If you live in a newly constructed home, chances are your soil is in need of help! Typical construction practices remove two to three feet of native topsoil, often leaving only hard clay remaining. The clay is then covered with a few inches of soil and sod. This practice wreaks havoc on the soil. The subsoil underneath is so compacted that it essentially acts like concrete and plants must struggle to survive.
Soils in natural conditions have many layers - each layer has different chemical and physical properties that have distinct roles in the soil's overall function. The top two layers are the most important for trees as they contain the nutrients, water, organic matter and air spaces that roots need to grow.
Signs of disturbed soil:
- Compacted and hard to dig in
- Little or no organic matter (the dark layer near the top of healthy soil)
- Hard, clay-like texture with few air pockets
- Hard surface that water runs off of, rather than soaking into
Soil improvements are most effective when performed before landscaping or laying sod. However, if you have already begun landscaping your yard, there are still actions you can take to mitigate soil damage.
If you have not started to landscape or lay sod yet, give your soil an overhaul by mixing in plenty of compost or other organic matter. This process needs to be done BEFORE tree and shrub planting since digging can seriously damage roots. Use a shovel or digging fork to mix the amendments into the top 10-12 inches of soil.
You will need to mix amendments over large planting areas, such as your whole lawn (before sod is laid) or in a large planting bed. It will not help trees and other plants to mix in amendments in small holes at the time of planting. Tree roots grow quickly and need to spread out into the surrounding soil. The small "pots" created by amending only an area large enough for the existing roots when the tree is planted will restrict root growth and negatively affect the health of the tree.
Please note: DO NOT disturb the soil around existing trees by digging up the soil or changing the grade. Even small changes in the amount of soil can cause severe root damage, and in some cases, the death of the tree.
Where tree roots already exist, soil amendments must be done gradually. Simply sprinkle a thin layer of compost or well-composted manure on top of the ground, making sure to keep it from touching or piling up against the truck, and applying it at least as far out as the branches reach. This organic matter will gradually work its way down into the soil below. Apply again when you notice that most of the compost has disappeared. Maintaining a layer of woodchip mulch in a doughnut shape around the base of the trees will also help.
If you have already started to landscape your yard, follow the steps below. These steps should be carried out regularly to maintain healthy soil balance.
- Much around trees and other plants. Mulch protects soil from the damaging elements of sun, wind, and rainfall it would otherwise be exposed to, if bare. It also helps conserve moisture in the soil and limits weed growth. Soil not covered with plants or grass should be covered with a two to four-inch layer of mulch (wood chips, leaves or other organic matter). Mulching with compost is especially beneficial because earthworms and other soil life move through the mulch and help carry these materials down into the soil. You can also place mulch around trees (always in a “doughnut” shape, leaving 6” of space between the mulch and the trunk) and other plants.
- Leave your leaves and grass clippings. Leaving the leaves that fall from your tree and the clippings from your lawn is a simple step to get organic matter and nutrients into your soil. Grass clippings are full of nitrogen and other nutrients and break down quickly to provide free fertilizer for your lawn. You don't need a special type of mower to leave clippings on the lawn; just keep the blades on your mower sharp. The City of Toronto no longer collects grass clippings as garbage or yard waste, so the best thing to do is leave them.
- Fertilize with compost, not chemicals. Chemical fertilizers do more harm than good to lawns in the long term – not to mention the harm they can do to our health. Instead of using chemical fertilizers, sprinkle a layer (about ½ inch) of compost over the entire surface of your lawn and garden in the spring and fall. You can use a spreader or top-dressing machine, or simply sprinkle by hand. On lawns, make the spring application at least three weeks before your first mowing. After a couple of years, you can reduce the application to one treatment of a ¼ inch layer applied in the fall. Free compost can be picked up from the City of Toronto’s Community Environment Days.
- Aerate your lawn. Removing small plugs of soil allows water and nutrients to penetrate more deeply in compacted soils, helping to speed up the process of soil restoration. Contact an organic lawn care company to enquire about this service. (Note that earthworms also aerate the soil – fertilizing with compost over chemicals will help encourage them to stay in your yard.)
- Water wisely. Sometimes, rainfall will provide all of the water your lawn requires. About an inch of water per week in summer is enough. If you do water, one deep watering per week in the early morning is best. More frequent, shallow watering will only encourage a small, shallow root system. Over-watering can cause roots to rot.
Signs of soil improvement:
- There is a layer of organic matter present; the top layer of soil is darker in colour
- Water soaks in rather than running off
- The texture gradually becomes less clay-like and there are more air pockets
- It's easier to dig in (this may take some time)
- There are more worms visible when you dig.
Note: if you suspect your soil has nutrient imbalances, it's best to have samples analyzed by a soil testing laboratory. Click here for a list of accredited soil testing facilities in Ontario.