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Roots vs. Soils: The Big Issue for Gardeners
Most gardeners don’t mind some hard work, but they don’t necessarily want to be digging the Suez Canal by hand or excavating the Rockies.
“Impossible” soils are those wonderful additions to every garden which just won’t do anything. They can be soggy, rocklike, or just barren and uncooperative. The problem for the gardener is that they have to be managed and turned into something useful.
Understanding Hard Soils
The first step in dealing with tough soils is to check them out in detail. The soil is the local history of that area, every single part of it. There are a few different types of hard soils:
- Highly impacted soils usually have a history of soil composition, including sand, involved. These soils are literally like rocks. The sand also affects the nature of the drainage, and if on a slope, can be cut to pieces by too much water.
- Barren soils may have been exposed to chemicals, herbicides, lacked adequate drainage, nutrients, or a combination of these factors.
- Old industrial land can have some truly strange chemical cocktails in it, including a lot of petrol, which is no help to plants, and may be toxic. (Do not plant food crops in this soil, unless you are certain it is safe to do so.)
- Old farmland can have similar properties to industrial but may have been rendered infertile by too many fertilizers and the crops themselves, which literally leach nutrients out of the ground.
- Clay is a mixed blessing. If it’s on a slope, it can be a real problem and should be checked for stability.
- Rocky soils are more trouble than they’re worth. Unless you want to start a quarry, any soil with a lot of embedded gravel and sand is probably an exposed old river bed or post-glacial deposits.
How to Dig Hard Soil
Highly impacted soils are more trouble than they’re worth for digging. If you can’t get your spade into the soil deeply, it’s likely to be hard labor, particularly if it’s flat ground.
There is a way to break up this soil manually, but it involves using a crowbar and if you want to experience arthritis without actually having arthritis, that’s how.
If the soil is too hard, the “no-dig” option is definitely the best. The good news is that raised beds and supports will sit securely in this soil, but you’ll need to hammer in the corners and supports for your beds.
Soil stability also needs to be covered and may require retaining walls, tree and grass planting, or cutting back the soil on slopes to reduce the risk of a mudslide.
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Barren soils may be improved by a combination of compost, worms, and a version of the “no-dig” methods, in which the soil is lightly turned, but not actually dug deeply.
There’s no point in digging this sort of soil because it provides a lot of soil volume, but is basically filler. The real work for plantings will be done by the imported soils. The idea is to break the surface and allow the new soil to “grow” downwards, as the live chemistry in the new soil breaks up the old soil.
Clay should either be left alone or stabilized with trees and bushes. Roses like clay, because it’s acidic, but other plants really don’t.
You can break up clay with lime, but it’s very hard work, particularly if there’s a lot of clay. Soil placed over base clay should be thick, fibrous, and have a layer of sand or gravel underneath. Treat the soil as bedrock, like the other “no-dig” scenarios.
Old farmland soils should be thoroughly broken up, like the barren soils, to a depth of about six inches, but no more. They’re used to getting dug up, but the lower levels aren’t. A lot of compost and patient application of nutrients with the right NPK mix, and in some cases nitrogen-rich crops like Lucerne will rehabilitate this soil.
Chemical Compromised Soil
Chemically compromised soil is tricky, at best.
Old industrial sites are often so old there are no accurate records of their use. You may want to send soil samples for testing before planting anything. These soils can be cosmetically fixed, and you can add a good layer of soil over it, but it’s advisable to cover it with sand or some other complete cover, to create a layer of separation between it and your plantings.
Leachates from these soils can include lead, heavy metals, mercury and other toxins.
Rocky soil, without exception, should be covered thickly with compost and soil mix. The good news about rocky soils is that their drainage is usually excellent. If you’re growing plants that don’t like getting their feet wet, these soils can be adapted like rockeries and will be fine as long as the plants have good footings and enough nutrients.
If you’re not sure, check out the local plants growing in the area. Trees and grasses in particular, if they’re natives, can rehabilitate poor soils by breaking them up with their roots and restarting the local soil chemistry. This is the cheap, all-purpose option for the impossible soils, and it’s much less hard work.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
James lambert on August 16, 2019:
How to break up clay soils
Hello, hello, from London, UK on September 24, 2010:
Good advice thank you.