It is important to know your type of soil by broad definition in order to cultivate it correctly. The accompanying chart indicates the usual classifications, the characteristics by which they can be identified, their good and bad points, and treatments needed for their improvement.
A Quick Guide to Soils—Their Characteristics and Their Needs
|Type Of Soil||Identifiable Characteristics||Good Points||Bad Points||Treatments Needed For Improvement|
|Stony, gravel||Many small to large stones in thin layer of soil.||Good drainage from surface.||Dries out too quickly.
Hard to work.
|Remove larger stones that hinder working.
Break up ground to give more rooting depth.
Feed liberally with humus-forming organic matter.
Use slow-acting fertilizers for base feeding
|Sandy||Feels gritty to fingers.
Does not hold together when compressed.
Tends to be light in color.
|Light to work.
Warms readily for early cropping.
|Dries out quickly.
Loses soluble nutrient too readily.
|Add humus-forming organic matter liberally; with winter manuring, summer mulching.
Cultivate topsoil well ahead of growing season.
Correct acidity with ground chalk.
Use a seaweed soil conditioner annually.
|Silt||Feels silky when rubbed between finger and thumb.
Does not mold when squeezed.
|Fairly easy to work.
More fertile than sand.
Apt to cake at surface.
Dries out too readily.
|Work in humus-forming organic matter liberally.
Top-dress with clay or clay marl in winter.
Correct acidity with chalk or fine limestone dust.
Improve conditions with gypsum or powdered seaweed.
|Loams||Blends of sand and clay mainly.
Retains shape when compressed.
Smears the skin when rubbed.
Slightly gritty if a light loam.
Polishes and leave heavy smearing if a heavy loam.
Good to work.
|Respond readily to humus-forming organic matter, worked into the topsoil in autumn-winter.
Lime lightly to correct any acidity.
Otherwise, the best of soils for gardening.
|Clay||Feels sticky and plastic.
Retains shape when molded.
Leaves heavy smears on fingers.
Amenable to change.
|Heavy to work.
Dense, slow to warm up.
Cakes and cracks on drying out.
|Add gypsum to improve porosity in autumn/winter.
Add lime in any form in offsetting acidity.
Expose soil to weathering by rough deep digging or ridging in autumn.
Incorporate humus-forming organic matter liberally.
|Whitish subsurface soil, often with chalky or limestone lumps.||Adaptable for many lime-tolerant ornamental plants.||Excess alkalinity.
Poor fertility, hungry for organic matter.
Needs good management.
|Break up in depth without bringing fragments upwards, thereafter cultivate topsoil only.
Add humus-forming organic matter freely, especially peat, pulverized bark, strong manures, and mulches.
Give balanced fertilizers, acid-reacting sulphur, aluminum and ferrous sulphates, used judiciously, offset high alkalinity.
|Peat (Fen)||Rich brown to black color.
Spongy, fibrous nature, moist.
|Easy to work.
Ideal for lime-intolerant plants.
Apt to shrink in cultivation.
|Increase drainage, where water table is high.
Add ground limestone or chalk to reduce acidity.
Dress a sandy or silty light peat with marl.
Add actively decomposing organic matter.
Basic slag, bone meal, nitro chalk are useful fertilizers.
Soil forms at the surface under the action of weathering forces, the additions of organic materials and their subsequent mixing. Fertility is greatest at the surface, but extends downwards as the various components of the soil become more mixed and integrated.
Somewhat arbitrarily the more fertile surface layer is termed the topsoil and beneath its depth is the subsoil, though there is no sharp demarcation. A soil is brought into cultivation by breaking up the topsoil by digging, ploughing or rotavating.
This admits air, increases drainage, excites biochemical activity and releases fertility. It prepares the soil for sowing and planting. It enables us to make additions to the soil, such as organic matter, lime and fertilizers, for its amendment and enrichment.
Usually, cultivations are confined to the topsoil, sometimes referred to as the top-spit—a spit being the depth to which a spade blade is used.
Subsoil and Drainage
Subsoil begins where the soil color becomes lighter from an increasing lack of organic matter and is more mineral in nature. It is less fertile than the topsoil, and less aerated.
It receives the rains percolating through the topsoil, and these accumulate to saturation point and find a level known as the water table. This fluctuates according to rainfall and the ease with which water can move and drain away through the subsoil to springs, streams and rivers.
Plant roots grow downward, but can only anchor themselves well in the subsoil and take moisture from it, if it is sufficiently porous and well drained to avoid saturation, stagnation and a water table that does not persist either high or long.
Good drainage at subsoil level is vital to plant health and vigor. A simple check is to make a hole 60cm/24in deep at the low point of your ground, and watch the water table in the hole after heavy rain.
If little or no water drains in, there is good subsoil drainage. If the water level rises and sinks quickly below topsoil level, it is still satisfactory. If the water level rises high and drains only slowly, then provision for subsoil drainage should be made.
It is sensible and beneficial to prepare ground for gardening by digging with a sharp spade, kept free of clogging soil by periodic scraping, though a flat tined fork is lighter and easier to use on sticky heavy soil.
It not only admits air and light, helps drainage, and stimulates fertility, but gives the chance to remove perennial weed roots, to incorporate amendments and give a pleasing finish to the surface.
Timing is of some importance. It is desirable to give the soil time to reconsolidate before the growing season, and subject to conditions being favorable—not too dry and hard, not too wet-digging is best done at least a few weeks before sowing or planting time, in autumn or winter; though light soils can be left longer than heavy.
Simple or plain digging, which means turning and breaking up the topsoil one spit, or spade blade deep, is sufficient for soils already in cultivation or which have good porous and free-draining subsoils.
Take out a trench 30cm/12in wide and a spit deep; transfer this soil to the other end of the area to be dug, or, if large, mark out in two equal parallel areas, transfer the soil of the trench from one half to the opposite end of the other half, and work up one half and down the other, so that the excavated soil fills in the last trench of the adjacent half.
Turn the soil in strips or rows, inverting to bury any annual weeds. Organic matter can be strewn along the base of the trench as the soil is turned, or over the surface first and then turned in with the soil.
Where the soil is on the heavy side, and where the subsoil has been noted to be hard and relatively impervious, it is best to dig deeper by the system known as bastard trenching. The first trench is taken out 60cm/24in wide, and the soil placed aside to fill in the last trench.
This gives room to break up the exposed subsoil a spit deep with a fork, or if chalky or stony with a pickaxe or mattock. This subsoil is left in situ. It can usefully be dressed with amendments—limestone dust and grit if acidic; gypsum if very dense; or chopped turf or fibrous organic matter if very barren.
It is doubtful that full trenching which entails disturbing the soil to three spits deep is really rewarding save for special features such as permanent asparagus beds, borders, or sweet peas on stiff heavy soils.
As an alternative to simple digging on a sticky heavy clay, soil can be ridged. The ground is worked in 75-90cm/30-36in wide strips; the middle spadeful is turned forward, and then the left and right hand spadefuls are turned on top to form a ridge.
No attempt is made to break the clods down. Let exposed to the weather and the action of frost and thaw, the ridges are broken down to a workable tilth in spring.
Digging in itself will eventually lead to an impoverished, worn out soil. The greatest soil-builder-except possibly on peat-is humus formed from organic matter.
This can be incorporated with digging or used for mulching or topdressing soil occupied by plants.
Such materials as animal manures, poultry litter, peat, leaf mold, pulverized bark, spent hops, spent mushroom compost, weathered sawdust, shoddy, seaweed, and the prepared proprietary products are all eligible and good humus-formers.
A further invaluable source is compost made from the plant waste and debris, lawn mowings, leaves and organic kitchen waste regularly available from garden and home.
As it becomes available such material is heaped in layers of 10-15cm/4-6in thick, nicely moist but not saturated, dressed with an activator or accelerator of decomposition (QR, Garotta, Bio, Comprot are proprietary activators, or thin layers of fresh animal manure or nitrogenous fertilizer such as nitro-chalk), a sprinkling of topsoil and possibly a dusting of lime; repeated until the heap is complete.
Compost is best made in a container—a simple bin of wooden slats, openwork brickwork or stones, 90-120cm/36-48in square, and at least 120cm/48in high; a semi-rigid plastic round bin with aeration holes in the sides; or even an open-ended cylinder of PVC, polythene or large empty plastic, bag, punched with small holes in the walls, and arranged on wood stakes or a circle of pig-netting for supports.
Coarse and fine materials should be mixed when possible. Moisture-rich materials such as lawn mowings are best wilted for a day or two before being added. A cover against the rain and weather is essential to prevent over-wetting or cooling, by tented sheet polythene or corrugated sheeting.
The material soon heats up as it decomposes under bacterial and chemical attack, and shrinks in bulk. It can be turned top to bottom, sides to middle, to quicken decomposition further; or simply left until a crumbly, brownish, sweet earthy-scented mould that can be easily applied to the soil, in 12-16 weeks.
The need for lime arises on most cultivated soils from time to time. Lime is needed to counteract the natural tendency for soils to become more acid, and ensure the maximum availability of nutrients in the soil solution to plants.
It provides calcium, an essential plant nutrient; and most garden plants grow best in soils containing some free lime. Its presence encourages beneficial soil micro-organisms and earthworms, but discourages soil-borne diseases and pests.
It improves solid structure by flocculating clay particles into small granules, with benefit to aeration and drainage. The need for lime is best ascertained by topsoil testing; either with litmus test paper or an indicator fluid that shows the degree of acidity by its color reaction (PBI, Sudbury, and BDH Lime Testers are brands of Soil Testers for Lime).
When lime is needed, it is best applied in winter, after digging and organically manuring the soil, strewn evenly over the surface to be weathered in. Ground chalk or limestone remain active for 2-4 years; hydrated powder lime acts more quickly and may be applied in smaller amount.
Sowing and Planting
By late winter or early spring, the prepared soil is ready to be lightly forked and raked to a fine crumb-like tilth in a spell of fine weather when it is just beginning to dry.
This is the time to apply fertilizers, designed to provide plants with essential nutrients for their sustenance and growth.
Such fertilizers should be compounded to provide plants with a balance of the major nutrients they need, according to their kind; especially nitrogen for stem and leaf growth, phosphorus for root activity, flower and fruit formation and good ripening of growth, potash for healthy growth, disease resistance and color in flowers and fruits.
The appropriate or recommended amount should be raked in some days prior to sowing or planting. Seeds need only moisture, air and warmth to germinate, but the most influential factor is soil temperature. Seeds in cold wet soil are slow to germinate and often rot.
It is wise to wait until soil temperatures run at 15-18°C/60-65°F before sowing most seeds out of doors. The old adage has it ‘Sow dry, transplant wet’.
Once seeds are rooting they seek nutrients from the soil; and seedlings are ready for transplanting as soon as they are making true plant leaves.
They transplant best when young, and make good progress if they can then be set in soil nicely moist, and with their seed leaves at soil level.