Almost every gardening problem that gets blamed on something else is a soil problem. Plants that sulk in a wet spring, beds that set like concrete in August, seedlings that never quite get going: the cause is usually under your feet rather than in the weather. The useful part is that identifying your soil takes about two minutes and costs nothing.
The hand test
The RHS is clear that the best way to tell what soil you have is to touch it and roll it in your hands. Take a handful from about a spade's depth, damp but not soaking, and work it between your fingers.
- Sandy soil has a gritty element. You can feel the grains, it falls through your fingers, and it cannot be rolled into a sausage shape.
- Clay soil smears, is sticky when wet, rolls easily into a long thin sausage, and can be rubbed to a shiny finish with a finger.
- Silt feels slightly soapy and slippery, and does not clump easily.
- Loam sits between them, holding together loosely and breaking apart when poked. The RHS calls it the gardener's best friend, and if you have it you should be quietly pleased.
There is a separate chemical test for chalk. Drop a lump of soil into a jar of vinegar. If it froths, the soil contains free calcium carbonate and is lime rich.
The other common approach is the settlement or jar test: half fill a jar with soil, top it up with water, shake it hard and leave it for a day. Sand drops out first, then silt, then clay in a fine layer on top, and organic matter floats. It is a useful cross-check on the hand test, though it takes rather longer than rolling a sausage.
What each soil needs
| Soil | Behaviour | What helps |
|---|---|---|
| Clay | Heavy and nutrient rich, holds water, drains slowly, compacts easily, cold and late in spring | Organic matter, to break the clay into crumbs and improve workability and warmth |
| Sandy | Light, free draining, warms fast, loses nutrients quickly | Organic matter to hold water and nutrients. Feeding may still be needed |
| Silt | Fertile, fine particles, compacts easily under foot | Organic matter to bind the particles into stable crumbs |
| Chalky | Alkaline, free draining, often shallow over rock | Choose plants that suit alkaline ground. You cannot practically acidify it |
| Loam | Balanced, workable, the one everyone wants | Keep adding organic matter, particularly where you crop annually |
Notice that the answer is the same for four of the five. Organic matter improves drainage in clay and water retention in sand, which sounds contradictory until you realise it is doing the same thing in both cases: building crumb structure so that the soil holds air and water in the right proportions. Compost, well-rotted manure and leaf mould all do it. There is more detail on the RHS soil types page.
How much organic matter, and how long
Vague advice to add compost is not much use when you are standing in a garden centre. Here is the arithmetic.
A mulch 5cm deep over one square metre needs 50 litres of material, because 1cm over 1m² is 10 litres. A standard 3m by 3m bed is 9m², so a 5cm mulch across it takes 450 litres, which is roughly eleven 40 litre bags of compost, or a little under half a cubic metre.
That is the number that makes people order in bulk. Bagged compost is convenient for containers and expensive for beds. A builder's bag of well-rotted manure or municipal green waste compost usually holds around a cubic metre and costs a fraction of the equivalent in bags.
Timescale next, and this is where honesty matters more than encouragement. One application will not transform heavy clay. What one application does is make this season noticeably better. Three or four annual applications produce a soil that is genuinely different to dig, and clay that has been mulched every autumn for five years is a pleasure rather than a chore. There is no shortcut, and nothing sold in a bottle changes that.
Soil pH
Separate from texture is chemistry. A simple pH kit costs a couple of pounds and tells you whether your soil is acid, neutral or alkaline, which decides what will grow well without a fight.
Most vegetables prefer slightly acid to neutral ground. Brassicas do better nearer neutral, which is part of the reason clubroot causes most trouble on acid soils. Potatoes tolerate more acidity than most crops, and blueberries and rhododendrons need genuinely acid conditions that most gardens cannot provide.
Two warnings. First, take samples from more than one spot: pH varies across a garden, particularly near old building rubble or a lime-mortared wall. Second, lime raises pH slowly and is very difficult to undo, so read the RHS guidance on pH and liming, follow the product's own rate, and retest a season later rather than adding more on a hunch. Acidifying an alkaline soil is harder still, and on chalk it is not realistically possible. Choosing suitable plants is the cheaper answer.
Practical habits that protect soil
- Stop walking on it. Compaction undoes everything else. Beds 1.2m wide can be worked from both sides without stepping on the soil, and boards spread your weight when you must.
- Do not dig wet clay. Working clay when it is saturated smears the structure and you will be undoing it for two seasons. Wait.
- Mulch in autumn. Spread organic matter on the surface and let the winter and the worms take it down. It is less work than digging it in and it does not disturb the structure you are trying to build.
- Keep the ground covered. Bare soil erodes, caps over in rain and grows weeds. A green manure over winter, or a mulch, keeps it working.
- Test once, then act for years. Soil type does not change. Once you know what you have, every future decision about crops, watering and drainage gets easier.
Once you know your soil, you can plan around it. Our garden planner lets you lay out beds and spacings to match, and our month by month sowing calendar covers the timing side of the same decisions.
This is general growing information rather than advice for a specific garden or a specific problem. Soil varies over a few metres, let alone a few miles, and the RHS pages on soil types, pH and improving soil carry the full detail if you want to go further.