Using your compost in the garden: the right amounts for each crop (vegetable patch, trees, lawn)

Print

Your compost is mature, harvested and perhaps sieved. How much should you use, and where? It's tempting to pour it generously everywhere, thinking it can't do any harm. In reality, compost needs to be measured out like any other input in the garden: according to each plant's needs, at the right time, and always mixed into the soil.

The quantities below are annual guidelines, expressed in kilos per square metre. We arrived at them by comparing the recommendations of several reliable guides. Where these sources differ, we have kept to cautious ranges: a little less every year is better than a lot all at once.

Young compost or mature compost: which use?

Before talking about amounts, you need to know what kind of compost you have in your hands.

• Young or semi-mature compost should only be used on the surface: as a mulch, around the base of trees and shrubs, on bare soil in autumn or between well-established crops. Because it is still active, it can harm young plants if it is dug in too early.
• Mature compost can be worked into the soil, but only near the surface: a light raking or hoeing is enough. It does its work in the top few centimetres of soil, and earthworms take care of the rest.

If you're unsure what stage your compost has reached, the tests in our guide How to tell if your compost is mature will help you decide.

In the vegetable patch: according to each vegetable's appetite

Not all vegetables have the same needs. They fall into three groups.

Hungry vegetables: 3 to 5 kg/m² per year

Tomatoes, aubergines, peppers, potatoes, squashes, courgettes, cucumbers, melons, leeks, celery, artichokes and sweetcorn. These are the ones that benefit most from compost. Some guides give a slightly lower range (3 to 4 kg/m²): stay at the lower end of the range if your soil is already rich.

Moderately demanding vegetables: 1 to 3 kg/m² per year

Carrots, beetroot, spinach, lettuces, beans, peas, parsley, asparagus.

Undemanding vegetables: little or no compost

Garlic, onions, shallots, radishes, turnips, lamb's lettuce, broad beans and herbs are quite happy with what remains in the soil after the previous crop. They can do without any added compost, although some guides allow a thin layer. Cabbages are classified differently depending on the source, either as undemanding or as hungry: a moderate amount is a good compromise.

Willy's tip

No scales in the garden? Remember this simple rule of thumb: a layer of compost about 1 cm thick corresponds roughly to 3 to 5 kg per square metre. That's the right amount for hungry vegetables. For moderately demanding ones, a thinner layer is enough.

When and how to apply it

• In autumn or late winter, spread on the surface and lightly raked in;
• in spring, between the rows, before mulching over the top;
• at planting time, at the bottom of the hole, covered with a little soil so that the roots reach it as they grow without being in direct contact with it.

Between rows of fruiting vegetables (tomatoes, cucumbers, peppers), a layer of compost about 2 cm thick can also serve as a nourishing mulch.

Fruit trees and bushes

For ongoing care, spread a layer of compost about 1 cm thick each year over the whole area beneath the foliage: allow 3 to 5 kg/m² for trees and 2 to 3 kg/m² for bushes (redcurrants, raspberries, blackcurrants). You can cover it all with straw.

At planting, mix about 20% compost into the soil in the hole, i.e. one part compost to four parts soil.

Lawns, hedges and flower beds

Lawns

When creating a lawn, before sowing, work 8 to 10 kg/m² of compost into the top ten centimetres of soil. For ongoing care, spread 1 to 2 kg/m² at the start of each spring, finely sieved so that it settles between the blades of grass.

Hedges

At planting, 8 to 10 kg/m² worked in to a depth of about fifteen centimetres. After that, 2 to 3 kg/m² every two years is enough, lightly raked in between the plants.

Flower beds

When creating a bed, 5 to 8 kg/m² worked in while digging. For maintaining perennials, there are two options: a layer of about 2 cm of well-matured compost around the plants in autumn, which also protects the crowns from the cold, or 3 to 5 kg/m² raked into the surface in spring.

Compost as mulch

Young or semi-mature compost makes an excellent mulch: it feeds the soil gradually, reduces evaporation and slows the emergence of unwanted weeds. On flower beds and in the vegetable patch, keep to about 2 cm of compost. Some guides recommend thicker layers, but compost is still a rich material: if you want a thicker mulch, top it up instead with dead leaves, straw or shredded woody material.

Two precautions: keep the mulch a few centimetres away from stems and trunks, and if possible cover the compost with a plant-based mulch, which protects it from rain and sun.

Mistakes to avoid

• Sowing or planting in pure compost. This is the most important rule: compost should always be mixed with soil. For your pots and seedlings, follow the recipes in our guide Making your own potting compost.
• Burying it deep. Compost works in the top few centimetres of soil. Digging it in deeply serves no purpose.
• Putting young compost in contact with seedlings or young roots.
• Overdoing the amount. Compost also supplies nutrients: beyond what the plants need, the surplus is likely to be washed away by rain instead of feeding your crops.

What compost really does for the soil

Compost is above all a soil improver: it feeds the soil more than the plant. It increases the organic matter content, helps the soil retain water, makes it better aerated and easier to work, and releases its nutrients slowly, over the months. Soil that regularly receives compost also attracts earthworms, whose role we explain in our guide The ecological role of earthworms. If your garden is short of them, our guide Reintroducing worms into the garden sets out simple methods, using our Eisenia compost worms.

Did you know?

A long-term field trial was launched in 1998: a cultivated plot receives compost made from biowaste and green waste roughly every two years. Between 1998 and 2011, the carbon stock in its surface layer rose from about 40 to 58 tonnes per hectare, whereas it fell slightly on the plot that received nothing. Depending on the treatment, 60 to 73% of the carbon supplied by the compost remained in the soil. These figures relate to an agricultural field and agricultural application rates, but they clearly show the lasting effect of compost on organic matter.

Key points

Hungry vegetables: 3 to 5 kg/m² per year. Moderately demanding vegetables: 1 to 3 kg/m². Undemanding vegetables: little or none. Fruit trees: 3 to 5 kg/m², fruit bushes: 2 to 3 kg/m². Lawn: 1 to 2 kg/m² each spring. And never sow or plant in pure compost.

In summary

Compost should be measured out according to the plants' needs: generously for hungry vegetables and fruit trees, more lightly for moderately demanding vegetables, lawns and hedges, and hardly at all for garlic, onions or radishes. Young compost stays on the surface as a mulch; mature compost is raked into the top few centimetres of soil. Mixed with soil, never used pure, and applied every year rather than all at once, it improves your soil for the long term, as long-term field trials confirm.

Related products

Best Seller

Vermicompost, Worm castings | 13L Bag

Resulting from the digestion of organic matter by earthworms.

£7.51 €9.00

Pre-order

245L Maze Rotating Composter with Double Chambers

Effortless outdoor composting

£173.09 €207.50

Compostys wooden composter | 305 litres

PEFC-certified spruce wood

£96.62 €115.83

Best Seller

Bokashi Confort Composter

14-litre capacity, available individually or as a set of 2

£34.06 €40.83

Other topics in the guide

Vermicomposting30 sheets →Bokashi24 sheets →EM micro-organisms26 sheets →