-by-step procedure for him or her self that not only fits the particular conditions under which (s)he works, but will insure reasonable success with this large and varied plant genus. Along the way we will try to pick up significant variations for specific species - exceptional soil needs, time of sowing, temperature requirements, and so on. Is your game plan clear, distinguished panel?

If so, may we proceed to introduce our guests. Mr. Joe Kennedy hails from Ballycastle in County Antrim, Northern Ireland. His interest is in breeding primulas. He does about 150 crosses a year and grows-on a thousand resulting seedlings to flowering. Rosetta Jones lives and works with her husband Alan in Kent, WA. The Jones’ are specialists in double acaulis, which they hybridize and raise at their small nursery. Rosetta has done considerable study in genetics and brings a keen understanding of what is happening to her work. Needless to say, her plants are beautiful. Florence Bellis is one of the great ones in American horticulture. Her important hybridizing program at Barnhaven, near Portland, OR, begun in the 1930s, resulted in a new race of hardy and beautiful polyanthus, created a deep and abiding interest in the U.S.A. for the genus Primula, and resulted - through her writing - in the formation of the American Primrose Society in the early 1940’s. Anita Alexander, a past president of the APS and former Editor of the Journal, lives with her husband in Boring, OR, where she has been hybridizing candelabra primulas (Section Proliferae) for 30 years. Bernard Smith lives in Kent about 25 miles south of London. He is one of those fantastic English gardeners who have spent a lifetime “in trade” as they say, but have developed and honed a hobby to near perfection.
William Holt, from Ayrshire in Scotland, has known and loved primula for a lifetime, and has worked among them every day. His interests culminated some ten years ago in an intense interest in the cultivated forms of primroses (acaulis) and polyanthus.
Steven John Kelley is a young man from Long Lake, a small town in MN. about 20 miles west of Minneapolis. He has been interested in plants from childhood, and, together with his father, operates a small nursery and family business, which boasts extensive display gardens. Herbert Dickson owns and operates the Chehalis Rare Plant Nursery 50 miles south of Tacoma. Primula is the business of CRPN, and of the many kinds grown, the auricula is king. In fact, Herb has spent much of his life developing remarkable and beautiful garden auricula. I am sure that nowhere else in the world could so many and such lovely kinds be found. He sells not only plants, but seed.

Procuring Good Seed

RLC: OK, panel. let’s turn to our first consideration. Where do you obtain good seed, and how can you be sure it’s “good?”

Joe Kennedy: “Most of the seed I sow comes from my own crosses, but I do get seed of species from the seed lists of the Alpine Garden Society in England, the Scottish Rock Garden Club, and of course, the APS.”

Rosetta Jones: “Some commercial sources could be mentioned too: Ghose and Kholi in India, Jack Drake in Scotland, Chiltern and Barnhaven in England, and there are many others.

Florence Bellis: “It is advisable to order seed early from a reputable dealer, whoever that might be.”

Anita Alexander: “Yes. You have to be careful. The seed from many exchanges and some commercial sources are not true to name.”

Bernard Smith: “ I don’t recommend seed from seed merchants, but try if possible to get seed from fellow society members who often have a pinch to spare.”

RLC: “How can you tell if the seed you get is good?”

Joe K: “Most primula seed is, mercifully, large enough to deal with easily. Seed of species like P. flaccida, capitata and some of the Farinosae is very fine and tends to hide amongst the chaff and farina. But when rolled between finger and thumb this fine seed has a filmy or slippery feeling, and can be detected even amongst chaff and farina. Good seed is usually fat and slippery.”

Rosetta: “If I’m in doubt whether seed is real or chaff, the use of a good magnifying glass usually settles it.”

Florence: “In the 1930s when I became a seed specialist the behavior of seed was as yet little known. At that time primrose seed was notoriously difficult to germinate - a year’s wait for a spotty emergence was not unusual. Garden writers, who knew nothing about seed, poured out many positive words on the subject of viability. They had no way of knowing that poor germination, or outright failure, was not the fault of the seed, but the seed men’s improper picking and storing of it. Many growers unwittingly picked green seed along with the ripe, and no immature seed will germinate. Some believed that poor germination increased sales, and some were actually accused of drying their crop in the oven to insure a percentage of loss Certainly no one I knew stored their seed, after careful picking, curing and shelling, in airtight containers at low temperatures. Well, starting from there I soon learned that full germination could be brought about in a matter of weeks if the seed had been properly picked, handled and stored, airtight, at around 40 degrees F. You know, plant conception is remarkably like our own. For most plants, including primula, it usually takes place in a day, between the rising and setting of the sun.”

Storing The Seed

RLC: I noticed that you mentioned storing the seed. Anyone have ideas on that?

Bernard Smith: “I sow the seed as soon as possible. Primula seed is not long lived and any laying around in high heat and humidity can reduce its viability still further. As a rule I try to sow seed within the year of collecting.”

Joe Kennedy: “I sow primula seed immediately, regardless of the time of year. If I have to delay, I keep it refrigerated.”

William Holt: I find that seed collected and stored cool and dry can be kept until the following spring. On sowing it will germinate readily. The one exception seems to be the Petiolaris Section. With these species most growers say the seed should never be allowed to dry, but should be sown as soon as it is ripe, with germination following in a couple weeks. That any attempt to store this seed is almost sure to end in failure.”

Anita: “The petiolaris are a problem, Bill, and I’d like to add a word about another toughie - Primula rosea. I dry rosea seed about 4 days, then refrigerate it, cold but not frozen. (I never allow primula seed to freeze.) I just germinated P. rosea seed that was 3 years old! But I know that if I had let it sit around in a warm room for just a month it would be quite dead.”

RLC: The concensus then is that if seed cannot be sown at once it can be stored?

Florence: “Yes. Seed will live for years if kept cool, airtight and dry. place the packets in a tightly covered screw-top glass jar (glass does not draw moisture as plastic does), and store in the refrigerator, away from the freezing compartment. A quart jar holds many packets and takes little room in its corner where the temperature stays around 40 degrees F. Scientists now believe that low temperatures either destroy some chemical that inhibits germination, or generates one that stimulates it. This may be, but long experience has taught me that airtight, dry, cold storage prolongs the life of the embryo, and without that live embryo no seed can germinate.”

Steven Kelley: “Interesting, Florence, that you should say that. I remember an article once by Ralph Balcom in which he noted that some seed, including auricula, seem to require a resting period before planting. Scientists now believe that the encased embryo could survive indefinitely on the food stored for it were it not for protein deterioration and respiratory failure. When moisture, and warmth penetrate the seed coat before the seed is planted, the embryo responds as it would to normal germinating conditions and uses up the stores its mother packed for its first rooting and leafing. This can happen in a normal heated room. Consequently, when the seed is planted the food and oxygen have been used up and the infant is dead, or not enough remains to support it until it can root and support itself. The life of certain short-span seeds has been prolonged as much as 50 times their normal expectancy when kept dry and airless in cold storage. Long-lived seeds sleep safely for years.”

When To Plant

RLC: All of which brings us to the question of when to plant. What is the best time to plant primula seed?

Herb Dickson: “I start planting during January in the warm comfort of my heated basement. I do as many as I like of an evening, and then set them right out in the weather. The natural conditions seem to help germination, and when everything is right, the seeds come up.”

B. Smith: “As soon as my seed are ripe I harvest and plant. That’s usually in September .”

J. Kennedy: “Most of my seed is sown about this same time, although I have sown up into late November. This seed germinated very well indeed, in February. For me, spring sowing from the seed lists does not germinate nearly so well.”

W. Holt: “One cannot generalize over the whole primula range. But I sow vernales and others outdoors in July and August, and indoors from Christmas to the end of February, using bottom heat. This heat seems to give the process a boost, especially when the seed have been frozen during the winter.”

Anita: “I find it varies by sections. I try to consider the native habitat and what the plants do in nature. Most primulas ripen their seed in early summer and do best if sown soon after collecting, from early to mid summer. That way, plants big enough to withstand the winter will be produced before dormancy comes. With summer flowerers it’s best to keep the seed, cool and dry of course, for spring sowing. Any bought seed may be a year old and should be sown immediately. Lots of people recommend sowing as soon as seed is ripe, but except for a very few difficult species, this is not really necessary, and can be downright detrimental to good germination. I remind you all of Florence’s statement that a dormant period may produce germination-enhancing chemical changes. Often, storing seed dry until December, or even April, will lead to better results.

Rosetta: “Seed planted from January to March will produce good plants by fall and flower the following year. Fresh doubles seed do well at this time, but I understand that in a warm climate these do better if sowed earlier, say October through February.”
Kelley: “Like Anita I like to think of the normal cycle in the wild. While I have planted in both fall and spring with nearly equal success, I note that published research suggests that many seeds need a cold period before they will germinate. You know, successive freezing and thawing.”

RLC: Heavens, we have some diversity here! On the strength of what we’ve heard would it be safe to say that primula will germinate just about any time you put them in the ground?

RLC: I take it the rest of you are pretty much in agreement? No serious dissent?

Seedling Mixtures

Let’s move on then to the plant mix to be used in seeding. How many of you use soil-less mixes? Let’s have a show of hands. That’s just over half. And the rest of you use soil, I presume. Let’s hear from you soil-using people first.

Herb?: “First and most important, I start with a sterile medium. I used to bake small batches of soil in the oven and mix in peat, vermiculite and sand. As I grew more seed I acquired an electric sterilizer for my soil mix. Then, as I got older and lazier, and good prepared mixes became available, I used them and doctored with my own ingredients according to the species I was planting. My basic rooting mix is (roughly) 2 parts pumice, 2 parts sand, 2 parts garden loam and compost mixed, 1/2 part peat moss,1/2 part perlite. To this I often add enough lime to get a pH of 6 to 6.5, and some slow release fertilizer. The Primrose Society has published other seed mixes from time to time, most of which use soil. What they say basically is that any mix is good provided it is porous in texture and not too rich in plant food. One article says the medium should be “loose and friable so that water will drain through readily, yet retain enough to stay moist.” You can use anything you have to do this - leaf mold, compost, sand, peat moss, vermiculite, etc. in any combination that will give you the proper degree of friability. This may be tested by squeezing a handful of the moistened mixture and noting whether it falls apart when the pressure is released. Another good test is to fill a pot with the mixture, compress it moderately, and note whether water soaks through it rapidly and disappears from the surface within a few seconds. If not, it is wise to add extra course sand until it does. Then, of course, the soil mix should be sterilized. This is important.”

RLC: Thanks Herb. That’s clear and concise. And now, how about the situation in the British Isles? Joe?

Kennedy: “I find a well sifted mix of 1/3 each peat, sand and leaf mold makes a nice soft medium - friable. I use John Innes compost, a prepared seed mix for the Auricula Section at times, but it tends to ‘cake’ hard if left in the seed tray too long. Brian Halliwell at Kew and Jack Drake in Scotland recommend a seed compost like mine and Brian, too, stresses sterilization.”
RLC: How about hearing from the soil-less group now? Rosetta?

Rosetta: “It is important to use a sterile mix. I use a purchased mix called Reddi-Earth. It is peat, vermiculite, sphagnum, with some fertilizer in it, and it is sterile. I use Reddi-Earth for all my seeds - but others use Agway or Pro Mix, there are lots of them. Seed does not need fertilizer until it has produced roots as the seed endosperm furnishes the nutrients for the initial growth.”

Anita: “The seeding mix must provide 3 things, physical anchorage for the plant, air drainage and constant moisture. At present I’m using a commercial mix too, of peat and volcanic rock. For candelabras I like sifted loam instead of the commercial mix. I often go by the feel of the mix. It has to be loose and friable.”

RLC: What about in Britain? Bill.

Holt: “I use a soil-less compost mixture - 2 of peat, 2 sand, and 1 vermiculite, with Adrin or Gamma B. H. C. dust added. I never use anything but soil-less mix for seed sowing. The people at Chiltern Seed are pretty emphatic about this too. They say, “Without hesitation, we recommend that you sow all seed in a soil-less seed compost, not in soil. Whenever we have carried out comparative trials between the two the difference in germination has been quite remarkable. It’s worth the small extra cost.”

RLC: You must have something to say about all this Florence.

Florence: “I do, and thank you Richard. Properly picked and stored seed cannot help becoming healthy seedlings when air and water circulation is good, when there is a cool sun sweep and the seeding medium is not nutrient rich. A lean bed is appropriate for germinating seeds and infant seedlings since they can use only the food stored for them until their first true leaf appears soon after emergence. There is a choice of lean mediums: those with soil, those with no soil and no nutrients. The old standard mixture is loam, peat moss that has been thoroughly soaked and drained, and coarse concrete sand - the 3 mixed in equal amounts. This mixture has enough sponge to retard drying, and the air and water circulation is fairly good - but I often add a little 3/4" minus (which is crushed rock measuring from 3/4" down to particle size) for more openness. Packaged soil substitutes are sterile and usually nutrient free. There is bagged vermiculite, which is mineral in origin (it is expanded mica) and perlite, a mineral less volcanic rock exploded like popcorn under high temperatures. Vermiculite’s plate like structure is similar to that of clay, and it holds large amounts of water, which perlite with its simple smooth surface cannot do. Since I have not used soil substitutes I consulted a nurseryman who has. He relieves the problems of each by mixing vermiculite and perlite in equal amounts. He sows his seeds on the dry mixture, barely covers them with vermiculite, and then places the flats in a soak tray. He waters from the bottom to avoid washing the mix around, which can bunch or bury the seed. He believes that water coming up through a dry mix anchors the seed better than sowing it on a wet mix. After a thorough soak he transfers the flats to parallel 2 x 4 “tracks” which allow a great deal of air space beneath. I have since learned that an expert amateur I know, working independently, has devised the same medium and soaking procedure and will use no other. I’m anxious to try it next spring. Home gardeners have thought out mixes of their own. Some use equal parts of soil and perlite, and some mix soil with vermiculite. The vermiculite mix would improve with some coarse sand, or 3/4" minus, or perlite. Sphagnum moss used to be a popular seeding medium, but is seldom used any more. Because of its water holding nature, coarse sand or sharp rock mixed with it should be an improvement. I have used straight Canadian sphagnum after pre-soaking and draining, packing it firmly to the top of a shallow flat with very wide drainage cracks. (I’m told that sphagnum planting is especially effective for primula in the Soldanelloides Section.) It was a good germinating medium, but like all unfertilized soil substitutes, the seedlings had to be transferred to a fertile mix as soon as the first true leaf appeared. Incidentally, before I’m finished, a word about soil sterilization. Since I was not equipped for it I never did it. And recently I’ve learned that certain micro organisms in the soil multiply their numbers more than 5 times within a few days after soil sterilization. So what is the point of it if air and water circulation is poor enough to attract the disease producing organisms. Sterilization alone does not guarantee immunity.”
RLC: Thanks Florence. That was a good summary.

Sowing the Seed

And now we come to the heart of the matter - sowing the seed. Suppose we stick with our Europe-America division. It seems to work out well. Europe?

Kennedy: “I use 4” deep boxes, about 18" x 14" for large seed sowings, or round plastic pots (thoroughly cleaned 3 1/2" to 5" pots, depending on seed quantity) for smaller sowings. I fill to within an inch of the top with a good growing on medium and press it down lightly with the fingers. I top this with about ¾” of my seed mix and tamp that too. Next, I water the compost, not too much - it should be just moist and no more - and spray the surface with a copper compound, using a fine spray. Seed is sown thinly and evenly, and always left uncovered. In fact primula seed should never be covered with any depth of soil, since many species definitely need light to germinate. There are no species known to prefer dark for germination, so on no account should a layer of opaque paper be placed over the pots. Next, I immerse the pot till the surface is wet. When you lift the pot from the water the seed are drawn tight against the soil, “set” I call it. Often I spray the surface again with the copper compound and put the pot in a clear plastic bag, securing it with a plastic-covered wire. This makes additional watering unnecessary until after the seed germinate. It prevents the compost from drying out - a common cause of failure.

Holt: Yes, primula seed is very sensitive to drying out during germination. If there is insufficient moisture during this critical period, germination can be very poor or fail completely. One way to reduce this danger is to put a 1/4" layer of wetted milled sphagnum moss on top of the seed compost before sowing, and sow the seed directly on this. (Incidentally Jack Drake says never water seeds from above, but always by immersion from below.) After I plant my seed (always in flats) I take an empty, same-size seed tray, and upturn it over the seeds as a cover; this in turn has a brick placed on it to prevent dislodging. When the first seeds sprout we water again with Benlate, apply a very thin coating of the seed compost over the seeds, and replace the covering tray until the seedlings come up through the compost. Then of course the cover comes off and is replaced by a fine netting, polyethelene, or glass cloche for protection. I have read of other ways to do this, Richard, and I’d like to review one of them briefly now. It’s based on the theory that most primula seeds germinate best at temperatures below 25 degrees C. (75 degrees F). At temperatures above 25 degrees C. almost all primula species need light to germinate. So, although it may not be optimum for all species, a temperature fluctuating between 10 and 20 degrees C. (50 and 68 degrees F) will give good germination of almost all primulas and should be the norm to aim at. Fortunately these conditions are easy to achieve in shaded frame or cool greenhouse, April through September, or even into October. Although the seed do not need light, it is best to allow light access just in case. Another temperature requirement, especially for old seed, is for stratification, a period of cold to break dormancy. The optimum time for this is around 4 weeks, much longer and the awakened seed may go back into dormancy again. 4 weeks at 5 degrees C (41 degrees F) in the presence of moisture is about right. The best way to achieve this is to sow the seed on a moist compost, wrap the pot in a polythene bag and put it in a fridge. Then remove into a well-lighted, warm room and keep moist. Germination should follow shortly.”

RLC: Great. That gives us something to work with. All right now Americans, do you do it any differently?

Anita: “I do my seed in the greenhouse to keep away varmints, and where I can watch them every day. I look at the seed trays every morning using a small hand glass. If any mold appears I mix 1 teaspoon of Benlate in a quart of water and spray everything. I also keep a fan running to create a tiny windstorm in the moist air. Air washing over seedings is good therapy for possible fungal disasters.”

Herb: “I use 4 1/2” square plastic pots instead of flats or boxes for psychological reasons. Because when transplanting I can do one pot in a limited time where I might hesitate to start on a whole flat. This way I can at least get some transplanted when they should be. I fill my pots to the top and then press down about 1/4" below the rim. I wet this, and plant, and then cover with about 1/8” of vermiculite for large seed (auricula and polyanthus) or just the merest dusting of vermiculite for fine (vialli, reidii, etc). That’s to keep the cover from lying directly on the seed. Because I cover all pots with a piece of cotton cloth (old sheets) cut to fit, then put a few grains of coarse chicken grit on the cloth to hold it in place. I water lightly with a fog nozzle, and set my pots outside on benches in full sun, wind, snow and rain. The cloth cover serves several purposes. It helps keep the surface moist, it keeps the birds from eating the seed, it keeps heavy rain from washing the seed out, and it makes it easy to water my near 1000 pots in a hurry with the hose when it doesn’t rain. I take the cloth off when the seed starts germinating. Incidentally, Richard, I have brought along two or three methods for seeding which were published in earlier issues of the Bulletin. I thought they might be of interest here. Would you like to hear about them?

RLC: Of course, Herb. What have you brought?

Herb Dickson: Here’s one by Maude Hannon, which appeared way back in 1968. She writes, “We have tried many methods but prefer to plant in clay pots and sink them into the soil outside before the winter freeze. We cover these with old burlap sacks so that rain and watering will not disturb the seed, and so that there is adequate ventilation. When the weather warms the little seeds will begin germination. We uncover them and place a pane of glass over, tilted a little for circulation. In our seeding mix we use Blue Whale, up to ½ if procurable, along with regular peat, sand, loam, etc. We believe that Blue Whale, the 100% organic soil builder and conditioner, with its antifungal action, has helped us maintain our record of never having damp-off or disease in the seed pans.” Here’s another - from J. E. Mason, dated 1968. “On the 12th of September I sifted some rotted alder wood (any rotted wood would probably do), placing the material 1/2” deep on a brick which I had previously set in a pan of water. The water was 1/2" deep with the brick in it. I left the whole assembly for several days till I was sure the proper moisture was being maintained, and then scattered polyanthus seed on the wood screenings. I then placed some of the dry screenings in a pepper shaker and sifted it over the seed, barely covering them. The whole thing was then left in a temperature of 60 degrees F. Three days after planting the seed began to germinate, and in 6 days I had the best germination I ever experienced. By October 24 the whole pan was ready to transplant.” And here’s the prize - a unique method developed by Marge Edgren and used by many of her friends. “If you have no greenhouse, why not try a sandwich bag? I have raised a surprising number of vigorous rock plants, including some difficult primula, without benefit of leaf mold, loam, sun, or compost. Here’s how I do it. When seeds arrive I prepare 2 sandwich bags for each packet, each containing half an ordinary paper towel folded into a small pad and well moistened with water. Half the seed is sprinkled on top of the pad in each bag. Then the bag tops are folded down, labeled and stapled shut. Both are left to await germination, one on a shelf at room temperature (65 to 70 degrees F), the other in an ordinary refrigerator (35 to 40 degrees F). No attempt is made to control light during this time. Seed in the warm bags generally germinates first - some in a few days, others at intervals from 2 to 6 weeks. And of course, some take months. As soon as germination occurs in any warm bag, the corresponding package in the refrigerator is removed to room temperature, and, in nearly all cases, germination follows in due course. The refrigerated bags generally do not begin to germinate for several weeks or months, but occasionally one sprouts after only a few days in the cold. After 3 months in the cold I generally take all bags out into the warm room for a week or two. Many will germinate during this trial period, but those which do not are returned to the cold. Most seeds in a bag germinate all at once, but not always. Sometimes they keep coming for several weeks or months and I try to be patient about that. If seeds under cold treatment germinate first, naturally, the warm bags are refrigerated immediately, even if they look rotted and moldy. A surprising number will come through. The length of time bags are kept around awaiting germination depends somewhat on the rarity and desirability of the seed. I have kept some for a year or two. There are both advantages and disadvantages to the method: Advantages: 1. Very little time and space are wasted on seeds that do not germinate. 2. Seeds are protected from natural disasters between planting and germination. 3. Treatment of successfully germinated seed can be repeated exactly in subsequent years. 4. Rates of germination can be determined almost exactly. 5. Seeds requiring cold treatment can be started at any time. 6. No pit house, frame or other special construction is necessary. Disadvantages: 1. In planting seed must be handled twice. 2. lack of soil factors, temperature fluctuations or other unknown natural condition may prevent some perfectly good seed from germinating. 3. There is a distressing amount of mold and bacterial growth on the toweling and seeds; disagreeable, but in most cases it does not interfere with the germination and growth of seeds. No measures need be taken to control it.”

RLC: Fascinating! Can anybody top that?

Rosetta: “Richard, I can try. Failure of seed to germinate is often due to drying out after the seed has taken in water and is no longer truly dormant, but before any sign of life can be seen. A seed starter made from a 2 liter plastic bottle can eliminate this problem. Once the medium is moistened and planted, one never has to water again. The water condenses on the sides and circulates back into the soil, sustaining the seedlings until they are ready for pricking out. The bottle cuts easily with scissors. Punch a hole in the side with a knife to insert the scissors and then cut the bottle carefully in two, leaving about 6” for the bottom. Next, cut the top back so that the lower edge fits inside the bottom part. This is important, so that water as it condenses will run back down in the medium. Do not put drain holes anywhere. And keep the cap on, but not tightened. This allows air in but keeps algae and fungi spores out. The whole thing makes a mini-greenhouse that can accommodate up to 50 seeds. Use a sterile medium and mix with water till all the soil is moist. Sprinkle the seed on top, then add just a little perlite to anchor the primary roots. Put the parts together, place in good light but out of direct sun, and forget it. Or, you can even freeze and thaw the seed, right in the container. Things can go wrong, for instance, if direct sun reaches the container it will promptly cook, not dry but cook, the seedlings. If you use any liquid or other fertilizer to moisten the soil the seedlings will come up quickly and just as promptly die. A little common sense will help your plants bubble with efflorescense. I now use another method for some of my best seed. I use a 6 part cavity tray, like you get from the greenhouse with 6 little plants in. One seed goes in each compartment. I always cover with a very little perlite, which lets in light but keeps a humid layer near the seed, and later anchors the primary roots into the planting mix. Perlite is so light that seedlings have no problem pushing through it. This method eliminates the pricking out of small plants. They grow on in the cavity until time for potting.”

RLC: I guess we’ve heard it all Florence, do you have anything to add, or would you care to sum up?

Florence: “No Richard. My methods have been pretty well covered, and we have all been presented with some things to think about.”

Fungus And Mold

Florence: “On second thought, I will add something about air. When we put seed into the soil we know that it needs moisture, but often overlook its need for oxygen. When the rains continue to saturate the soil seeds die for lack of oxygen, which wet soil excludes. When we sow or cover too deeply, the shoots run out of food and oxygen before they can emerge. I do not cover primula seed, for nowhere are germinating seeds and seedlings more dependent upon a brisk circulation of air and water than those grown in flats or pots under controlled conditions. Without it, damping-off fungi can wipe out an entire planting in a few hours. In the nursery I grew 200,000 seedlings a year. They were grown in roofed but otherwise open sheds, surrounded by young trees and thickets. So I had to learn to propagate in an air-retarded pocket. What I learned held all the simplicity of a miracle. After losing two benches of germinating seed to bread mold and damp-off one spring, I began sowing them as close to the bench top as possible for the greatest air drift round the seed, and the necks of the newly germinated seedlings. The lath frames I hung up in the early afternoon I took down in the evening so that the night breezes and the cool morning sun brushed across the benches for the longest possible time. And I learned to use little more than an inch of seeding mixture over a deep bench full of 3/4” minus gravel for air play around the roots, and a speed drip-away of water. My next lesson came with the near loss of a summer crop of transplanted seedlings which had begun to rot. I found that the drainage cracks in the flats had swollen shut with many waterings. With brace and bit I bored here and there right through soil and bottoms of more than a thousand flats. Then I had miniature railroad tracks of 2 x 4s laid, and elevated the flats across the rails for quick drip-away and air circulation. Then I cultivated the young transplants with a carving fork as deep as it would go and saved the crop with oxygen. What I did not know then was that I had also enlisted the help of the antibiotic producers. With air and water flowing freely I had created an environment attractive to the benevolent disease-fighting micro-organisms. For those not familiar with damp-off or wilt and how it works, there are 30 varieties of malign fungi capable of causing the disease. The most common one strikes seedlings near or at soil surface for as long as their necks are tender. When seed is sown too thickly, and the tiny seedlings are crowded together, drops of moisture collect in the forest of necks. Too much shade, poor air and water circulation - either or both - add greatly to the already unhealthy crowded condition. When damp-off hits the tender seedlings they collapse as though scalded. A number of fungicides have long been offered for the pre-treatment of seed to prevent damp-off. I tried one of them and killed 2 benches of seedlings. Perhaps I did not dilute it more than instructed. Or perhaps primrose seed is allergic to this particular fungicide. Whatever caused the disaster made me fear fungicides, soil drenches and fumigants from that day to this.”

Smith: “I sympathize with your feelings, Florence, but for one reason or another some of us feel we simply must take chemical measures against the possibility of fungal disasters. My seed often has bits of chaff in it which sneaks in fungal spores. A routine watering with Benlate, diluted according to the package directions, usually takes care of that.”

Rosetta: “Damp-off could be critical in my pop bottles, but I find that using a sterile mix just about eliminates the worry for me. If I’m in doubt however, Captan works very well. The Captan I mix with the seed, dry-roll it around to coat each. If fungal growth occurs after rooting I dust Captan or Lilly’s Rose Dust with fungicide in it over the surface.”

Kennedy: “Just to be safe I lace my initial immersion bath with Benomyl, and when the flats are in their final position they are sprayed with a 1 in 25 solution of Algofen by Mac Penney International to deter algae, liverwort and mosses. I spray the surrounding area, too. Other things are used over here. Chilton recommends a liquid copper fungicide, easy to make up in small quantities according to directions on the bottle (1/3 teaspoon in a half pint of water). Make up a fresh solution each time you use it. Others use Phalton or Fermate diluted with water, or Natriphene.

Kelly: “I agree with Florence. Primulas rarely give me a problem with damping off - they certainly rank among the most care-free in this regard. I’ve heard of drenching both seeds and medium in a fungicide, but have never taken such precautions.”

Dickson: “A rule I follow for good healthy plants is to keep seedlings growing fast.

Length of Time for Germination

RLC: How about length of time for germination?

Smith: “With such a huge genus and all the variable factors it’s hard to generalize Richard. Anything from 5 days to 5 weeks would be quite normal. I like the remarks Chilton made in this regard. They noted that with naturally occurring species, as many of our primulas are, there are built-in germination characteristics designed to ensure the survival of the species. Each separate seed therefore is programmed to germinate according to a particular set of circumstances. So naturally, you don’t expect every batch of seed to come up all at once, to do so in its natural environment is not in the plant’s best interest.

Kennedy: “Quite so. Germination is usually well advanced within 3 to 4 weeks, if you plant early.”

Rosetta: “Double seed can take a little longer - ten days to 6 weeks, or more and germination is almost always uneven. I transplant the first seedlings, disturbing the container as little as possible. Then I may water again with hot water (120 degrees F). There may be 3 successive germinations, with the actual doubles often being the slowest to start. Polyanthus is apt to germinate faster than acaulis. Actually I think germination depends on the temperature. In a cool greenhouse with only a heat cable it may take 6 weeks. That’s in late fall or winter. But if the temperature is 50 to 60 degrees outside it may take only 3 weeks. This is for the vernales group. Some species take longer.”

Kelley: “I agree about the temperature, Rosetta. We have a greenhouse in which we have rigged up a germinating chamber. This consists of a heat cable buried in the sand in one of the benches. Atop this is a window sash that can be propped up for ventilation, or for a lower temperature as germination occurs. We maintain a 60 to 75 degree F temperature. With bottom heat it’s surprising how quickly the seed trays will dry out - we check them daily for water. We lift out and water from the bottom as needed. With time, one begins to know when a tray needs watering just by its weight. I remove a tray from the chamber when it appears that germination is complete. I like to grow the seedlings a little cooler after germination - 60 to 65 degrees - to produce sturdy robust plants. There is no need to force them along.”

Florence: “You know Richard, germination is so remarkable. The reason for keeping the soil moist goes far beyond softening the seed coat. As soon as the embryo feels the touch of moisture, enzymes begin converting its packaged lunch into available substances. Insoluble starch becomes soluble sugar; insoluble proteins are broken down into soluble amino acids; insoluble minerals become soluble chemicals. With the energizing boost of these the embryo bursts through the softened walls. It twists this way and that as the infant root dives into the earth, obeying gravity. Then the newborn plant begins to breathe, to photosynthesize, on its own, after’ its own fashion. And with this breathing all parts and agents come together into a smoothly working whole. This is birth in the green world.”

How Long To Save A Flat Of Seed

RLC: How long, ladies and gentlemen, do you save a planted flat or pot of seeds before giving it up for lost?

Kennedy: “If germination fails to take place I would keep the containers intact for a year - if the seed was important. Moss, liverwort and algal growth are then problems, and ‘caking’ of the surface of soil-based compost. I treat some for these. The containers are kept moist, always. And this is worth noting: even when seedlings have emerged, it doesn’t seem to matter if they become frozen hard. Jack Drake says that no pan should be disposed of until it is at least two years old. The Chiltern people say the same thing, and note that they have had many seed coming through after this period.

Rosetta: “I keep my containers moist for 2 or 3 months. Then, as summer comes, I set them aside and let them dry out. Some varieties will then come up in the fall. Others are covered and left outside to freeze and thaw. This may do the trick and the seed will sprout the following spring if watered and cared for. I’m not one to save a long time.”

Kelley: “I will generally keep seed trays a whole growing season, if they don’t germinate as expected. Since I usually plant primula in January, this means keeping them around until fall. If there’s no action by that time they get unceremoniously heaved toward the compost pile. I’m not at this point growing anything so rare that I might want to fiddle around with alternate methods of germination if the first fails.”

From Sowing To Germination

RLC: Bernard, you haven’t said anything lately. How do you treat the sown pans of seed while awaiting germination?

Smith: “I leave the trays on the bench in the garage (which is also my potting bench.) I cover them with a plastic propagator cover until germination takes place. Then, I remove the cover. Speaking of Jack Drake, if I recall he places his pots in a cold frame or cold greenhouse (it’s late winter) and covers them with newspaper. (Doretta Klaber used to do it this way too). But plenty of air is allowed. The pots are examined every day for germination, and to see if further moisture is required. Pots are never, never allowed to dry out. The important thing is to keep the seeds shaded and out of the direct sunlight.”

Dickson: “I want to repeat what we just heard - never let your seed pans dry out. Keep them moist, but not soggy. I have my pots on a bench outside with light cloth covers on. These cloths come off when the seed start germinating, and I start to water from the bottom, I try to avoid sprinkling with water from above at this stage - maybe an occasional fine mist when I’m in a hurry. And I wait until they really need it. Then I give them a real bottom soaking. Keep the pots in the shade with good air circulation, protected from the drips, the beating rains and birds. These last are a major enemy of new seedlings. The seedlings need good light, but not strong sun. If they begin to spindle I give them more light and air.”

Rosetta: “I have a greenhouse and my pop bottle containers are plunged in a bench with heat cables. But in the house one could put the seed pans on shelves under fluorescent lights. A friend of mine in Pennsylvania completely encloses his seed pots in polyethelene bags and puts them on a north window sill. After the seedlings come up the bags are gradually opened as true leaves appear.

Transplanting

RLC: Now, before we finish let’s have just a word or two about transplanting and caring for the seedlings. Herb, when do you transplant?

Dickson: “I transplant soon after the first set of true leaves develop. I use flats with drainage in the bottom and filled with my standard growing medium -1 part garden soil, 1 part sand, 1 part peat, 1 part perlite or crushed tufa. I separate a few seedlings at a time for planting so they won’t dry out. I set the seedlings one inch each way, as deeply as I can without covering the base of the leaves. I keep my flats well-watered and in partial shade till they’re ready to plant out in their bedding plots. Ralph Balcom used to say (Winter, 1969) “Space seedlings 2” each way and dust the undersides of leaves every 2 months to keep aphids in check.”

RLC: Herb, you told us earlier about Marge Edgren and her method of seeding in sandwich bags. What’s the rest of that story?

Dickson: Wait a minute. . . let me find my notes. . . Ah - here we are. Marge says that the medium in which she plants her germinated seed is a soil-less one, composed of equal parts of sphagnum peat, perlite, sand, fine granite grit, and course granite grit. In the absence of feed stores, gravel or crushed rock can be substituted for the grit, but the quantities should be maintained. Only germinated seeds are planted. The rest are left in the bag to sprout later. Germinated seeds are lifted off the wet paper towel with tweezers; or, if the seedlings are numerous, and the plants strong growers, they are spread rapidly on top of the medium with the fingers. This is admittedly the most cumbersome part of the process. Planted pans are covered loosely with transparent plastic film (Saran Wrap is fine) and placed immediately under fluorescent lights in the basement. The tops of the pans are placed very close to the lights, usually within an inch, to promote fast compact growth of the seedlings. The pots are turned every day to shake down condensed moisture and to circulate air around the plants. Plastic covers are removed just as soon as the first true leaves appear. The lights used - 4-foot tubes - are always in pairs: one warm white and one daylight. Growlux are not necessary. Best of all, mature plants can be transplanted outside after only a few days of daylight acclimitization in a shady place outside.

RLC: Sensational! Florence, why don’t you summarize your practices for us. I’m sure no one here has raised more primula seedlings than you.

Florence: “The mechanics of transplanting from the lean seedling mix to a growing-on mix is basically the same as the preparation for seeding. Pots or flats should have wide cracks or holes, planted containers should be elevated for air and water circulation in a good air sweep; and I still put 3/4 minus in the bottom before adding about 2” of a good growing mix. This is tamped down, filled, and tamped again to just below the container edge. If you buy sacked potting soil or mix your own, don’t add concentrated fertilizers at this point, organic or inorganic. Some gardeners transplant before the first true leaves, and, though tedious, this is alright, even though the plant cannot take up nourishment or make sugar until that true leaf appears. However, when using a mix with no nutrients, transplanting in the cotyledon (the seed leaf) stage is necessary. Since the soil in my standard mix carries some nutrients it is easier for me to wait for the first true leaf or two and I understand that some gardeners wait an entire season to transplant, if the seedlings are not too crowded. Before lifting seedlings loosen the soil beneath them with a carving fork or ice pick to prevent root breakage, but loosen and lift only a few at a time to avoid drying. My dibble is my forefinger, and I make a hole deep enough to take the roots hanging straight down. The hand holding the seedling positions it with crown at soil surface while the dibbling finger and its thumb press roots and soil gently together. Space plants about 2" each way. As soon as each container is planted, water in or tray soak, place in the shade for a few days, then give them sun in the cooler hours. Elevate for drip-away and keep them moist but not wet. Occasionally cultivate lightly, after watering, with a kitchen fork. That’s all there is to it, Richard.”

RLC: Thank you Florence. Now, does anyone have a final word? We have about exhausted our topics for this season.

Smith: “Systems in the United Kingdom and the United States vary - we have seen that. But we can all agree I think that home raised seed or plants are better.”

Dickson: “I want to emphasize that the basic requirement is continual moisture.

Holt: “Herb is right about the moisture. It’s the key. Many people use too shallow trays or pans for sowing primula seed. These can dry out quickly at the vital stage. I prefer trays or pots not less than 3” deep. Then, gardeners like you and me, often buy various seeds ‘Just to try this or that this year.’ This is a mistake, and will lead to disappointment, unless one studies the requirements of the resultant plants and can provide the right environment. The vernales primroses are the exception - they should be in every garden.”

Kelley: “Two related points I can’t stress enough. First, the novice should not be discouraged. Though ‘more learned’ folk may seem to have some answers to some questions, it’s through years of experimentation, learning from others, and making many errors themselves that they find themselves with advice to offer. There is no one right way to go about all this. Just get going! Second, keep meticulous records of everything you do, not only regarding planting seeds, but also, how things are going in the garden - what plants do well, what plants don’t make it. No, you will not remember in 1986 what you did to attain success in 1985. Records will be your most valuable asset as you proceed from year to year, and will keep you from repeating errors.

Photo Credit: Mary Kordes