Improving Your Soil

Real soil is not inert stuff, with no function other than to provide a moist, fertile foothold for plants. Although this may unfortunately be true of much of the world's fariland, smothered and spoiled over the years by repeated application of unbalanced fertilizers and indiscriminate poisons, natural soil is a vastly complex ecological system.

Your investigations will have revealed many of your own soil's unique properties-its pH, texture, warmth and moisture-retaining abilities, and the variety of living things that inhabit it (or depend on those that do).

During the exploratory process, you'll inevitably develop a feeling for its intrinsic nature and begin to see how you can best work with it. At the same time, you may well have identified some features that you'd like to improve or correct - or even adapt more drastically to accommodate plants with 'special needs'.

Even if the soil is healthy and wellbalanced, the demands of cultivation will place a burden on it that a wild place doesn't suffer. You're going to ask more of your soil, in terms of variety, productivity, and traffic, than a garden-sized patch of the wild could ever provide. It makes sense, then, to prepare the ground carefully in anticipation of these demands, and to plan for continued sustenance.

Digging
The first reason for digging the ground is to remove unwanted growth from the area before introducing what you want to grow. This ensures that all available light, water, and nutrients go into your chosen plants, and that they aren't overwhelmed by other species which are already flourishing because they're very much at home.

Clearing and weeding are not the only aims, though. Digging introduces air, which helps roots and soil fauna to breathe; it breaks up the ground to allow roots to penetrate more deeply and widely; this also helps to encourage rain water or irrigation water to soak in and spread underground. And while you're digging, you add and incorporate a variety of substances to enhance and fertilize the soil.

Disadvantages of digging:
Exposing new soil on the surface can accelerate drying-out and it can also bring deeply buried weed seeds to the surface where they'll be stimulated to germinate. Repeated digging can even do more hann than good to the soil structure as a whole. The basis of the "no-dig" philosophy is that, once cultivation is under way, regular mulching and surface-hoeing are all that's necessary to keep the soil - and your back - in good condition.

Breaking new ground
Unless the soil is already in exceptional condition, even when you plan to adopt the no-dig system, any "new" patch of ground must first of all be broken. Every single perennial weed should be removed now, taking care not to compact the already-dug soil by walking on it. At the same time, your soil analysis data will enable you to add whatever is necessary to remedy actual and potential problems by incorporating new material in sufficient quantities as you go along.

It pays to perform this groundbreaking ceremony thoroughly and carefully, to do it at the correct time of year, and in the best possible conditions. Generally speaking, heavy (clay) soil in temperate regions is best dug in the autumn, leaving the clods to be broken up by frosts. With lighter (sandy) soils, and in warmer climates, early spring is a better time. Sandy soil is rarely difficult to dig; clay soil can' be very heavy and sticky when wet or iron-hard when dry, so you need to catch the moment when it's moist enough to work but not so wet that it's impracticable.

Whatever the soil type, you will be adding a forkful of compost. strawy manure, or other mixed organic material for each spade-square section of ground you dig, so don't even think about starting to dig until you have collected enough of this material. The reward for all this hard work is that, if it's done right, it may never have to be done again.

Single-dig
Begin by digging an exploratory hole two spits (spade's depths) deep. Look to see whether there's a compacted layer beneath the first spit. If the compaction is limited to the upper spit, and there aren't too many deep-rooted perennial weeds, it may be possible to get away with merely single-digging the bed. Follow the plan shown on ** adding a fork-load of manure or compost to each hole before transferririg the next weeded spit into it.

Collect the extracted weeds as you go, to add to the slow compost heap. If you choose to take the risk, it is possible to cut down on hand-picking weeds by turning each spit of soil upside-down as you move it, thus burying the weeds. Don't expect this to be 100 per cent successful, however.

Double-dig
Double-digging is more thorough, more labourious, and a little more complicated than single-digging. If the soil is deeply compacted, or if there's a hard pan below the top spit where rain water has deposited fine soil particles, however, the effort will be repaid in full by the resulting improvements to both topsoil and subsoil, both in the long and short term.

The important rule is that subsoil and topsoil roust not be mixed or muddled up. A lazy way-which could be called one-and-a-half-dig-is to proceed as for single-dig but, instead ofjust shovelling compost into the hole, first deeply pierce and loosen the subsoil with a fork and then stir the organic material in, before covering it with the next spit of topsoil.

Proper double-digging is begun bytaking out a spit of topsoil from each of the first two squares, plus a spit of subsoil from the first only, and removing them to the diagonal corner. Now take the subsoil from the second square and drop it into the first hole, adding compost or manure at the same time. Cover this with topsoil from the third square, put subsoil from square three (plus organic material) into hole two, and so on.

Bastard trench
There are many more methods of digging, each with its champions and its critics. One that's worth mentioning is called bastard trenching. Here, the rule about not muddling topsoil and subsoil is reversed (see below), but there's still no getting away from the necessity of incorporating manure, compost, or organic refine.

Bastard trenching breaks the rules. Topsoil becomes subsoil, subsoil becomes topsoil. Burying topsoil helps to smother weeds, saving hand-weeding; exposed subsoil will soon be improved by mulching. On the way, the base layer is broken, stirred, and compost-enriched.

Whether single or double-digging, it pays to be systematic. For single-dig, remove the first spit of soil and take it to the opposite diagonal corner, where it will finally be used. All you need to do now is to dig each spit in turn, weed it, add compost, and leave it in the hole that was left vacant by the previous spit of soil.

When double-digging, you first remove two top spits and one bottom spit, as shown. The bottom spit from square 2 is weeded, corn posted, and heaved into hole 1. Then the top spit from square 3 is weeded and used to fill up hole 1. The pattern has now moved one square sideways, and is repeated at follows: bottom spit from square 3 goes into bottom of hole 2; top spit frown square 4 fills up hole 2.

No-dig methods
Once the soil has been broken and mixed with compost, worms and other organisms will start to work and multiply in the improved conditions you have created for them. One of the benefits of abundant, healthy, busy soil fauna is that they will take over the digging for you.

From now on, all that may be needed is a top-dressing of partly composted material, each autumn, together with sheet mulch. By the time the sowing season comes around, most if not all ofit will have been dragged under by earthworms. All you'll have to do is lightly hoe surface weeds (incorporating completed compost if you wish) before planting or sowing.

This is the basis of the classic no-dig method. A mulch helps to suppress weeds, thus removing one reason for digging; the organic material gradually disappears into the soil, thus removing another reason. If you're careful not to compact the ground by walking on it, the last reason for digging also disappears. Why it works and makes such good sense is that it's a perfectly natural system-there isn't a lot of double-digging going on in the natural world, after all!

But there are some natural diggers and stirrer of soil, such as moles and pigs, and therefore, nature being the economical system that it is, there are bound to be some plants that are adapted to grow on disturbed ground. Your vegetable patch, regularly disturbed by planting and removing crops. is the ideal habitat for these plants. You'll never do away with hoeing altogether, unless you can keep the entire surface of the plot blanketed with a light-proof barrier.

Sheet mulching
The principle here is to keep the whole bed in darkness, except where your chosen crops are permitted to emergeinto the light. Apply compost over the entire surface, and then cover it with a sheet mulch} - newspaper. cardboard, old carpet. or even heavvweight black plastic. Porous materials are best, however, since they allow rain water arid air to penetrate, although, in high latitudes and especially with clay soils,

Clear plastic can help to speed up spring warming. Underneath, the worms will chew away happily, mixing the compost in, and you can simply cut slits in the sheet mulch to insert your seedlings. This way, you can encourage natural soil improvers at the same time as getting a crop.

If double-digging is done - to break up a compacted layer of subsoil, work in plenty of compost as you go along; if not too weedy, the top spit might even be simply dropped upside-down on top of the already prepared subsoil.

Living compost
Green manures and cover crops do the same sort of job, but in two stages. While they're growing, they make dense ground cover round cover that shades out seedlings already present and prevents new seeds from reaching the ground. Before they go to seed themselves, you can either cut the tops off, leaving their widespread roots to add organic matter, dig the whole crop in as "green manure", or pull them up and compost them separately.

Some green manures, such as mustard, can be left in place to be killed by frost, but they'll naturally have set seed in the meantime. They are useful, however, when you want to keep a patch of ground "in hand" for more than a year, while steadily improving its condition

Selecting green manures
When selecting green manures, it's important to choose an appropriate one. The grass family tends to have widespread roots, and so is useful for penetration; Annual rye does a particularly goodjob in this respect. In temperate regions, winter hardiness is important because this allows a cover crop to stand through the winter, when the ground might otherwise be left idle.

Many of the best plants to use for green manures are those of the pea and bean family, called legumes.

Perennial legumes
The roots of leguminous plants - clovers, vetches, peas, beans, lupins, and many others - have the ability to grow lumps called nodules. These nodules shelter specific bacteria, which have the rare talent of being able to take nitrogen gas from the air itself and turn it into a chemical form that is readily available to plants.

Although nitrogen gas makes up the greater proportion of air, plants cannot make use of this element unless it's fed to their roots in some chemical compound form, such as nitrates (which are breakdown products of proteins). Having nitrogen-fixing bacteria cuddled around their roots gives legumes a distinct advantage over other, plainly rooted plants. They can, in fact, flourish in places which are not fertile enough for many other plant species.

One benefit to the gardener is thefact that legumes can be grown in poorsoil. An even greater potential benefit isthat legumes can be grown to improve fertility. Whereas most plants, when they're dug into the soil they grew from, merely put back what they already took out, legumes put back more available nitrogen than was there to begin with. Leaving perennial legumes in situ for more than one season steadily enriches the soil.

Legume inoculants
Legumes aren't always naturally well endowed with nitrogen-fixing bacteria. If the soil is deficient in this respect, they won't grow nodules to house them. It's easy to see whether leguminous plants have root nodules by simply pulling one or two up and looking for obvious pinkish-white lumps.

If your legumes have few nodules, or none at all, you can get things started by buying the bacteria, under the name Rliizobiuni, from a specialist supplier, and adding them to the soil. This only needs to be done once, and is very cheap. The easily obtained Rbizobium strains will cohabit happily with peas and beans hut, if you're growing clover, make sure that the Rhizobium you buy is compatible with it.

Soil inoculants
Other nitrogen-fixing bacteria also live independently in healthy soil. Among them are the type called Azotobacter. Adding Azotobacter at the saint time as sowing seed has given increased yields of many different commercially grown crops. If you have inherited an impoverished or otherwise abused patch of land, it might benefit from inoculation with Azotobacter.

Dynamic accumulators
Legumes are very special because they add new nitrogen to the soil. Other plants can help to concentrate - or accumulate - other elements, by making extra demands on the soil for these elements in order to use them in building leaf and stern tissue. They are, in a sense, mineral prospectors. If they are allowed to grow in a particular spot, and then are pulled tip. the minerals they've collected can be transferred from where they grew to a place where they're needed. There are two obvious advantages to be gained from using dynamic accumulators: to extract excess minerals and to add extra minerals.

In addition to this simple benefit. however, there is a further and more sophisticated advantage to be got from growing dynamic accumulators. Just as the legume bacteria "fix" raw atmospheric nitrogen into compounds that other plants can use, so some dynamic accumulators are able to "fix that other plants can use, so some dynamic accumulators arc able to "fix" other raw elements to create mineral compounds that enable less-talented plants to make use of these elements - to pre-digest them, as it were.

Trace elements
Plants can make carbohydrates from air and water, using sunlight energy. In order to snake protein, however, they need a supply of nitrogen (N), plus phosphorus (P) and potassium (K), together with sulphur (S). This is why the N:P:K ratio is so important in assessing fertility (sulphur is rarely deficient in soil).

The wide variety of enzymes and other proteins that plants need in order to develop properly, however, also requires a whole spectrum of other elements, though they're only needed in minute amounts. These are known a trace elements, and they include such substances as manganese, chromium, and copper, which may even be toxic in high concentrations but which, nevertheless, must be present as "traces" for healthy growth (and food value of crops).

This is one sound reason for using natural rock flours (rather than synthetically manufactured NPK compounds), which contain a variety of trace elements in addition to the N, P, and K. Dynamic accumulators arc also useful for either removing or adding trace elements.

Seaweed
Among the wide range of possible additives, seaweed deserves a special mention. It is a dynamic accumulator, although not one that you'd actually grow in your garden. It contains less nitrogen and considerably more potassium than farmyard manure, and provides a very wide spread of trace elements and minerals. When you apply seaweed to your garden, you are in effect assisting the return of essential minerals from the oceans to the land. But there's a great deal more to seaweed than minerals.

Seaweeds contain a wide range of organic substances, including hormones and amino acids, which improve the growth of other plants. As well as promoting growth, they improve uptake and use of nutrients and even increase resistance to pests and diseases.

Fresh seaweed (if you can get it, and if it isn't contaminated with oil, radioactivity, sewage, or heavy metals) can be used as a mulch or added to the compost heap. Dried and powdered, it becomes a wonderfully balanced natural fertilizer. Although it's quite expensive, only ?oz is needed per square yard (70g/sq m). Powdered seaweed also makes good compost activator. Liquid manures based on seaweed are the ideal foliar feed, with all the properties listed above.

Calcified seaweed is a type which resembles coral, because it builds a limey skeleton. It's a marvellous way to add fertility and slow-release lime in one easy stage.

Adjusting pH
The optimum all-round pH is somewhere around 6, which is best for vegetables in general. This is slightly on the acid side, and ought to follow naturally from regular composting.

If the soil is quite acid to begin with, however, or if lime-loving plants are to be encouraged, some alkaline substance can be added to correct this. The ideal slow source of lime, which will continue to maintain a constant pH for years after a single treatment, is calcified seaweed, although the ethics of seabed damage done while harvesting it are open to question.

Similar results (but without the added organic benefits) can be got from dolomite, ground limestone, or chalk, which can be added just before planting or sowing. Clay soils require more added alkali to raise pH than sandy ones. Lowering pH is more difficult than raising it, so check pH frequently to make sure you don't overcorrect.

Although adding lime in a more drastic way (as quicklime or slaked lime) has in many regions been adopted as standard farming practice, it is also said to make farmers richer, but their heirs poorer. This observation might be due to the fact that lime and earthworms don't mix happily, and it's the worms which will succumb.

Chalky soils may have a pH that's ideal for growing clover, but is too high for general purposes. There are three truly natural ways of lowering pH, but they all take a little time. Improving drainage will help by taking away rainwater, which leaches out chalk. Paradoxically, drainage can help to correct acid conditions, too, by allowing air in to tip the balance in favour of aerobic decomposers rather than anaerobic ones, which cause acidity.

Adding compost will, in time, also balance out the soil pH. The third alternative is to grow a dynamic accumulator of calcium, and then remove it. All these processes can be combined, to speed things up. As a last resort, if the soil is seriously alkaline (pH above 8), you could add gypsum, or sulphur in the form of "flowers of sulphur" 4oz/sq yd (140g/sq m) on sandy soil, twice as much on clayl.

Really difficult soils
Most of the strategies in this section are directed toward conditioning the soil for growing food plants. Ornamentals, after all, can be freely selected to fit your garden, whereas vegetables tend to be cosmopolitan species with specific requirements regardless of where they're planted. Three extremely difficult types of soil for vegetable growing arc deep sands, chalk, and black vertisols.

Sands allow water to run straight through, chalk is alkaline and physically difficult, and deep-crack clays can be impervious to water, except where open cracks allow it to run away uselessly. One way around such serious problems is to create a vegetable patch in the garden that is not of the garden.

On pure sand, it is possible to dig a pit and line it with plastic sheeting. This container can then be filled with compost (or any soil you like) as a growing medium. On chalk and difficult clay soils, probably the most sensible solution is to create raised beds.