Bulky organic matter
Two to five years of repetitionmoderate effortWell-rotted manure, garden compost or composted bark, spread thickly and repeatedly. The single intervention that helps every soil in this catalogue, for different reasons on each.
Improves structure on every soil type: it binds sand into crumbs that hold water and nutrients, and opens clay so air and roots can get through. It also feeds the soil biology that maintains the structure once it exists.
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What it changes
Horticultural consensusmoderate confidence
- Royal Horticultural Society: Improving soil
- James Hutton Institute — The James Hutton Institute: Soil organic matter and structure
Checked 2026-08-13
What it will not do: It will not change what the soil is made of. Clay with twenty years of compost in it is well-structured clay, not loam, and it will still be sticky in a wet February. Nor does it meaningfully move pH.
Manure must be well rotted. Fresh manure scorches roots and robs nitrogen from the soil as it breaks down, and manure from an unknown source can carry residues of persistent broad-leaved herbicides that damage potatoes, tomatoes and beans for several seasons.
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Worth getting right
Sourced guidancehigh confidence
- Royal Horticultural Society: Manure — aminopyralid contamination
Checked 2026-08-13
Worth doing on: Heavy clay, Sandy, Chalky and alkaline, Loam, Silty, Shallow over rock, Made ground and urban soil
Raised beds
Works straight awayhigh effortBuilding upwards instead of fighting the ground. The most dependable answer to bad drainage and shallow soil, and the only reliable one for a plant that needs a pH the garden does not have.
Lifts the root zone above the water table, so roots are in soil that drains even when the ground beneath does not. It also warms earlier in spring and gives rooting depth where there is rock or hardpan close to the surface.
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What it changes
Horticultural consensusmoderate confidence
- Royal Horticultural Society: Raised beds
Checked 2026-08-13
What it will not do: It does not drain the ground underneath. A raised bed on waterlogged clay is a container sitting on a puddle: it works because the roots are above the problem, not because the problem is gone. Beds under about 20 cm deep achieve very little of this.
Worth doing on: Heavy clay, Shallow over rock, Made ground and urban soil, Silty
Liming — raising pH
A difference within one seasonlow effortGarden lime raises the pH of an acid soil. A standard, evidenced practice with a modest and temporary effect, chiefly worth doing before brassicas.
Raises soil pH gradually, which improves the availability of most nutrients on an acid soil and substantially reduces the severity of clubroot in brassicas. The effect is measured in fractions of a pH point per application.
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What it changes
Sourced guidancehigh confidence
- Royal Horticultural Society: Liming soil
- Agriculture and Horticulture Development Board — AHDB: Soil pH and liming
Checked 2026-08-13
What it will not do: It is not permanent — rain leaches it out and the soil returns towards its natural pH over a few years, so it is a maintenance practice rather than a fix. It will not make an acid soil alkaline, and it cannot be undone once overdone.
Test before liming rather than after. Over-liming locks up iron and manganese and is far harder to correct than under-liming, and lime should not be applied at the same time as manure or nitrogen fertiliser because the combination releases ammonia and wastes both. Lime is caustic: keep it off skin and eyes.
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Worth getting right
Sourced guidancehigh confidence
- Royal Horticultural Society: Liming soil
Checked 2026-08-13
Worth doing on: Peaty and acid, Sandy, Heavy clay
Leaving the soil undug
Two to five years of repetitionlow effortMulching the surface and not turning the ground. Preserves the structure that organic matter builds, rather than breaking it apart annually.
Preserves the crumb structure, fungal networks and worm channels that give a soil its drainage and its air. Worms incorporate a surface mulch downwards without the structural damage that digging does.
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What it changes
Sourced guidancemoderate confidence
- Garden Organic — Garden Organic (Henry Doubleday Research Association): No-dig cultivation
- James Hutton Institute — The James Hutton Institute: Soil structure under cultivation
Checked 2026-08-13
What it will not do: It does not relieve existing deep compaction, which usually has to be broken once before a no-dig regime can maintain anything. Nor does it remove the need for organic matter — no-dig is a way of applying it, not a substitute.
Worth doing on: Heavy clay, Loam, Silty, Sandy, Made ground and urban soil
Green manures
A difference within one seasonlow effortSowing a crop specifically to be dug in or cut down, rather than harvested. Cheap organic matter grown in place, and cover on ground that would otherwise sit bare.
Adds organic matter without importing it, protects the surface from winter rain — which is what causes capping and nutrient leaching on light and silty soils — and, with a legume, fixes nitrogen. Deep-rooted types such as grazing rye break into moderately compacted ground.
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What it changes
Sourced guidancemoderate confidence
- Garden Organic — Garden Organic (Henry Doubleday Research Association): Green manures
Checked 2026-08-13
What it will not do: The quantity of organic matter a green manure adds is small compared with a barrowload of compost — its value is in covering ground through winter and in the roots, not in bulk. It also occupies the bed, which is the real cost on a small plot.
Do not let a green manure set seed, and choose one from a different family to the crop that follows. Mustard is a brassica, so it should never precede or follow brassicas on ground where clubroot is a risk.
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Worth getting right
Sourced guidancehigh confidence
- Royal Horticultural Society: Green manures
Checked 2026-08-13
Worth doing on: Sandy, Silty, Loam, Made ground and urban soil, Heavy clay
Coarse grit
Works straight awaymoderate effortHorticultural grit worked into a planting hole or a border. Genuinely useful at small scale, and routinely asked to do something it cannot.
Improves drainage locally where enough of it is used — a planting pocket, a raised alpine bed, a container mix. The grains hold pore space open that clay would otherwise close.
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What it changes
Sourced guidancemoderate confidence
- Royal Horticultural Society: Improving drainage
Checked 2026-08-13
What it will not do: It will not drain a clay garden. Grit only works at a proportion of roughly a third by volume, which for a vegetable bed is an unthinkable quantity; below that it makes the mixture denser rather than looser, in the same way that a little sand in clay produces something closer to concrete. Adding grit to the bottom of a planting hole in clay creates a sump that fills with water and drowns the plant.
Use coarse horticultural grit, not builder's sand or fine sand. Fine particles fill the gaps between clay particles rather than propping them apart, which is precisely the failure this intervention is blamed for.
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Worth getting right
Sourced guidancehigh confidence
- Royal Horticultural Society: Improving drainage
Checked 2026-08-13
Worth doing on: Heavy clay, Silty
Land drainage
Works straight awayhigh effortPerforated pipe in a gravel trench, falling to an outfall. The only intervention that removes water from a site rather than lifting plants above it.
Physically removes standing water from the root zone where the water has somewhere to go. It is the correct answer where a garden is genuinely waterlogged rather than merely heavy.
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What it changes
Sourced guidancemoderate confidence
- Soilscapes — Cranfield University, National Soil Resources Institute: Soil drainage classes
Checked 2026-08-13
What it will not do: It requires an outfall lower than the drain — a ditch, a soakaway in permeable subsoil, or a legal connection. A drain with nowhere to discharge to moves water a few metres and stops. It also does nothing for a soil that is heavy but not actually wet.
Discharging garden drainage into a public sewer or across a boundary is a matter of permission and, in places, of law. Check before digging rather than after, and be certain what is buried where.
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Worth getting right
Sourced guidancemoderate confidence
- Royal Horticultural Society: Garden drainage
Checked 2026-08-13
Worth doing on: Heavy clay, Made ground and urban soil
Surface mulch
Works straight awaylow effortA layer left on top rather than dug in. Different job from soil improvement, and often the more useful one on a soil that dries out.
Slows evaporation from the surface, so a droughty soil holds what it is given for longer. It also suppresses annual weeds and protects the surface from the impact of heavy rain, which is what causes capping.
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What it changes
Horticultural consensusmoderate confidence
- Royal Horticultural Society: Mulching
Checked 2026-08-13
What it will not do: It does not add water. Mulch applied to dry ground keeps it dry — the soil must be moist when the mulch goes on, which in practice means spring after rain rather than midsummer.
Worth doing on: Sandy, Chalky and alkaline, Shallow over rock, Loam
Deep beds and containers for root crops
Works straight awaymoderate effortSidestepping stones and shallow soil rather than removing them. The practical answer for carrots and parsnips on stony or shallow ground.
Gives a straight, stone-free run for a taproot to grow down. A forked carrot is a root that met an obstacle, and no amount of soil improvement removes the stones from a stony soil.
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What it changes
Sourced guidancehigh confidence
- Royal Horticultural Society: Growing carrots
Checked 2026-08-13
What it will not do: It does nothing for the rest of the garden, and it is not a general fix — it addresses one specific failure of one group of crops. Sieving stones out of an open bed is possible and rarely worth the labour, as more work upwards each year.
Worth doing on: Shallow over rock, Chalky and alkaline, Made ground and urban soil