Soil Testing

Before you go and buy seeds and plants, you need to know your soil and what plants it will suit. Old or new, large or small, level or sloping, random or regular in shape, urban or rural in situation — and the two sides of many other coins can be tossed when it comes to defining a garden — all are happily subject to common guidelines of construction or reconstruction. But soil types can overlap all these variables.

If it is brand-new property, you will probably start with little more than builder’s rubble. More daunting is the really neglected garden, for just because it is there, with some sort of identity, however chaotic, it can bully you into backbreaking years of ineffectual weeding and thinning and a too tentative hand on shears and secateurs. See it from the outset as the pig’s ear it is and ruthlessly re-plan the basic layout before the search for any self-respecting plants or features that merit reprieve.

The established garden that is not entirely to the new owner’s taste should be approached far more respectfully. Unless the previous occupant has left detailed cultural notes on all the stock, it will take the best part of a year to note the habits of all the plants (in some cases even their identity) and so be in a position to decide what to keep, what to discard and what to move.


This is the first fundamental factor to consider. Until you know the nature of the soil you cannot expect to exploit its proficiencies or to counteract its deficiencies.

In type, soil is mainly chalky, sandy, clay or loam.

Chalky soil is light, lets water through easily but dries out quickly. Breaking up the subsoil will help moisture-seeking roots to find their way down. Topsoil can be enriched by frequent addition of farmyard manure and garden compost; peat will help it to retain water. Many plants and shrubs will thrive in this type of soil, but if you want to grow lime-hating plants such as rhododendrons, azaleas and heathers you will have to import masses of peat and confine such plants to a special section of the garden in an artificially raised bed. Sandy soil has much in common with chalky soil. It warms up quickly in spring, is well aerated but again will not hold water. Feed liberally and frequently in the autumn with well-rotted manure and compost well dug in. Mulch in summer with sedge peat or compost, watering well first if the ground is unduly dry.

Clay holds water too well and is consequently air-resistant, sticky, cold (little use for early crops) and hard work to dig or to fork. Deep cultivation in late autumn or early winter, with the addition of organic matter, will improve it. Drainage can be improved by adding sand and grit (weathered boiler clinker or cinders are useful) when the subsoil is forked over. (Never mix the subsoil with the topsoil.) Severe waterlogging can be cured by laying entrenched pipes, but a less costly solution is to dig drainage trenches running gently down to a soakaway pit. Each trench should be about 18 in. (say 45 cm) deep, filled to a depth of 6 in. (15 cm) with gravel, then topped with soil and, in the case of a lawn, grassed over.

The regular use of lime helps to break down a clay soil and make it less sour. Roses do particularly well on clay, especially if generous doses of sedge peat are added to the topsoil.

Loam, often found in mature gardens that have been well-nourished over many years, is the ideal soil. Its texture is determined by the proportion of sand to clay; the more sand the lighter the loam. If roughly two thirds is sand the soil will be open and porous, while its clay content acts to retain moisture. Loam also contains elements of lime and humus (the residue of decomposed organic matter and bacteria). If lime content is high, annual fertilising with manure or compost is necessary; if low, applications of lime will correct any over-acidity.

To take a sample of your soil collect about 1 lb (500 g) from different parts of the garden, mix and dry out in an airy place. Various soil-testing kits can be bought but not all are reliable, so it is worthwhile sending your sample to the nearest County Horticultural Office with a request for analysis and recommendations for treatment.

The acidity or alkilinity of the soil will be measured against the pH scale, of which the neutral point is pH 7:0. Above this the soil is alkaline; below it acid. Slight acidity is desirable, so between 6.5 and 7.0 is the reading to hope for, and 8-0 — indicating poor, devitalised soil — the one to dread.

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