Natural fertilisers are fertilisers from plant, animal or mineral sources — compost, manure, blood meal, bone meal, fish emulsion, seaweed and wood ash — used to feed plants without synthetic chemicals. They work differently from synthetic fertilisers: they release nutrients slowly as soil organisms break them down, they feed the soil as well as the plant, and they improve soil structure at the same time. This guide covers the main natural fertilisers, what nutrients each one supplies, how to use them, and the mistakes to avoid.
The first thing to understand is what plants need. Plants need three main nutrients: nitrogen (N) for leafy growth, phosphorus (P) for roots and flowering, and potassium (K) for fruiting and general health, plus smaller amounts of calcium, magnesium, sulphur and trace elements. Natural fertilisers vary in what they supply: some are rich in nitrogen, some in phosphorus, some in potassium, and some supply a little of everything. That is why it helps to know what your soil needs before you feed it — a soil test tells you more than guessing, and our soil pH testing guide explains how to check. If you are unsure what your soil needs, check your local extension service for a soil test. Compost is the foundation of natural feeding, and our composting basics guide explains how to make it.
Compost and manure
Compost is the most important natural fertiliser, and it is also a soil improver. It supplies a little of every nutrient, slowly, and it improves soil structure, water holding and soil life all at once. Work a 5–8 cm layer of compost into beds each year, or spread it as a mulch and let worms pull it down. Well-rotted manure — from horses, cattle, sheep or chickens — is richer than compost, especially in nitrogen, and it also adds organic matter. Use only manure that has rotted for several months: fresh manure can burn plants, carries weed seeds, and can carry pathogens. Never use fresh manure directly on edible crops, and never use manure from dogs or cats, which can carry pathogens that affect humans. Chicken manure is very rich in nitrogen and must be well rotted and used sparingly, or it will burn plants. Compost and manure are slow feeds: apply them in autumn or early spring, and let soil life release their nutrients over months.
Meals: blood, bone and fish
Blood meal is dried blood, and it is one of the richest natural sources of nitrogen — it pushes leafy growth fast, so use it sparingly on leafy crops such as lettuce and brassicas, and avoid it on fruiting crops where it encourages leaves at the expense of fruit. Bone meal is ground bone, rich in phosphorus and calcium, and it is best for root development and flowering: mix it into the planting hole for bulbs, roses and fruit trees, and for root crops. Fish, blood and bone is a balanced meal that supplies all three main nutrients in moderate amounts, and it is a useful general feed. Fish emulsion is a liquid made from fish waste, rich in nitrogen with some phosphorus and potassium, and it is a good quick liquid feed during the growing season. All meals should be worked into the soil or watered in, not left on the surface, and kept away from pets — dogs in particular are attracted to blood and bone meal and can be made ill by eating it. Store meals in sealed containers out of reach of children and pets.
Seaweed, wood ash and other natural feeds
Seaweed meal or liquid seaweed extract supplies potassium and trace elements, and it also contains plant hormones that may stimulate root growth — it is a useful general tonic, especially for fruiting plants and for plants under stress. Use it as a liquid feed every few weeks during the growing season. Wood ash from untreated wood supplies potassium and calcium and raises soil pH, so use it only on acidic soil and only in small amounts — a handful per square metre — and never use ash from treated wood, painted wood or coal, which can contain harmful chemicals. Epsom salts (magnesium sulphate) supply magnesium, and they help where soil is deficient in magnesium — our epsom salt in garden guide explains when to use them — but do not use them routinely without a soil test, because excess magnesium harms soil structure. Eggshells supply calcium slowly as they break down; crush them finely and mix them into the soil or compost. Coffee grounds supply a little nitrogen and organic matter; our coffee grounds in garden guide covers their use. None of these is a complete fertiliser on its own — they are supplements to compost, not replacements for it.
Liquid feeds: compost tea and others
Liquid feeds give a quick boost during the growing season, when plants are growing fast and need nutrients now. Compost tea — water in which compost has been steeped — supplies nutrients and beneficial microbes; our compost tea guide explains how to make it. Liquid seaweed and fish emulsion are bought liquid feeds that can be diluted and watered onto soil or sprayed onto leaves. Use liquid feeds every two to three weeks during the growing season, watering them onto the soil around plants rather than onto leaves in strong sun, which can scorch them. Do not overuse liquid feeds: they are a supplement, not a substitute for soil feeding, and too much liquid nitrogen produces soft, lush growth that attracts aphids and is vulnerable to frost. The compost ratio calculator helps with compost, and our organic gardening guide covers the wider system of natural feeding.
How to use natural fertilisers well
Feed the soil, not just the plant. Apply compost and manure in autumn or early spring, so soil life has time to work them in before the growing season. Apply meals at planting time, mixed into the soil where roots will find them. Use liquid feeds during the growing season for a quick boost. Feed lightly and often rather than in one heavy dose, because heavy rain leaches nutrients and excess fertiliser harms soil life and pollutes water. Watch your plants for signs of deficiency — pale, yellowing lower leaves often mean nitrogen is low, purple tints can mean phosphorus is low, and poor fruiting can mean potassium is low — but confirm with a soil test before adding large amounts of any one nutrient. Keep records of what you fed, when, and how plants responded, so you learn what your soil needs. And remember that natural fertilisers work slowly: compost feeds over months, not days, so do not expect instant results.
Common mistakes
The most common mistake is using fresh manure on edible crops, which can burn plants and carry pathogens — always use well-rotted manure. The second is over-fertilising, even with natural fertiliser, which harms soil life and pollutes water. The third is using blood meal on fruiting crops, which pushes leaves at the expense of fruit. The fourth is using wood ash on alkaline soil, which raises pH further. The fifth is leaving meals on the surface where pets can eat them. The sixth is relying on a single supplement, such as eggshells or coffee grounds, as if it were a complete fertiliser — it is not. And the seventh is feeding without a soil test, so you add nutrients the soil already has and miss the ones it lacks. Test first, feed lightly, and let compost do most of the work.
Frequently asked questions
What is the best natural fertiliser?
Compost, because it supplies a little of every nutrient, improves soil structure and water holding, and feeds soil life. Well-rotted manure is also excellent. Meals, seaweed and liquid feeds are useful supplements, but none replaces compost as the foundation of natural feeding.
Can I use fresh manure in the garden?
No, not directly on plants or edible crops. Fresh manure can burn plants, carries weed seeds and can carry pathogens. Compost it for several months until it is dark, crumbly and smells like earth, then use it. If you are unsure, check your local extension service for advice on safe manure use.
How often should I feed plants naturally?
Apply compost and manure once or twice a year, meals at planting time, and liquid feeds every two to three weeks during the growing season. Feed lightly and often rather than in one heavy dose, and adjust to what your plants and soil test tell you.
Is wood ash good for the garden?
Wood ash from untreated wood supplies potassium and calcium and raises soil pH, so it suits acidic soil in small amounts — a handful per square metre. Do not use it on alkaline soil, and never use ash from treated wood, painted wood or coal. Check your soil pH first with our soil pH testing guide.
Do natural fertilisers work as fast as synthetic ones?
No. Natural fertilisers release nutrients slowly as soil organisms break them down, so they feed over weeks and months rather than days. Liquid feeds such as compost tea and fish emulsion act faster, but the main benefit of natural feeding is long-term soil health, not instant growth.