Cool days are here, and it’s time to address the more arduous tasks that we avoided in warmer months: soil renovation. Now that we know full-scale tilling and turning over of soil disturbs the delicate microbial systems at work beneath our feet (no more double digging!), we can be more selective about where to make improvements. My strategy is to improve the drainage and oxygen content in the soil surrounding perennial plants, and anywhere I’m counting on plants to produce sustained bursts of bloom through the season.
Perennials starved for oxygen can’t make lots of flowers. Plants take up oxygen (and nitrogen in gaseous form) through their roots, and a healthy supply is essential for flower production. Dense or compacted soil has few pores, or air spaces, for water to drain away and to allow oxygen to penetrate the root zone.
How to do your own soil renovation
I dig in generous amounts of leaves around perennials when I divide or move them, and also the cones from a white spruce tree (Picea glauca, Zone 3) brought down from a neighbour’s cottage and planted in my garden six decades before I lived here—so it’s not a baby! The small cones that fall on the lawn are simply trodden in, and I collect a basket from under the tree to use as a soil amendment. Their bulky form holds oxygen in the soil, and they’re just the right size for roots to grow around in planting holes. Yes, a gardener’s eccentricity, but I wouldn’t be without them. You might find a white cedar in a city park, on a university campus or at your cottage, and now is a good time to look for cones under it. I also have a large Norway spruce (Picea abies, Zone 4), which produces bushels of wonderful needles I also use in planting holes.
Another soil amendment I rely on is rock in various sizes and forms. Using rock materials as amendments improves the porosity of clay-based soil. Of course, rocks come in many mineral compositions and sizes. The one rock material absolutely not to use in soil is limestone screenings, which are used as foundation for stone or brick walkways and patios. Limestone screenings are chalky-white crushed pieces of almost pure lime, and highly calciferous (alkaline)—plant roots shrivel up in contact with them. Fortunately, they are manufactured and not something you’d find lying about the garden, so you’ll easily avoid them.
I always have a bag or bucket of simple crushed stone grit, or quarter-inch gravel, or half-inch pea gravel that I mix into planting holes to improve the movement of water and oxygen around plant roots. If a perennial is doing poorly, but shows no signs of disease, I’ll lift it and renovate the hole with whatever rock material is on hand, then settle the plant back in. It’s often difficult to identify the mixed mineral components of these materials, but my general rule is never use rock that appears too white (that lime issue again). Dark or dull grey (sometimes splashed through with semi-translucent quartz, or sparkly with mica) is always a good sign as it indicates the presence of granite, an acidic igneous rock that helps balance the pH of our alkaline soils in southern Ontario.
Finding these materials isn’t always easy, and construction-supply yards and stone quarries often require a minimum purchase of several cubic yards. Sometimes they will admire your interest and allow you to fill your bucket for a small cost (or no cost at all). The easiest rock material to acquire is coarse builders’ sand, sold at home improvement stores. The particles in play sand or horticultural sand are too fine and small, and will make soil dense, quite the opposite of creating pore spaces. Roll sand between your hands to test the particle size—play or horticultural sand will be soft and smooth, and you won’t feel individual grains. But coarse builders’ sand has larger particles, and it will be sharp, with individual grains you can feel. No, I don’t have rocks in my head—they’re in my garden soil!
Defeating the columbine leaf miner
Cleaning up the garden gives me a chance to remember how much pleasure has come from individual plants—in this case, dwarf Biedermeier columbines (Aquilegia Biedermeier Group, Zone 4), sometimes known as the nosegay columbine because of its flower-packed stems, just ready to be cut for a small bouquet. Let me say they aren’t really so dwarf—described as 12 inches (30 cm) tall, but more like 18 inches (45 cm) in flower. Columbines are usually short-lived perennials, disappearing after a few seasons. But my Biedermeiers have hung on for five years, and produced a few seedlings with clear and attractive colours. I think it was Patrick Lima who wrote about their resistance to columbine leaf miner, a pest I have herds of here on the ranch! You’re probably familiar with the circuitous white tracks they weave through leaf tissues, eventually sapping the plant of energy and causing wilt. But the Biedermeiers are not to their taste and the miners leave them untouched. The strain has benefited from a bit of the hybridist’s art, and their flowers are outward facing and fully visible.
Still blooming: yellow fumitory
What would I do without yellow fumitory (Corydalis lutea, Zone 4)? It seems to have the genius of finding a perfect place for itself, filling vacant dusty corners and draping sprays of bright yellow flowers over rocks and between the bare ankles of shrubs—but never anyplace where I would want it removed. Does this plant read my mind? In mid-October yellow fumitory is as bright and full as it was in July. It spreads by seed, and acquiring just a few pots will insure you have it for all time. If it should pop up inappropriately, a gentle sigh of dissatisfaction will easily remove it.
Thanks for stopping by at Garden Making—hope to see you next week.