Gardening in clay? Be a radish
Here in the GTA, we live in a clay belt.
Evergreen Brick Works, now the popular shopping and family entertainment destination in the middle of Toronto on Bayview Ave., is the former Don Valley Brick Works quarry and brick site that began production in the early 1900s. Our region’s natural clay has a long history, and literally helped to build Toronto and surrounding area.
But when it comes to gardening, there are few things as frustrating as bricklike clay that lies beneath the surface of what we loosely refer to as topsoil.
Mark experienced this last year when he purchased a one-acre site in Markham — where he now lives and plays in the garden. His vision included a pollinator garden, new trees and an extensive vegetable/ food garden.
Not so fast. He soon learned about a lurking clay base. “No problem,” he boldly thought and acquired an unconscionable volume of 70 per cent compost/30 per cent sand mix. About 300 cubic yards of the stuff arrived over several months from Miller Compost — one of the companies that composts residential leaves at their facility in Aurora.
What could go wrong? Lots, it turns out.
As winter snow melted and spring rains fell, the water moved down through the compost/sand mixture, eventually hitting a horizontal clay wall. It sat, stalled, about 20to-30 centimetres deep.
Mark diligently planted the garden and waited for his young seeds and plants to take off. They got a good start, but as soon as they hit the moisture, they began to rot. Some fighters pushed a root down to the clay and then began to voice their complaints with yellowing leaves and a lack of growth.
After consulting with several professionals in the soil business, here’s what Mark learned:
Clay can be nutrient rich. The problem is that the nutrients are locked up in the tiny soil particles that make up clay that binds them together.
Oxygen. All plants need oxygen at their root zone to breathe and thrive. Clay does not contain oxygen, as it is too dense. To help solve this problem, Mark had holes drilled in his garden last fall. A posthole digger was hired and dug down one metre deep, with holes 60 cm. apart, pulling up the clay base and mixing it with the compost/sand.
Magnesium. Chris Meier, business development manager and soil specialist with AL Canada, reminded Mark that magnesium, which his new garden lacked, “is part of the chlorophyll molecular, so all plants require adequate amounts of it.”
Chlorophyll is a main ingredient in the process of photosynthesis, the great miracle worker of plant growth. Without it, a plant can’t grow.
Come spring, Mark will add CalMag, a concentrated form of magnesium, to his existing soil to help make up the deficiency: four lbs. per 1,000 sq. ft.
This past November, fallen leaves were dragged onto the surface of Mark’s veggie garden. As those leaves rot, they will encourage microbial activity and habitat for beneficial insects.
In mid-August this coming year, he will sow tillage radish — its aggressive root can extend over a half a metre deep, which will help open the clay and release nutrients. The tillage radish will remain in the ground come spring, 2023 where the roots will rot, providing natural nitrogen and pockets of oxygen where none existed.
Complicated? Not really. A lot of work? Not if you like this kind of “work.”
Mark, a master gardener, is these days learning a lot about soil science — and he is thriving on it. A bit like a tillage radish.
MARK AND BEN CULLEN ARE EXPERT GARDENERS AND CONTRIBUTORS FOR THE STAR. FOLLOW MARK ON TWITTER: @MARKCULLEN4