Fish emulsion fertilizer is a liquid fertiliser made from fish waste — the parts of the fish left over after processing — broken down into a dark, strong-smelling liquid that plants absorb quickly. It has been used for generations because it works: it supplies nitrogen fast, adds trace elements and amino acids, feeds soil organisms, and is gentle enough that it rarely burns plants when diluted properly. It is one of the most useful organic liquid feeds for vegetables, and it has a place indoors too, with a little care about the smell. This guide explains what fish emulsion is, how to use it, how much to apply, and the rules that keep it safe.
Fish emulsion is not fish oil and not fish meal. Fish meal is the dried, ground solid, used as a granular fertiliser. Fish emulsion is the liquid, made by breaking fish waste down with enzymes or heat, and it is sold as a concentrate that you dilute in water before use. Its nutrient content varies by brand, but a typical analysis is around 5-2-2 NPK — high in nitrogen, modest in phosphorus and potassium — plus trace elements and organic matter. Because it is a natural product, the exact numbers vary from batch to batch, so always follow the label rate for the product you buy rather than a figure from a guide.
What fish emulsion does
Fish emulsion feeds plants in two ways. First, it supplies nitrogen quickly in forms plants can take up within days, which makes it useful for leafy growth and for reviving pale, hungry plants. Second, it feeds soil organisms: the proteins and amino acids in the emulsion are food for bacteria and fungi, which then release nutrients slowly over the following weeks. That dual action — a quick feed plus a slow biological effect — is why fish emulsion often greens plants up faster than a mineral feed and keeps them growing for longer than a single dose would suggest.
It is most useful for leafy vegetables and heavy feeders early in the season, for seedlings after their first true leaves, and for any plant that looks pale and nitrogen-short. It is less useful as a sole feed for fruiting plants late in the season, when they need potassium more than nitrogen — a high-nitrogen feed at that stage gives lush leaves and little fruit. For fruiting plants, use fish emulsion early for growth, then switch to a high-potassium feed such as seaweed or a tomato feed once flowers appear. See our fertilizing vegetables guide for the full seasonal routine.
How to use fish emulsion
Dilution. Fish emulsion is sold as a concentrate and must be diluted before use. A common dilution is roughly 15 ml (one tablespoon) per 4 litres of water, but rates vary by brand — some are 1:50, others 1:100 — so always follow the label on your bottle. More is not better: a stronger mix does not feed the plant faster, and it can burn roots and smell worse. Mix it in a watering can, stir well, and use it the same day.
On vegetables. Water the bed first so the soil is moist, then apply the diluted emulsion around the base of plants, using roughly 1–2 litres per square metre of bed. Apply every two to three weeks through the growing season for heavy feeders such as tomatoes, cabbage and lettuce. For seedlings, use half the label rate once the first true leaves appear. Do not apply to dry soil, and do not apply in hot sun — morning or evening is best. Wash all vegetables before eating, and do not apply fish emulsion to leafy crops within a few days of harvest.
As a foliar spray. Dilute the emulsion to half the soil-drench rate, strain it if needed, and spray leaves until lightly wet, top and underside, in the early morning or evening. Foliar feeding gives a fast green-up, because leaves absorb nutrients directly, but it is a supplement to soil feeding, not a replacement. Do not spray edible leaves close to harvest, and always wash produce before eating.
On houseplants. Fish emulsion works well on houseplants such as monstera deliciosa and golden pothos, diluted to half the label rate and applied monthly in the growing season at most. The smell is the main drawback indoors: it fades within a day or two, but use it when windows can be opened, and do not use it on plants in a room where the smell will be a problem. See our fertilizing houseplants guide for the indoor feeding routine.
On compost and soil. Diluted fish emulsion can be poured over a compost heap to add nitrogen and speed breakdown, and it can be used to charge biochar before the biochar goes into the soil — see our biochar for garden guide. It can also be used as a soil drench for lawns and shrubs, at the label rate, in spring and early summer.
The smell — and how to manage it
Fish emulsion smells, and there is no point pretending otherwise. The smell is strongest when the bottle is opened and when the emulsion is first applied, and it usually fades within a day or two outdoors. Indoors, it can linger longer. To manage it, dilute properly — a stronger mix smells worse — apply in the morning so the smell disperses during the day, water it in well so it soaks into the soil rather than sitting on the surface, and avoid using it indoors the day before guests arrive. Some brands are deodorised and smell less, though they usually cost more. If the smell is a problem, seaweed extract is a less smelly alternative, though it is lower in nitrogen. Store the bottle tightly closed, upright and cool, and keep it away from children and pets.
Common mistakes
The most common mistake is using it undiluted or too strong, which burns roots and smells far worse than a proper dilution. The second is applying it to dry soil, which also burns roots — water first. The third is using it as the only feed for fruiting plants late in the season, when they need potassium more than nitrogen. The fourth is applying it to leafy crops close to harvest without washing the produce. The fifth is using it in winter on plants that are not growing, which wastes the feed and can cause salt build-up. And the sixth is storing the bottle badly — open, warm or on its side — so it leaks, smells, or goes off. Fish emulsion has a shelf life, so check the date and replace a bottle that smells rotten rather than fishy.
Safety notes
Wear gloves when handling fish emulsion, and wash your hands before eating. Keep the bottle away from children and pets, and store it upright in a cool place. Wash all fruit and vegetables before eating, especially leafy crops, and do not apply fish emulsion to edible crops within a few days of harvest. Do not use fish emulsion on plants if you are unsure about allergies in the household — fish is a common allergen, and the emulsion contains fish proteins. If you are unsure about safe use, check your local extension service for advice.
Frequently asked questions
How do I dilute fish emulsion fertilizer?
Follow the label on your bottle — a common rate is roughly 15 ml (one tablespoon) per 4 litres of water, but rates vary by brand. Always dilute before use, never apply it undiluted, and use the mixed solution the same day. More is not better: a stronger mix burns roots and smells worse.
How often should I use fish emulsion?
Every two to three weeks through the growing season for outdoor vegetables, and monthly at most for houseplants, at half the label rate indoors. Stop feeding late in the season so plants harden off before winter, and do not feed plants that are not actively growing.
Does fish emulsion smell?
Yes, it smells of fish, most strongly when first applied, and the smell usually fades within a day or two outdoors. Dilute properly, apply in the morning, water it in well, and use deodorised brands or seaweed extract indoors if the smell is a problem.
Is fish emulsion good for tomatoes?
Yes, early in the season, for leafy growth. Once tomatoes start flowering, switch to a high-potassium feed for fruiting — too much nitrogen after flowering gives lush leaves and little fruit. Use fish emulsion for growth, then a tomato or seaweed feed for fruit.
Can I use fish emulsion on seedlings?
Yes, at half the label rate, once the first true leaves appear. Do not feed seeds or seedlings before true leaves — they carry their own food at first, and early feeding can burn young roots. See our seed starting mix guide for the seedling routine.