All about Soil
To most people, soil looks pretty much like - well - soil. To the gardener it is his basic material, the stuff he has to work with, so it is worth his while knowing a little about it. Correct analysis of the soil is one of the key elements in the success - or otherwise - of growing certain kinds of plants. It is the type of soil in your garden (combined with one or two other factors, like where you live and how sheltered your garden is) which determine what you can grow and what you can't.
So, what is soil? Soil is basically made up of mineral particles with some organic matter mixed in it. (Unfortunately there is not much you can do about the mineral side.) The structure of soil covers quite a wide spectrum. At one end you have clay, and, at the other, sand. Dig up a bit and squeeze it between your fingers. If it feels sticky when you rub it between your fingers, and reminds you of the Plasticine you used to play with when you were young, then you have got clay. If it feels very gritty and you can see all the separate grains (you may even be able to hear the sound of the grains rubbing against one another) and it reminds you of the stuff that gets into your shoes when you walk along the beach, then you have got sand. Neither of these can be considered to be good soil, since sand, although it is well aerated, allows water to drain through it very quickly, while clay, which holds water, has its particles packed so tightly together that air cannot get into it. Fortunately most soils (but not all) lie in between these two extremes.
Nature has managed to cope perfectly well with poor soil conditions for millions of years by ensuring that only plants which can tolerate the conditions continue to propagate themselves. But we gardeners want to be better than nature and grow all sorts of different plants and not limit ourselves to those which like the basic soil. What we want is a loamy soil, a soil which feels light and friable to the touch and has a nice brown, earthy colour to it, the type of soil which will encourage earthworms to burrow and which is neither too dense nor too crumbly but capable of holding just the right amount of water to keep the plants healthy, a soil in which you can plant things with your fingers and not have to resort to using a trowel. If we have sand or clay, then we have to change the soil. One way is to dig it all out and replace it with a good top soil. However, although some things may be dirt cheap, dirt isn't one of them, so this method could turn out to be rather expensive as well as labour intensive. After all, to replace the soil down to a depth of twelve inches in a fairly small garden of 20ft. square you will have to dig out something like ten tons of soil (even more if it has been raining), and then move another ten tons to fill in the hole. Not my idea of fun.
No plant will survive unless the roots have access to a certain amount of oxygen, and heavy clay (people always seem to talk about heavy clay - I wonder what light clay looks and feels like) has such small particles that little air can penetrate it. Clay has to be made more porous. The best way to improve it is to dig in lots of grit and organic matter like horse manure or compost to hold the particles apart and let the air in. Adding lime can help, though this will make the soil more alkaline, which is certainly of little benefit if you want to grow rhododendrons and azaleas or heathers (especially the summer flowering ones). If the clay is heavily waterlogged as well some form of drainage may be required.
No plant will survive unless its roots have access to a certain amount of water with essential elements dissolved in it, and sand doesn't hold water. So, in periods of drought, plants will suffer and die. In this case, the answer is to dig in plenty of organic matter like horse manure or compost to bind the particles together and so retain the moisture.
No doubt you have heard that digging is good for the soil. To improve soil structure by adding different materials to it you have to dig it. It is also a simple way of aerating the soil. But each time the soil is turned over all the insects and bacteria living in the soil get a nasty shock. Instead of getting on with their jobs of chewing away and reducing all the organic matter in the soil into chemicals that the plants can use they have to start digging new tunnels and find new routes. (Just think what it would be like for you to move to a new house every year.) Once you have got the soil into a good, healthy condition, and you don't walk all over it (especially when it is wet), then there shouldn't be the need to dig and dig and dig. You can leave all that sort of thing to the worms. All you have to do is replace all the nutrients that the plants have taken up. You can use chemical fertilizers, like Growmore and rose fertilizer or tomato food, or more 'green' substances such as bone meal and dried blood. Or you can use manures like the stuff horses and chickens produce. These, if well rotted, can be used as a mulch - spread it over the ground and let the worms do the rest.
Happy Gardening.
Garden Gossip written by Bill Hutchings
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page last updated 2 NOVEMBER 1997