Making Hypertufa Troughs

By Robert Tonkin

When Pam asked if I would volunteer to do one of the Community Garden Saturday Series this past summer I was at a loss as to what to talk about. Auricula came to mind, but after a bit more thought I was assured most everyone, especially Ed, has had their fill of auricula lectures for a while. What to talk about, hmmm? Wandering around my lower 40 acres I noticed the two unfilled hypertufa troughs in the yard and realized there aren’t that many troughs in Juneau. I wondered why; as they are perfect little micro settings, ideally suited for our growing conditions. They drain well (the biggest plus!), you have complete control of the type of soil you want to put into them, they are relatively inexpensive to make, and are somewhat portable.

So I decided to build a new trough at the Saturday event and add another empty trough to the yard. I really do intend to fill these troughs with plants, really I do. It’s just that I want those “special” plants to make my troughs ‘unique’. Not just any plant
will do you know. Having built two new raised beds for my auricula and marginata collections, I am still at somewhat of a loss as to what to put into the new troughs. More on this later.

As the weekend approached I realized I needed to have my materials together. Of course I procrastinated until the last moment. Saturday morning of the event found me at Fred Meyer’s buying needed perlite at prices I just cringed at. That will teach me not to buy the three-foot cubic bags before they are all gone. I figured I would build a trough that was about two feet by one and half feet by about eighteen inches deep. This size is somewhat portable, meaning if you actually needed to move it once it was full of dirt, it could be done with two strong backs and a bit of planning. Other materials that filled out the list were Portland Cement, (pure cement, not aggregate), peat moss, the perlite I mentioned already, Styrofoam insulation (the pieces sold in two by eight foot by two inch sheets), lotsa duck tape, a bit of hardware cloth to cover the drain hole (this prevents large critters from crawling up into the drain holes and having your precious plants for a midnight snack), and some cement dye if you are the creative type. I chose red for this one.

On the morning of the event I loaded all the materials just listed, along with a wheelbarrow, buckets, trowels and shovels into
the back of the pickup and drove out to the Community Garden for a fun filled mud pie fest! The appointed time rolled around and I found myself talking with two people. Well, this was going to be short. However over the next fifteen minutes or so another dozen folks meandered into the area to watch. Ahhh, Juneau time. Once everyone was assembled it promptly started to rain. So, we backed the truck up under the shelter and started with the demonstration.

I had already cut and assembled the mold out of the Styrofoam the weekend before the event. Have a look at the picture to see what it looked like. It is just a matter of using a straight edge to measure and cut the pieces off with a hand saw and then using that trusty old roll of duct tape to wrap them together. In addition to the duck tape, I use sixteen-penny nails pushed up from underneath the bottom of the mold to help secure the sides to the bottom. These help a great deal once the mold is filled with the hypertufa mixture. As you can see, you actually build two molds on top of the same piece of bottom Styrofoam. The outer box is of course the outside wall of the trough and another box becomes the inside wall and the bottom of the trough. I set the inside wall aside for the present time as we needed to mix up some hypertufa for the bottom of the trough before we set the inside box in on top of the outer box.

There are a number of mixture recommendations for making hypertufa. Notice I don’t use the word “recipe”. I always associate that word with dinner, so I won’t be using it here! The “Standard Mixture for American Made Hypertufa” contains 2 parts Portland cement, 3 parts sieved peat moss, and 3 parts perlite. Enough water is added to this mixture in a wheelbarrow to get the mix “just moist” Careful here, it is easy to add to much water, a common mistake for the beginner. Don’t put in more cement than what is called for. It won’t add any strength to the trough. Sieve the peat to remove any sticks and other free goodies commonly found in a bag of peat. Perlite is used right out of the bag. Be careful not to breathe the perlite dust, it’s nasty stuff! If you think you want to add some reinforcing agents, give consideration to plastic or fiberglass fibers that are commercially available. I don’t think they are needed and believe they detract from the esthetic beauty of the trough, but each to his/her own. Now is the time to add the cement dye if you are so moved. It is important to mix very, very well. I was most fortunate to have Ed there providing the mixing effort. This afforded me an opportunity to run off at the mouth while Ed did the mixing, rather than the other way around. It was great!

Having the mix prepared, it was then carefully hand trawled into the walls of the mold where a broom handle, cut off at about two feet, was used as a tamping down tool to compact the hypertufa as tight as I could get it down inside the walls of the trough. When you look at this mold, remember you are building this trough upside down. The inside “box” fits into the outside box and is exactly two inches less in height than the outside box. Notice I used a Styro-foam fish box for the inside box. I built the outer box exactly two inches larger than the inside box. The inside box supports the inside bottom of the trough. I used precut two inch small block pieces of Styrofoam as spacers between the walls to ensure the walls were square and the same thickness all around. The next batch of hypertufa was mixed, thank you Ed; darn he’s handy. The remainder of the walls and the bottom of the trough were filled and compacted and the whole thing was completed. I used a three and half inch plastic pot for the drain hole. I simply tear it out afterwards, and am left with an adequate drain plug for the trough.

I let the trough “cure” for about forty-eight to seventy-two hours before taking the mold off. I am careful when performing this task, as the same mold can be used three or four times again without any major problems. Just keep that roll of duck tape handy and label the pieces, as it might be some time before you build the next mold, and if your memory is getting anything like mine, you will be very pleased with yourself you took the time to number and label the pieces. Be very careful about moving the trough at all at this time. Try not to move it at all if possible. It’s hard to do, as you need to slide the mold out from under it, but be very careful. This is where the cracks and damage usually occur. Leave the trough on the sawhorses or ground for another few days, covered from the rain, and then uncover it and let it cure for a good three to nine months before pressing into service. Some folks spread a bit of milk over the outside to encourage mold, (like it needs it around here) and to get rid of that “new” look. Each to his/her own. They will grow mold on their own over the years, along with everything else in the yard, and your house, and your knee joints and .....

Ok, next a bit on soils and finally what type of plants to put into your trough. Of course the first is going to be dictated by the latter. Hint: alpines do well in troughs. In fact, this is what most of us snooty gardeners use them for. Those precious little morsels of ego that only the completely addicted can appreciate. My first trough, pictured here somewhere, started out with the species arabis, draba, and few saxifrages and some sedums. I know this is a primula newsletter, but I begrudgingly admit there are other species nicely fitted to the trough. Think of the three S’s when you think of filling a trough the first time. Saxifraga, Sedum, and Sempervarium all do well in troughs and should be given serious consideration. Other alpines that might be worth a go are Androsace Lewisia, Campanula, miniature phlox, dianthus, and even miniature bulbs. Soils for these types of species need to be free flowing. A mixture of one third each sand, your favorite loam, and pea gravel or pumice make for a good mixture for these types of plants. Lean and free flowing is the way to go with these species.

In the primula world, you knew I was getting there right, consider P. auricula, angustifolia, aureata (for the very brave), capitata, cockburniana, cuneifolia, farinosa, frondosa, hirsuta, some julie’s, marginata, minima, pedemontana, any of the petiolaris (again if you are feeling lucky), pubescens, reidii, and rosea. These species may have different soil requirements than the list in the previous paragraph. A bit o common sense goes a long way here.

Give careful consideration to the location of the trough too. A trough out in the open may have a better chance of holding many of the primula that thrive on the moisture. The previously mentioned alpines, and some primula, would be happier under an overhang where rain did not beat them to a pulp most days. Build a couple and try both spots.

Experiment, have fun, kill some plants, plant new! Troughs make it a bit easier to create conditions that you have a bit more control over. The oldest one I have has a few nice pieces of Arabis bryoides, Androsace lactea, Sedum spathulifolium ‘Cape Blanco’ and, Sedum oregonense. Newcomers to the trough are P. rosea, hirsuta, and minima, all of which may or not make the winter. But hey, I got plenty of seed in the refrigerator. Good Luck!