Soil differs from one area to another in the same way as water. One soil is rich in lime while another might be sandy. In some places, the stony origins of soil are still obvious, with lots of pebbles surfacing when you dig even a little below the surface.
The earth we dig into consists of three main layers. For gardeners, the top layer, extending to about 70 centimetres (2ft) below the surface and called topsoil, is especially important. This is where most of our garden plants live, although their roots spread into a looser, more granulated layer below. Called the subsoil, this is about as deep as the topsoil, but stonier. Finally comes the lower layer, which taps into the ground water. From this, moisture rises. To make soil fertile, water is absolutely vital and in well-drained soil, moisture passes up and down constantly through the three layers of earth.
Good soil is easy to recognise. It looks like the inside of a loaf of rough wholemeal bread – crumbly and evenly textured, with no big lumps or stones, and neither too wet nor too dry. Few of us are lucky enough to have soil so perfect and it can be both frustrating and fascinating to see what a seemingly ordinary suburban garden can throw up with a bit of digging. Broken china, hair combs, rotting wood, bricks, the metal remains of a paintbrush, plastic bags, and bits of bicycle and pram, are nothing unusual.
Most soil can be redeemed and turned into a good growing medium, though if your house is on a new housing estate and your garden covered in weeds and splattered with remnants of the builder’s labour, it may be worth saving yourself months of back-breaking work with no guarantee of any improvement by buying in new topsoil.
For the rest of us, the task is simple enough. When you start out, dig up as much as you can of your flowerbeds, using a spade and a fork. The best times are late autumn to kill off the remains of the season’s weeds and leave the garden looking tidy for the winter, and then sometime in March when the temperature starts rising and the ground is not frozen solid. Avoid digging at any time when the soil is very wet. Digging breaks up impacted clods of earth and refreshes the surface, which is probably covered with half-dead weeds and old grass, along with blown-in crisp bags and sweet wrappers. It also brings stones to the surface that can be collected for other uses, such as a soak pit in wetter parts of the garden. Clean up the soil as you go and take a couple of days if necessary: digging can be heavy work.
If the flowerbeds need serious resuscitation, there is the technique known as double digging, which will literally turn your garden upside down. You dig a trench about as deep as two spade lengths, putting the dug earth to one side and loosening the bottom of the trench with a fork. If you reach the orange subsoil, leave it alone. Next dig a new trench beside the first and turn the soil into the first, incorporating some compost, leaf-mould or manure as you go. And so on. When you come to the final trench, use the soil from the first trench to fill it up. This is heavy work, but once done, your bed will be easy to manage and will not need the same treatment for at least another five seasons, if ever. The bed will also be slightly raised, so you may like to contain it with bricks or a length of wood.
All soils have a certain amount of nutrients, vital for healthy plants. But these nutrients do not last forever and must be replaced, as nothing will grow otherwise. In the past, this was one reason why farmers would leave an overworked field lie fallow for a couple of years.
So how do we do enrich our soil and keep it healthy? First, it is useful to know what kind of soil you have, and for this purpose, we need a little bit of chemistry.
The term pH is a measure of acidity and alkalinity, with pH 7.0 the mid-point; pure water measures 7. A reading of 4.5 to 5.5 means the soil is very acid and ideal for rhododendrons, azaleas, camellias and most heathers. In a slightly acid soil, reading 5.5 to 6.5, most fruit trees and bushes will flourish, along with roses and lawn grass. Manure, chemical fertilizers and acid rain tend to make a soil acid; if this happens digging in some lime will cure the problem. Lime can be added to compost, but not to manure, as this will cause a release of ammonia gas and nitrogen will be lost from the soil. Neutral soil, reading 6.5 to 7.3, is the ideal and almost anything will grow in it. Alkaline soil, rich in lime, is yellow-ish and reads from 7.3 to 8.0. Carnations, wallflowers and cabbages prefer it. Too much lime is not a good thing as it causes soil to break up quickly.
Initially at least, you may not need to go to the bother of fiddling around with soil samples and test-tubes. A simple examination of your garden will give you plenty of clues. For a start, identify the weeds that flourish in your lawn and flowerbeds. If you get lots of daisies and plantain in the lawn, and maybe even thistles and buttercups, then your soil is acidic, or low in lime. Clover, by contrast, prefers an alkaline soil. If nettles are flourishing, count yourself lucky: the soil is particularly fertile. If there are any hydrangeas in the garden or nearby, observe their colour in summer. The blooms will turn pink with lime soil, blue with acid or purple in neutral soil.
Picking up a handful of earth can also tell a tale. If it looks and feels gritty and cannot be rolled into a ball, it is sandy and will need lots of sticky compost (cow or pig manure) to turn it into a suitable base for growing. It will also need lots of watering. On a positive note, it is easy to dig.
On the opposite end of the scale is a heavy soil. This one makes a sausage-shape when rolled in the hand; if you rub it between the fingers, it turns shiny because it is rich in clay. Think of the ideal soil for mud pies and you’ve got it. Water moves very slowly through this type of soil, so it can get waterlogged in winter and dried out in summer. It may need some kind of artificial drainage, or at the very least double digging in the autumn. This is heavy work; I would consider getting in a professional gardener and possibly a mechanical digger if you have this problem.
Fortunately, most of us have soil that falls somewhere between these two extremes. Your average soil is a bit like a light plum pudding – rich, but not too rich, and easy enough to handle. Rubbed in the hand, its breaks up into medium-sized “crumbs”. A good layer of rich compost in the autumn will keep it the way it is.
Don’t worry about your soil type too much. Most plants will grow in anything reasonable, dressed up with some good manure. The only ones I would avoid are the lime haters that refuse to grow in an alkaline soil. Remember, the secret of good gardening is finding the plants that suit your particular conditions. With luck, this will be a rewarding search.
In the typically overused garden, the humus content of your soil can do with a little help and there are many soil improvers for sale. In front of me, I have a 5kg bag of multi-purpose compost, which the providers boast is chemical-free and enriched with seaweed. It can be used for seed, potting and planting out. Along with the seaweed, it contains fully composted cattle manure, sphagnum, peat and sand. In any garden centre, you will find John Innes composts. Innes (1829-1904) left money in his will to found a school for training gardeners. His trustees founded a research institute instead and here, developed the John Innes soil-based seed and potting composts that exist to this day. The higher the number, the richer they are in fertilizer. So No. 1 is used for seedlings, No. 2 for potting on and No. 3 for plants like tomatoes and chrysanthemums. After using, throw into the compost heap.
Farmyard manure, widely available directly from farms in large quantities or in more manageable plastic packs from garden centres, is one of the best sources of nourishment for the soil. Chicken manure and mushroom compost are two varieties worth watching out for. Manure must be “well-rotted” before use. This is because manure generates a lot of heat when breaking down and if applied in this state, will damage a plant’s roots.
Peat moss, organic, weed-free and easy to handle, is also widely available, but comes from a valuable and dwindling natural resource. When the bogs go, a precious eco-system, supporting numerous wild plants insects and animals will be lost forever. The good news is that sphagnum moss, a renewable resource, may work as an alternative, while experiments are also being carried out on shredded coconut shells. So think before you buy your next sack of peat moss.
An alternative to peat moss is leaf mould, the brown, flaky material found beneath this year’s fall of leaves; in other words, the previous season’s leaves. To make your own, simply stack the rotting leaves in a wire-netting enclosure or put them in a black bin-bag, making a few holes in the sides of this and adding a special accelerator that is available in all garden centres. The best leaf mould comes from oak or beech. Leave out pine needles, plane, sycamore, holly or other leathery evergreens, as they will take too long to rot. Leafmould is ideal for woodland plants, like trilliums and snowdrops. It can also be used in potting mixture for alpines (one third leafmould to one third compost and one third grit). It can be crumbled up when rubbed between the hands or put through a coarse garden sieve. As a mulch, use it as it is.
Another essential for the gardener is bonemeal, a slow-acting fertilizer that is excellent for putting in the bottom of the planting hole in autumn and spring. It is particularly useful for bulbs, which are not generally partial to rich farmyard manure. Then there is sand and grit, essential for helping drainage. Horticultural sand only should be used. Grit consists of small chippings of stone and is invaluable for working into heavy soil. It is also used when making up composts for alpines and bulbs and when making a raised bed.
Mulching is used around shrubs, trees and herbaceous borders. It keeps the soil moist and cool during hot summer days so promoting growth, and, by starving them, helps keep weeds in check over the summer. With the help of hard-working worms and other insects, the goodness in the mulch is gradually dragged through the soil. Compost is not the only material used for mulching. Shredded bark, leaf mould and small pebbles or grit can be used. Some people use grass cuttings, but as these usually contain dormant seeds, it is not really a good idea unless you want grass to grow around your plants. On an overgrown bed, trample down the vegetation and then spread old cloth made from natural fibres, such as cotton sheets, curtains or even t-shirts, over the area. Cardboard boxes can also be used. Cover these with leaf mould or compost and allow to rot down. Plastic mulches in the form of black sheets can also be used, and are especially useful under a gravel drive way or path. Perforated sheets are available that let in air and water. But unlike organic cover-ups, plastic of any kind will do the soil no good in the long term.
The best time of the year for mulching is May. First prepare the soil by cleaning it up, removing dead leaves, weeds and other rubbish and giving everything a good watering if the warm weather has already set in. Sprinkle in a bit of fertilizer as well. Now spread a thin layer of your mulch under the branches and leaves, leaving the space directly around the stems clear. In the autumn, fork whatever remains of the mixture into the topsoil. Repeat the process the following spring. All mulches are attractive to snails and slugs, so be vigilant.
Making your own compost is not at all hard; any heap of vegetation will eventually rot down. But ideally, you need a confined space, such as a bin, to allow the refuse to generate heat and encourage bacteria. Air is also needed, as is water, though not too much – a waterlogged compost heap just won’t work. So find a good spot in the garden, preferably dry and shaded. That dull corner that grows nothing but moss could be ideal. You can buy a compost container or tumbler; these are probably best for the average city garden and work well. Still, making your own with some bricks and bits of timber is not too hard and ensures that it fits exactly into your space. To do this, build a small brick or wooden bin, with four sides and a rainproof lid. Find a piece of old carpet to cover the compost. Ideally, one of the side panels should be in two sections so that the top half can be lifted off to make the compost more accessible. Even better, make two wooden containers and as the compost heap matures, turn it into the
second container. This will leave the rotted compost on top and readily accessible. Also available in your local garden centre is a type of plastic fencing that can be made into a round compost bin for garden cuttings. So there are lots of options.
Into your bin, throw your garden and kitchen waste: fruit and vegetable leftovers, tea-bags, eggshells, grass cuttings, hedge clippings, shredded cardboard and paper, hair and wool. Seaweed, if you can get it, helps make excellent compost. To make the best use of your grass cuttings, cover a layer of grass with cardboard and repeat as necessary. Even clothes made of natural fibres can be added to the heap, though it is best to cut them up first. Do not add meat, fish, bread, or indeed, anything cooked or processed. These stink while rotting and attract rats. Deep-rooted perennial weeds are not a good idea for the compost heap while fresh, but once dried out, can be used. Otherwise, they are best burned.
It is important to get the mixture right – a layer of grass should be followed by a layer of kitchen refuse and a layer of manure or even garden soil to help speed up decay. Go easy on the grass cuttings, as they become slimy. Remember to keep the mixture covered. If the compost gets too wet, add straw, sawdust or even hedge clippings. You do not have to add to the compost heap every day. Keep a special bin for kitchen leftovers and tip them in once a week.
There is some argument about whether it is better to leave everything alone or to turn over the mixture occasionally. The compost heap must be allowed to ferment, so on the whole, leaving it to its own devices is probably better than messing with it too often. The biggest problem is getting at the rotted matter at the bottom, especially in plastic containers as the compost within gets very compacted and hard to dig out.
Patience is needed with a compost heap. It will take from three months to a year for everything to decompose fully. The smaller the ingredients, the quicker it will all rot, so cut up your vegetable remains clippings before adding them to the heap; think of it as making a soup. For the less patient among us, garden centres sell a compost accelerator. This acts almost like a yeast starter in bread or wine making. The traditional compost activator is urine, which has the virtue of being readily available, while chicken pellets are also good. When everything has decomposed, the compost should look like a very dark, crumbly, fibrous soil or humus. For those with sensitive noses, be reassured that proper compost has a lovely, rich smell and does not stink at all.
All plants need nitrogen, phosphates and potash, often sold together as NPK, the protein, fat and carbohydrates of the vegetable world. Nitrogen helps leaves to grow and promotes healthy green foliage. Phosphates are vital for healthy root development. Potash (another name for potassium) not only ensures better yields of flowers, fruits and vegetables, but also makes plants more drought and disease resistant. Other nutrients, such as magnesium, manganese and iron, are needed in smaller quantities, but are not as important.
Although chemical fertilizers can give a plant a big initial boost, they ultimately create soft, weak plants that are prey to pests and disease. Nor are they good for the soil, poisoning worms, bacteria and fungi, three elements vital for keeping soil healthy. Because of their solubility, fertilizers can find their way into the ground water, so polluting rivers, lakes and even the sea to disastrous effect, as has been found in farming areas all over the world.
By the standards of artificial fertilizers, the amounts of available nitrogen, potassium and phosphorus from organic matter – that is, matter that was once alive – is low. It still contains everything that the garden needs in a natural form.
For the growth promoting properties of nitrogen, use anything rich in protein, such as blood, fish and bone meal and even diluted urine. Bone meal is also a source of phosphorus and potassium, while seaweed is rich in potassium and trace elements, as is rock potash. Wood ash is the traditional good source of potash. If you feel your soil is naturally low in a particular element, add this to the compost heap in one of the forms above. As the hazards of using chemical fertilizers have become better known, garden centres are stocking up in all these natural alternatives, so they are readily available.
Manure can be the gardener’s best friend, although not quite as easy to find in suburbia as in the heart of the countryside. If possible, buy in bulk and be prepared to take delivery by the tonne – sharing with a few neighbours might be an idea. If the manure is fresh, leave it to cool down for about six weeks, with a plastic sheet over it as protection from the rain. Add some of it to the compost bin as an activator.
A good tonic for wilting plants is liquid manure. This is easily made. In a bucket, mix a shovel of manure with three times its volume in water. Stir it vigorously and pour on the plants.
DO NOT include: