Homemade plant food: free, natural fertilisers

Good soil, improved with compost each year, provides most of what plants need. But there are times — particularly for hungry crops and container plants — when a liquid feed makes a real difference. Making your own means you know exactly what's in it, and it costs nothing.

Why make your own plant feed

Bought liquid fertilisers are a significant recurring expense for keen gardeners, and most come in single-use plastic bottles. The ingredients — salts derived from mined mineral deposits or synthetic processes — work well, but they come with a material and financial cost. Making your own sidesteps both.

Homemade feeds are also part of a closed-loop garden: plants grow, you harvest the leaves or fruits, the waste goes back into compost or into a feed bucket, and the nutrients return to the soil. This is how productive gardens work over the long term without constant input from outside.

One honest caveat upfront: homemade feeds are not as precisely formulated as bought ones. You cannot know their exact nutrient content. For most purposes this does not matter — you are aiming to provide a useful supplement to well-prepared soil, not replace it. Keep that in mind and you will use them sensibly.

Comfrey and nettle feeds

These are the most useful homemade liquid feeds you can make, and both have been used by gardeners for generations with good reason. They are made from plant material that is genuinely rich in nutrients, and the resulting liquid — while deeply unpleasant to smell — is a real plant food rather than a myth.

Comfrey (Symphytum officinale or Bocking 14): comfrey is remarkable for its ability to draw minerals up from deep in the soil through its long taproot. Its leaves are particularly high in potassium, which makes comfrey liquid feed especially useful for fruiting and flowering plants — tomatoes, courgettes, dahlias, peppers, beans. If you have room in a corner of the garden, planting a clump of Bocking 14 (a sterile variety that won't self-seed everywhere) gives you a free, renewable feed source for years. You can cut the leaves several times a season.

Nettles (Urtica dioica): stinging nettles are high in nitrogen and make an excellent general-purpose feed, particularly useful for leafy crops, young plants and anything that looks pale and tired. They are readily available as a "weed" in most gardens and surrounding areas. Wear gloves when picking them — fresh nettles sting, though they lose this property once soaked or dried.

How to make a comfrey or nettle feed

The process is simple and requires only a bucket, some plant material and water. Allow three to five weeks for the liquid to develop.

1. Fill a bucket with comfrey or nettle leaves. Pack them in loosely. Roughly two-thirds full of leaves is about right. You can mix the two plants if you like — comfrey for potassium, nettles for nitrogen.
2. Weigh the leaves down. Use a heavy stone, a brick, or an old plate to keep the leaves submerged. Without this, the top layer of leaves rots in air rather than liquid, which is slower and less effective.
3. Fill with water and cover loosely. Rainwater is ideal; tap water works fine. Cover the bucket with an old piece of wood or cardboard — not sealed airtight, just enough to keep insects and debris out and to contain the smell somewhat.
4. Leave for three to five weeks. In warm weather the process is faster; in cool conditions it takes longer. The liquid is ready when it has turned dark brown and the leaves have largely broken down to a dark mush.
5. Strain out the plant material. Pour through an old piece of cloth or a sieve. The solid residue can go straight on the compost heap. Pour the liquid into an old bottle or container with a lid for storage.
6. Dilute before use. This concentrate is very strong. Dilute it to roughly the colour of weak black tea — typically somewhere between ten and twenty parts water to one part concentrate — before applying. Pour it around the base of plants, not on the leaves, and do not apply in hot direct sun.

Use the diluted feed every one to two weeks during the growing season on heavy feeders like tomatoes, courgettes, squash and dahlias. Leafy crops respond well to nettle feed in particular. Plants in containers, which cannot access nutrients from the wider soil, benefit more than those in the ground.

Compost tea and worm tea

If you have a compost heap or a wormery, you have two more sources of free liquid feed. These are generally milder than comfrey or nettle concentrate and can be applied more freely.

Compost tea: steep a cloth bag or old pillowcase of mature compost in a bucket of water for 24–48 hours. Remove the compost bag (empty the used compost back onto the heap), and apply the resulting liquid to the soil. It delivers soluble nutrients and a dose of beneficial microbial life. It works best used fresh — do not store it for more than a day or two. See our composting guide for how to produce good mature compost.

Worm tea (worm leachate): wormeries produce a dark liquid that drains from the bottom of the bin. This leachate is often described as a concentrated plant feed, and it does contain dissolved nutrients — but its exact composition varies depending on what your worms have been eating, moisture levels and how long it has sat. Dilute it generously (at least ten parts water to one) before using it on plants, and avoid applying it undiluted to roots. It is most useful as a soil conditioner and mild nutrient supplement.

Kitchen sources: what actually helps

Gardening advice online is full of enthusiastic claims for various kitchen scraps as plant food. Some of this is based in fact; a good deal of it is overstated. Here is a more honest assessment of the common ones:

• Used coffee grounds: contain a modest amount of nitrogen, some potassium and phosphorus, and organic matter. When worked into the soil or added to compost in reasonable quantities, they contribute to soil health over time. However, they should not be applied thickly as a mulch — in quantity they can compact and repel water, and heavy applications may raise soil acidity enough to affect sensitive plants. A handful around plants occasionally, or added regularly to the compost heap, is sensible. The idea that they repel slugs is not reliably supported.
• Crushed eggshells: are primarily calcium carbonate. Plants do need calcium, but most soils are not calcium-deficient, and eggshells break down very slowly — you would need an implausibly large quantity to have a measurable effect on soil calcium in a growing season. They are not harmful, and they add organic matter to compost over time, but do not expect them to fix blossom-end rot on tomatoes quickly. The answer to that problem is consistent watering.
• Banana peel: contains potassium and phosphorus. The popular advice to bury banana skins near rose roots or soak them in water for "banana water" is not meaningless — potassium does eventually leach into the soil — but the effect is modest and slow compared to using a comfrey liquid. Adding banana skins to the compost heap is a more practical route to returning their nutrients to the garden.

None of these kitchen materials are harmful in reasonable quantities, and they are genuinely better composted than sent to landfill. But they work best as part of a composting system rather than as standalone fertilisers applied direct.

Wood ash: useful with caveats

Wood ash from untreated wood (not painted, treated or composite materials) is a source of potassium and calcium, and it has a strongly alkaline effect on soil. Applied sparingly around potassium-hungry plants such as fruit trees, currants and gooseberries, it can be beneficial — particularly on neutral to acidic soils.

The caveats are important though. Do not apply ash to already alkaline soils, as making them more alkaline causes nutrient lockout (manganese, iron and other trace elements become unavailable to plants). Avoid applying around acid-loving plants such as rhododendrons, camellias, blueberries and heathers. Do not use ash from coal, treated wood or wood that has had paint or preservative on it. Store it dry — wet ash loses much of its potassium through leaching. Apply in moderation and work it lightly into the soil rather than leaving it in a thick layer.

When plants need feeding — and when they don't

One of the most common gardening mistakes is feeding out of habit rather than need. Plants that are growing in good, compost-enriched soil and showing healthy, well-coloured growth are unlikely to benefit from additional liquid feeding. You may be adding nutrients that are already abundant, potentially causing imbalance.

Plants that genuinely benefit from supplementary feeding are:

• Heavy-cropping vegetables — tomatoes, courgettes, squash, cucumbers, peppers — especially once they are carrying fruit.
• Plants in containers, which exhaust the available nutrients in their compost within weeks and have no access to soil below.
• Any plant showing pale, yellowing or poor growth that is not explained by disease, watering problems or root issues.
• Hungry flowers like dahlias, sweet peas and roses in active growth.

The foundation of a well-fed garden is not liquid fertiliser — it is good soil built up with regular additions of compost. Feed the soil, and the soil feeds the plants. Liquid feeds are a supplement for particular plants at particular moments, not a substitute for soil care.

• Comfrey or nettle leaves collected and packed into a covered bucket of water.
• Leaves weighed down and bucket left for three to five weeks, covered.
• Liquid strained and stored in a labelled, lidded container away from the house.
• Always diluted to the colour of weak tea before applying.
• Applied to moist soil around the plant base, not over leaves.
• Used on hungry crops and containers during the growing season.
• Kitchen scraps added to the compost heap rather than applied direct.