Living Soils

Primula’s Perfect Environment
by Mary Kordes

Are you planning to break new ground to make yet another garden, or to expand your existing one? Perhaps you need to redo your garden, lift and divide your plants, regroup for a better design, or add new plants. Most of your plant “actors” may have already given auditions, but have you thought about their stage? The very foundation of your garden, the stage that will support your entire show, is your soil. It will provide the home and food source for perhaps the lifetime of each and every plant in your cast. Every soil can use a boost to at least replenish the organic matter. The soil microorganisms, those “good little guys” who populate our soils, eat constantly as they turn that organic matter into humus and usable plant food.

HUMIFICATION
The word humus has become a catchall encompassing any organic material we add our soil but, unless these materials are partially digested to put them in an advanced stage of decomposition, they are correctly labeled organic matter. Through the process of humification, organic matter eventually decomposes to the very finest of particles and only then becomes humus. It is the wondrous world of microorganisms within our soil that breaks down organic matter during humification. There are millions of them in each spoonful of soil - from bacteria, yeasts, fungi and others, on to the tiniest one celled protozoa. As each organism family eats once-living organic matter in its varying stages of decomposition, it is linked to the next family in the chain of interdependent microorganisms. The completion of the life cycle of one family signals the beginning of another family’s uniquely specialized task. Humification finally, through consumption and digestion by these microorganisms and through chemical processes, reduces the organic matter to simple elements.

MINERAL NUTRIENTS
Acids produced through the carbon dioxide released by soil bacteria during the process of humification also play a key role in plant nutrition. These acids dissolve minerals in the inorganic components of soil, the mineral rock particles that make up all soils, to make these minerals available through the soil water. As the humus content in our soils is consumed and depleted, the numbers of microorganisms it can support decreases and the production of available plant food slows. Humus does eventually reach a point where it no longer contains reusable plant food. Therefore, the organic matter in our soil must continually be replenished to assure a healthy, active micro-organism community. Also, adding fresh organic materials to the soil stimulates soil bacteria and hastens the decomposition and nutrient release of humus already in the soil.

SOIL STRUCTURE
These soil organisms need humus for another reason, too, namely good soil structure. This means a soil that is loose and fluffy enough to allow free movement of air and with enough organic matter to retain moisture. Humus is the stuff that builds good soil structure and is the critical component for the soil organisms to recycle with maximum efficiency. Our soil friends also need warmth for stimulation. They are most active when the soil is warmed by the sun.

Loam soil consists of a balance of clay, sand and humus and is the ideal soil for most plants. Not many of us are lucky enough to be gardening in loam, but we can amend our soil to make loam. Organic matter serves to loosen and lighten heavy clay soils. You should also add quantities of a sharp sand/smaller gravel mixture to spread apart the fine clay particles, thus opening it for better drainage and aeration. Be careful not to work clay soils when they are wet as this will destroy the soil structure and lead to compaction.

Sandy soil, on the other hand, needs plenty of organic matter to absorb and hold any moisture that falls upon it. The addition of some clay soil to the sandy soil also greatly improves texture and nutrient exchange. I am lucky enough to have clay at hand to add to the thin, somewhat sandy, acid soil in some of my gardens. The finer clay particles serve to hold the soil together and also collect more moisture as each particle is coated with a thin film of cohesion water.

Black, crumbly compost and aged animal manures add wonderful fiber to your soil for texture and moisture retention, and they contain nutrients. Spent mushroom compost is another excellent source. Sphagnum peat moss is readily available at garden centers, and is one of the most-used soil conditioners. It is slower to break down than most fibers, so doesn’t add nutrients as readily as do other organic materials. Peat moss must always be dampened before mixing with your soil. I prefer to add hot water to a pail or plastic bag partially full of peat moss, then stir and knead it with my hands until it is damp enough to hold together in a loose ball without being soggy.

COMPOSTING
Organic matter in its rough, predigested state is the very best conditioner we can add to soil. There is no need to compost it first, though we do compost surplus plant residue. Work the materials into the soil or simply tuck them under your mulch so the “good little guys” can begin their work. The soil organisms will chomp on them with gusto to reduce them to minuscule particles. You won’t lose an iota of the nutrients those organic materials contain as can happen when composting. There will be no leaching to runoff or to the atmosphere, and all the goodness in the materials will go right back into the soil to feed your plants. Chopping the organic materials to small, but not compacted, particles affords more surfaces for the soil microorganisms to attack and speeds recycling to usable plant food. If you don’t have a shredder, chop your organic materials with your lawn mower. Rake the materials, including all the leaves you can collect in the fall, into wide rows and run over them with your lawn mower. Repeat the process until they are chopped to as fine a texture as can easily be handled.

Plant trimmings, grass clippings, weeds, leaves, sawdust, wood chips or bark, corn cobs, seed hulls, seaweed, and even human and animal hair combings are just some of the valuable sources of organic matter. But one word of caution: don’t use any plant residue that has been treated with an herbicide, as it may affect the plants you want to feed. I also frown upon grass clippings containing dandelion blossoms as their seeds continue to develop even after cutting, and I am sick of pulling healthy dandelion plants out of the gardens! By all means, don’t recycle quack grass. Those beautiful long, white roots, even when chopped, will grow and grow. Though all organic materials are rich, nutrient values do vary. The type of organic matter, and what nutrients and minerals it originally used to grow, will determine benefits received. So it’s back to the adage, “Variety is the spice of life.” Don’t waste a scrap of any plant residue. Shove it right back into the soil to begin that wondrous cycle once again.

NITROGEN SOURCES
Since nitrogen found in the protein of organic materials is the most important food of soil microorganisms, I like to add a dusting of an extra rich nitrogenous source along with the organic materials to stimulate those organisms and get them working. Aged manure (never add fresh manure as it is too “hot” and will burn plants), blood meal, and fish meal are high in protein. But don’t confuse protein in organic matter with the protein we derive from meat. No unprocessed meat product should ever be added to either a compost pile or your garden, as it will surely attract rodents and other scavengers. Earth worms, too, will swarm in to enjoy the organic feast in your garden. They drag those wonderful organic particles down deep into the soil, creating tunnels as they go. Those tunnels are the magic roads to soil aeration, as fresh air seeps through them to provide the soil organisms and plant roots with needed oxygen. The best time for us to feed our soils is when preparing a bed for planting, as the soil can be deeply and thoroughly worked without disturbing plant roots. Alternatively, add more organic matter to soils at any time, working it into the soil between plants, or just by adding mulch and letting the earth worms carry it down into the soil.

SPECIAL ADDITIVES
Even loamy soil needs further amending to keep different plant families happy. Most of our primulas, for example, need extra organic matter for moisture retention. Auriculas require an extra portion of coarse sand and gravel to mimic the soil of their mountain origin and facilitate faster drainage. Beyond improving soil texture, soils can be deficient in nutrients. It is a good idea to take soil samples in your garden, then either test them with a soil test kit from your garden center or, for more in-depth scrutiny; go to your local State University Cooperative Extension office (if you live in the U.S.A.). They will advise you on the proper method for taking the sample and, after they analyze it, will supply you with a rundown of what your soil needs. A small fee is charged for this service. The term pH refers to a soil’s acidity or alkalinity. pH 7 is considered neutral on the pH scale. Soil organisms are happiest at pH 7, when the most plant foods are suspended in the soil water. Numbers higher than 7 indicate an alkaline soil, while lower numbers become increasingly acidic. Some soil organisms will be less active in either an acidic or alkaline soil. Therefore, certain nutrients will be lacking under these conditions, but that soil will still provide a perfect environment for particular plants.

Most plants, including the majority of our primulas, prefer a slightly acid soil. The addition of peat moss or cottonseed meal, if necessary, helps supply that acidity. But most primulas of the section Auricula require a more alkaline soil and may need a little lime, bone meal or wood ashes added to most soils to supply the calcium they crave. A mulch of crushed oyster shells also sweetens the soil as they slowly decompose. None of the food we give our plants can be used by them until it has been reduced to its original chemical form and suspended in the cohesion water that surrounds soil particles. Amending our soils with organic materials is the best assurance that soil bacteria will thrive and the chemical exchanges take place to produce healthy soil and plants. When your soil amendments have been made, there should be no further need to disturb the soil until you have to lift and divide your primulas. In fact, it is far kinder to the microorganisms who live in the soil not to destroy their community structure by cultivating your soil. If necessary, aeration of soil can be accomplished by merely pushing a garden fork or small fork-like hand tool into the soil and gently wiggling it back and forth without actually lifting out the soil.

MULCH
I like the unifying appearance of a 2-3 inch chopped leaf mulch on all of my gardens. It becomes a rich brown color and does an excellent job of suppressing weeds. Grass clippings are also good; they age to a lighter shade of brown. I have found that mulch retains soil moisture, but I must still be careful to water the gardens thoroughly, especially in dry spells. The mulch will absorb the moisture like a sponge and, unless enough water is applied, the underlying soil can become bone dry. This is especially true when gardening under trees. The tree roots tend to grow into the rich garden soil in search of both nutrients and moisture and will sap the soil leaving little for plants. Careful attention to watering is also important to microbial activity. Dry soil slows the process of humification by soil organisms, resulting in few nutrients available to plants.

Now that your soil is rich in humus, your stage has been properly constructed. It’s time to call in your cast of plant actors and get on with the show!

Photo Credit: Sally Arant of her gardens in Anchorage