Liza Drozdov – Halton Master Gardener
After decades of staring at my broken and ugly concrete driveway and imagining fragrance and blossoms in its space, I finally decided to break it up, take it away and create a new garden area. For the most part I want the garden to be given over to flowering perennials for pollinators. It’s the sunniest part of my garden–perhaps the only part that faces south and has full sun. It’s valuable real estate, in garden terms–far too precious to give over to a driveway! This driveway was made sometime in the 1940’s, and it was made up a layer of bricks over a 5-inch thick layer of poured concrete. It’s been eighty years since the earth under that concrete has been exposed to oxygen, light, or precipitation. I can’t tell you much about that soil, but there’s one thing I know for sure: it’s dead.
Creating a garden in dead soil is going to be an interesting proposition, mostly because you really can’t do a good job of it. Plants won’t survive, let alone thrive, apart from those most tolerant of low-nutrients and lack of organic matter. Good garden soil should be alive. It needs to breathe, and it needs air and water, none of which mine has had for many decades.
How do you know soil is dead?
I live and garden on sandy soil, which is low-nutrient in general, so I’m used to dealing with poor soil. But this is the worst I’ve seen. Any microorganisms that might have lived in it are long gone. There are no worms or insects, no humus, nor any organic matter. Sure, it’s easy digging (once I broke up and removed the concrete that had entombed the soil). And, I guess there are no viable weed seeds after this long–so that’s not a bad thing. But it’s lifeless.
It’s much like the soil many people are dealing with when trying to create gardens in new subdivisions. It’s very common for property developers to scrape off the top layer of soil and sell it off before breaking ground. Then, when the houses are completed, what’s left behind is subsoil–the least hospitable growing medium. People gardening in new houses are typically faced with subsoil, and wonder why their gardens struggle and fail. (It’s not your fault, btw.) Subsoil is typically light in colour, which indicates less organic matter is present, and that contributes to the low fertility and lack of moisture. Topsoil is the ‘living layer’ where plants grow. It’s closest to the surface, and it’s where the most bacteria and fungi live. It also contains organic matter, which helps retain moisture. This is the kind of soil you want in your garden.
What is ideal soil?
Healthy soil is not just an inert medium that holds plant roots and water. It’s a living thing, full of countless microorganisms, fungi and bacteria that interact with the plant, in a complex nutrient exchange that mutually supports both plant and life. There’s an ecosystem present in soil: plants and organisms live and die, they feed off one another, they decompose and over time that enriches the soil by creating organic matter. It’s full of organisms, like soil mites, millipedes, fungi and bacteria, algae, springtails and earthworms. And healthy soil is what you need to grow healthy plants.
Since my plan is to develop the new driveway area into a garden, I definitely have my work cut out for me. There is no way the plants I want to grow will flourish in that stuff. It’s not soil–it’s dirt. But the roses, clematis and other flowers I plan on planting are heavy feeders. They are hungry plants and if the soil isn’t brought back to life and enriched they’ll starve.
Why can’t I just use fertilizer?
Many people will tell you to just use fertilizer to compensate for lack of nutrients present in the soil, but that’s not a sustainable solution. The continued use of fertilizers (not to mention herbicides and pesticides) depletes the soil over time and there is evidence it can kill off bacteria and fungi and other essential nutrients. What’s most important is to improve the soil texture, its ability to retain moisture, and its organic content.
Healthy soil is a system, a web, and all parts need to be considered. Using fertilizers, even organic ones, isn’t sufficient to restore soil quality. The best analogy I’ve heard is comparing it to humans remaining healthy by eating a balanced diet, versus living on multi-vitamins. Save your money on fertilizers and feed your soil instead.
How can I restore my soil?
Soil is resilient and it can be brought back to life, which is good news. The first step in this process is to amend the soil to provide nutrition and enhance the ability of the soil to retain moisture. I add shredded leaves and manure or compost to my garden every year as mulch, but I don’t have enough leaves for this large a project. So I’m digging in a lot of ground pine mulch and several yards of well-rotted manure to do the job.
Any compost or animal manure is beneficial, especially if it’s supplemented with shredded leaves or similar material. (Cow, sheep or horse manure is better than chicken in terms of volume of organic matter, though chicken has a higher nutrient content.)
This simple step alone will help build the soil and allow plant roots better access to water. It will decrease soil compaction, improve aeration and begin to create an environment more attractive to earthworms and other soil organisms.
Since my soil is so poor, I’m adding an equal volume of amendments to soil, which may seem like a lot. But, since I’m starting at zero I think it’s about right. And, I’ll need to keep up an annual mulch to keep that soil quality high over the years.
I don’t know how long it will take for microorganisms, bacteria, fungi, insects and earthworms to return to the garden. But, by enriching the soil with organic matter and opening it up to oxygen, light and moisture, I’m sure it won’t be long before it returns to life.