Most garden advice assumes you know what you are working with. Plant labels say "well-drained soil" or "acid-loving" as though everyone can look at a bed and tell. You can find out in an afternoon, with a jam jar and a couple of things from the kitchen cupboard, and the answer changes what you plant and what you add for years afterwards.
Two properties matter more than anything else: texture, which is the mix of sand, silt and clay, and pH, which is how acid or alkaline the soil is. Texture decides how water and air move. pH decides which nutrients your plants can take up. Both are testable at home.
The jar test: what your soil is made of
Soil texture comes down to the proportions of three particle sizes. Sand is the largest, drains fast and holds little. Clay is the smallest, holds water and nutrients tightly and drains slowly. Silt sits between them. The mix determines nearly everything about how a bed behaves.
The jar test separates them by weight, and it costs nothing.
What you need
A straight-sided glass jar with a lid, ideally tall and narrow. A trowel. Water. A drop of washing-up liquid. A ruler.
How to do it
- Take a representative sample. Dig 15 to 20 cm down in four or five spots around the bed, take a handful from each, and mix them together. One hole tells you about one hole.
- Clean it up. Remove stones, roots, worms and anything that has not broken down. Break up lumps with your fingers.
- Fill the jar about a third with soil, then top up with water to roughly three quarters, leaving air at the top.
- Add one drop of washing-up liquid. This stops the clay particles clinging together, which is what makes the layers readable.
- Shake it hard for two minutes. Longer than feels necessary. Every lump has to come apart.
- Set it down and leave it. Do not move it again.
Reading the layers
The particles settle by weight, largest first.
- After one minute: mark the top of the bottom layer. That is sand.
- After two hours: mark again. The band above the sand is silt.
- After two days: mark the final level. The top band is clay. Organic matter floats or sits on the surface, and is not part of the calculation.
Measure each band, measure the total, and turn each into a percentage. Then read off what you have.
- Sandy soil: roughly 70 per cent or more sand. Water runs straight through, nutrients wash out with it, the bed dries out days before its neighbours and warms early in spring.
- Clay soil: roughly 40 per cent or more clay. Holds water and nutrients well, drains slowly, sets hard when dry and turns sticky when wet. Late to warm in spring.
- Silty soil: a high middle band. Holds moisture well, feels smooth and floury, compacts easily underfoot.
- Loam: roughly 40 per cent sand, 40 per cent silt, 20 per cent clay. Holds water without waterlogging, drains without drying out. This is the one everything else is measured against.
- Sandy loam: a loam leaning toward sand. Drains freely, warms early, easy to work, needs feeding and watering more often. Good for root crops, herbs, Mediterranean plants and anything that resents wet feet.
The quick check that needs no jar
Take a handful of damp soil and squeeze it.
If it falls apart as soon as you open your hand, it is sandy. If it holds the shape of your fist and you can roll it into a sausage and bend that into a ring without it cracking, it is clay. If it holds together but crumbles when you prod it, you have loam and you are lucky.
This tells you in ten seconds what the jar tells you in two days. The jar gives you proportions; the squeeze gives you a direction.
Testing pH at home
pH runs from 0 to 14, with 7 as neutral. Below 7 is acid, above 7 is alkaline. Most garden plants are happiest between 6.0 and 7.0, where the widest range of nutrients stays available.
The reason pH matters is not that plants dislike the number. It is that the number controls availability. In alkaline soil, iron and manganese lock up chemically, and plants show deficiency symptoms while standing in soil that contains plenty of both. Feeding does not fix that. Correcting pH does.
The kitchen cupboard test
This tells you direction, not a number, and that is often enough.
Take two small samples of soil. Into the first, pour a little vinegar. Into the second, add a splash of water to make a paste, then a spoonful of baking soda.
- The vinegar fizzes: your soil is alkaline. Vinegar is acid, and it is reacting with lime in the soil.
- The baking soda fizzes: your soil is acid. Baking soda is alkaline, and it is reacting with the acidity.
- Neither fizzes: your soil is somewhere near neutral, which is where most people want to be.
The reaction is quiet, so watch closely rather than expecting foam. Test in two or three spots. Soil pH varies across a garden, and it rises near walls and old paths where builders' rubble and mortar were left behind.
When to buy a test instead
If the cupboard test tells you the soil is strongly acid or strongly alkaline, and you plan to do something about it, get a number. Amending blind wastes material and can overshoot.
A paper strip kit is cheap and gives you a reading within half a point, which is enough for garden decisions. A probe meter is convenient but the inexpensive ones drift and respond to moisture as much as to acidity, so treat a probe reading as a suggestion. For a new plot, or before planting a hedge or fruit trees you intend to keep for decades, a laboratory test through a garden centre or agricultural office is worth the modest cost, because it reports nutrient levels and organic matter as well.
What the results mean for what you can grow
Acid soil, below about 6.0. Rhododendrons, azaleas, camellias, blueberries, heathers and most conifers are at home. Brassicas struggle, and clubroot is more of a problem. Many vegetables grow below their potential.
Neutral soil, 6.0 to 7.0. The widest choice. Most vegetables, most fruit, most ornamentals and most lawn grasses want to be here.
Alkaline soil, above about 7.5. Lavender, rosemary, thyme, clematis, lilac and many Mediterranean plants do well. Acid lovers will not, and no amount of feeding will change that. Iron deficiency showing as yellow leaves with green veins is the standard symptom on chalky ground.
The practical conclusion is worth stating plainly: it is easier to choose plants that suit your soil than to change your soil to suit your plants. Shifting a whole bed by a full pH point is a project of years.
Simple amendments that improve poor soil
For any soil
Organic matter is the one amendment that helps every soil type. Compost, well-rotted manure, leaf mould. In sandy soil it holds water and nutrients that would otherwise drain away. In clay soil it opens up the structure and lets water and air move. Spread 5 to 8 cm over the surface each autumn and let the worms take it down, or fork it lightly into the top layer.
You cannot overdo this within reason, and it is the single most useful thing you can do for a bed.
For clay
Organic matter, repeatedly. Coarse grit or sharp sand can help drainage, but only in quantity: a small amount of fine sand mixed into clay moves it toward something closer to concrete. If you add sand, make it coarse and make it plenty, or leave it out and use compost instead.
Avoid working clay when it is wet. It compacts under boots and spade and takes a season to recover. Raised beds are often the faster answer on heavy clay.
For sand
Organic matter, again, and more often, because it breaks down faster in a well-aerated soil. Mulch the surface to slow evaporation. Feed little and often, since nutrients wash through quickly.
To raise pH, making soil less acid
Garden lime, applied in autumn or winter so it has time to work. Follow the rate on the bag against your soil type, since clay needs much more than sand to shift the same amount. Do not apply lime and manure at the same time, as the combination releases nitrogen as ammonia and wastes it.
To lower pH, making soil more acid
Harder, and slower. Elemental sulphur is the usual route, and it works over months as soil bacteria convert it. Composted pine needles and ericaceous compost shift things gently. On chalky ground, growing acid lovers in containers of ericaceous compost is the realistic option.
Container soil is a separate question
Everything above concerns ground soil. A pot is a closed system with its own rules: the mix has to drain fast enough not to drown roots while holding enough water to last between waterings, and it loses structure after a year or two of watering.
Garden soil in a pot compacts and waterlogs, which is why potting mixes exist. If you are putting plants into containers, our guide to choosing the right potting mix covers which mix suits which plant, and when and how to repot covers the signs that a plant has outgrown what it is in.
Putting it together
Run the jar test once. Soil texture does not change unless you change it, so the result is good for as long as you garden that plot. Test pH every couple of years, and again after any serious amendment.
Write the results down somewhere you will find them. Knowing you have a sandy loam at pH 6.5 turns most planting decisions into simple ones, and it explains failures that otherwise look mysterious.
Soil tests tell you about the ground. They do not tell you what is wrong with a particular plant standing in it, and the symptoms overlap: iron deficiency from alkaline soil, nitrogen shortage, overwatering in heavy clay and early root rot can all present as pale or yellowing leaves. If a plant looks wrong after you have tested the soil, photograph it in Gardenix. The app names the most likely cause with a confidence level, gives a health score from 0 to 100 and a step-by-step plan, which is quicker than working through the possibilities one amendment at a time. Your first 3 scans are free.