Plant Library
Types of fertiliser: organic, synthetic, slow-release + NPK
The complete guide to types of fertiliser — organic vs synthetic, NPK explained, granular vs liquid vs slow-release, with UK + US brand picks.
Types of fertiliser: organic, synthetic, slow-release + NPK
Fertiliser confuses new gardeners because the shelf at any garden centre has 40 products with NPK numbers that look randomly chosen. They are not. The numbers tell you what each product is for, and once you can read them every label makes sense in 5 seconds. This guide covers the main types of fertiliser — organic vs synthetic, granular vs liquid vs slow-release — with the NPK ratios you should reach for in each garden situation, plus current UK and US brand examples (verified still on shelves in 2026 via current retailer listings).
Pick the right feed for your plant: Photograph what you're growing in Growli and we recommend the fertiliser type, NPK ratio, and application schedule for that specific plant.
NPK explained
Three numbers on every fertiliser label. NPK = Nitrogen, Phosphorus (as P₂O₅), Potassium (as K₂O), all by percentage of weight.
- Nitrogen (N) — leaf and stem growth. High-nitrogen feeds (lawn fertilisers, foliage-plant feeds, leafy-green feeds) drive lush green growth.
- Phosphorus (P) — root development and flowering. Slightly higher P helps newly planted trees, root crops, and bulbs establish.
- Potassium (K) — flower and fruit quality, plus stress resistance. High-potassium feeds (the famous "tomato food" formulas) drive fruit set and ripening.
A "balanced" fertiliser is roughly 1:1:1 ratio — 10-10-10, 7-7-7, 4-4-4. A "leaf" feed is high in nitrogen — 24-8-16, 20-5-10. A "tomato" feed is high in potassium — 4-3-8, 5-5-10. A "rooting" or "bloom" feed is higher in phosphorus — 5-10-5, 10-30-20.
Most plants get on fine with a balanced feed and a light second pass of the relevant high-nitrogen or high-potassium feed at the moment the plant needs it (leafy growth in spring, fruit-set in summer). The trick is not buying 12 specialised feeds — it's buying one balanced and one specialty for the crop you actually grow.
How we group the types
Four filters cover almost every fertiliser decision.
- Source. Organic (derived from plant, animal, or mineral sources — bone meal, fish emulsion, seaweed, chicken pellets) vs synthetic / inorganic (chemically formulated — ammonium nitrate, urea, potash, all the standard "Miracle-Gro" types).
- Form. Granular (top-dressed onto soil), liquid concentrate (diluted in a watering can), water-soluble powder (mixed with water), slow-release pellets (controlled-release coating dissolves over months), fertiliser sticks and tablets (slow-release for pots).
- NPK profile. Balanced, high-nitrogen, high-potassium, high-phosphorus, plus specialty trace-element feeds.
- Application. Top-dress (granular sprinkled around plants), drench (liquid into soil), foliar (liquid sprayed onto leaves), fertigation (mixed into irrigation water for greenhouse use).
1. Organic fertilisers
Derived from plant, animal, or mineral sources. Releases nutrients slowly as soil microbes break them down, feeds the soil-life ecosystem long-term, and is harder to over-apply.
Pros: Builds soil organic matter; feeds beneficial microbes; near-impossible to scorch plants; meets organic-certification standards (Soil Association in the UK, OMRI / USDA Organic in the US).
Cons: Slower to act (2 to 4 weeks for visible response); often smellier (fish, blood, chicken); typically lower NPK percentages so you apply more by volume.
Top US organic brands and NPK
- Espoma Plant-Tone — 5-3-3 balanced general purpose. The category leader in the US for organic granular feeds. Made from plant and animal-source nutrients; OMRI listed.
- Espoma Garden-Tone — 3-4-4 for vegetables and herbs. Slightly higher P and K for crop production.
- Espoma Tomato-Tone — 3-4-6 plus 8% calcium for blossom-end rot prevention. The tomato grower's organic choice.
- Espoma Bio-tone Starter Plus — 4-3-3 with mycorrhizae for transplanting. Good for new tree and shrub establishment.
- Dr. Earth Premium Gold All-Purpose — 4-4-4 probiotic-rich organic. OMRI listed, Non-GMO Project verified.
- Dr. Earth Home Grown Tomato, Vegetable & Herb Fertilizer — 4-6-3. The vegetable-garden go-to.
- Jobe's Organics All-Purpose Granular — 4-4-4 with biozome (microbe blend).
- Jobe's Organics Vegetable & Tomato — 2-5-3. Lower N, higher P, for fruiting crops.
- Miracle-Gro Organic Plant Food (concentrate) — 11-3-8 OMRI listed. Miracle-Gro's expansion into the organic segment; available in liquid for outdoor and indoor use.
Top UK organic brands and NPK
- Westland Organic Chicken Pellets — typically 4-2-1 or similar. The UK garden-centre standard organic granular, widely stocked at B&Q, Homebase, and independent garden centres.
- Vitax Organic Potato & Vegetable Fertiliser — 4-4-4 balanced organic. Listed in current RHS recommendations.
- Phostrogen Organic All Purpose Liquid Plant Food — organic liquid concentrate from the same brand that makes the classic Phostrogen (now owned by Bayer). Available at Amazon UK, Wilko, and most garden centres.
- Maxicrop Seaweed Extract — kelp-based liquid feed. Used as a tonic for stress and trace-element supply rather than primary NPK. Also sold as Maxicrop Tomato Growth Stimulant & Feed.
- Empathy RootGrow Mycorrhizal Fungi — not strictly a fertiliser but the RHS-endorsed mycorrhizal inoculant for transplanting trees and shrubs. Available at Wilko and major garden centres.
- Down to Earth (Carbon Gold) Biochar — soil amendment that boosts fertiliser efficiency over time.
2. Synthetic (inorganic) fertilisers
Chemically formulated, fast-acting, high-NPK concentrations. The dominant category in retail volume.
Pros: Fast plant response (visible within 1 to 2 weeks); precise NPK control; cheaper per nutrient unit; consistent results.
Cons: Easy to over-apply and scorch roots; some forms acidify or salinate soil over time; high-nitrogen forms can leach into watercourses; does not feed soil-life ecosystem.
Top US synthetic brands and NPK
- Miracle-Gro All Purpose Plant Food — 24-8-16 water-soluble powder. The category-defining US synthetic. Mix 1 tablespoon per gallon, drench every 7 to 14 days.
- Miracle-Gro Performance Organics — 11-3-8. The crossover line.
- Miracle-Gro Shake 'n Feed — slow-release granular at varied NPK depending on formulation (Tomato, Rose, Citrus, All Purpose).
- Osmocote Plus — 15-9-12 controlled-release pellets, feed for 6 months from one application. The greenhouse-and-container standard.
- MiracleGro Liquafeed Bottle Feeder — hose-end fertigation kit for outdoor lawns and beds.
Top UK synthetic brands and NPK
- Tomorite (Levington Tomorite Concentrated Tomato Food) — typically 4-3-8 liquid concentrate, the UK tomato-grower's near-default. Listed in current RHS recommendations. Available at every UK garden centre and supermarket.
- Westland Big Tom Super Tomato Food — competing UK tomato-food liquid concentrate. Sold at Wilko and most garden centres.
- Phostrogen All Purpose Plant Food — 14-10-27 water-soluble powder. The high-K British alternative to Miracle-Gro. Owned by Bayer Garden / Wilko since the brand changed hands. Widely stocked at Wilko and Amazon UK.
- Miracle-Gro All Purpose Plant Food (UK formulation) — 24-8-16, identical to the US product.
- Westland SafeLawn — child-and-pet-safe lawn fertiliser, ferrous-sulphate-free formulation. Available at B&Q, Homebase, and garden centres.
- Vitax Q4 — 5.3-7.5-10 plus trace elements. The traditional UK garden-centre all-purpose granular.
3. Slow-release and controlled-release fertilisers
A specialised form that suits container growing and busy gardeners. Polymer or sulphur-coated granules release nutrients gradually as soil moisture diffuses through the coating, typically over 3 to 6 months.
Pros: Apply once for a whole season; no risk of forgetting to feed; reduced leaching.
Cons: More expensive per nutrient unit; can over-deliver in hot summers (high temperatures speed release); harder to "course-correct" if the plant changes needs.
Top picks.
- Osmocote Plus — 15-9-12 controlled-release, 6 months. The greenhouse standard.
- Osmocote Smart-Release Plant Food — multiple formulations, US-marketed.
- Miracle-Gro Shake 'n Feed — 3-month slow-release granular.
- Levington Tomato Plant Food + Slow Release — UK slow-release tomato granular.
- Westland Gro-Sure 6 Month Slow Release Plant Food — UK controlled-release granular at varied NPK.
Slow-release is the smart choice for hanging baskets and large patio planters where weekly liquid feeding is impractical. Mix granules into the top inch of compost at planting and forget about feeding for 3 to 6 months.
4. Liquid fertilisers (concentrates and ready-to-use)
The fastest-acting form. Diluted into a watering can or hose-end feeder and applied as a soil drench or foliar spray. Nutrients absorb through roots within hours and through leaves within minutes.
Pros: Immediate response; precise dosing; flexible weekly schedule.
Cons: Wash out fast (especially in heavy rain or open-bed outdoor use); requires weekly or fortnightly application; more bottles to store.
Top picks.
- Tomorite (Levington) — 4-3-8 UK tomato liquid concentrate.
- Miracle-Gro All Purpose — 24-8-16 water-soluble powder.
- Phostrogen All Purpose Plant Food — 14-10-27 water-soluble powder.
- Maxicrop Seaweed Extract — UK kelp-based liquid tonic.
- Espoma Organic Indoor! — 2-2-2 liquid for houseplants. Pet-and-child-safe formulation.
Liquid feeds suit vegetables in containers, hanging baskets, indoor plants, and anywhere precise plant-by-plant feeding matters. For best-fertiliser-for-indoor-plants recommendations see our dedicated best fertiliser for indoor plants ranking.
5. Granular and pelleted fertilisers
Top-dressed onto the soil surface around plants and watered in. The traditional garden-bed feed.
Pros: Affordable per nutrient unit; easy to apply by hand; long-lasting (4 to 8 weeks per application).
Cons: Slower to act than liquids; needs to be watered in to start working; uneven distribution can scorch roots.
Top picks.
- Espoma Plant-Tone — US organic granular.
- Vitax Q4 — UK garden-centre balanced granular.
- Growmore (multiple UK brands) — 7-7-7 generic UK garden fertiliser, the long-standing British equivalent of US 10-10-10.
- Westland Organic Chicken Pellets — UK pelleted organic.
Top-dress in early spring as growth restarts and again in midsummer for hungry crops. Apply at the label rate — overapplication scorches roots.
6. Specialty and foliar feeds
The niche category — micronutrients, trace elements, biostimulants, foliar sprays for fruit set and disease tolerance.
- Epsom salts (magnesium sulphate) — corrects magnesium deficiency in tomatoes, peppers, and roses showing yellowing leaves with green veins. Dissolve 1 tablespoon per gallon, foliar spray.
- Iron chelate (sequestered iron) — for acid-loving plants (camellia, rhododendron, blueberry) showing chlorosis on alkaline soils.
- Calcium nitrate / Cal-Mag — for blossom-end rot prevention in tomatoes and peppers.
- Maxicrop Seaweed Extract — trace elements and biostimulants. UK favourite.
- Bone meal — 4-12-0 organic phosphorus and calcium. Plant under bulbs and bare-root trees.
- Blood meal — 13-0-0 fast organic nitrogen. Side-dress hungry leafy crops.
- Fish emulsion — 5-1-1 fast-acting liquid organic.
How to choose the right fertiliser
Match by crop and life-cycle stage.
- Lawns in spring → high-nitrogen granular. UK: Westland SafeLawn. US: Scotts Turf Builder.
- Leafy greens, lettuce, brassicas → balanced liquid every 2 weeks. Tomorite at half strength or Miracle-Gro at 1 tablespoon/gallon.
- Tomatoes, peppers, cucurbits at fruit set → high-potassium liquid weekly. Tomorite (UK), Espoma Tomato-Tone or Dr. Earth Tomato (US).
- Roses → specialist rose feed (high P and K). Tomato food works in a pinch — same NPK shape.
- Houseplants → balanced liquid at half strength fortnightly in spring and summer, none in winter. See best fertiliser for indoor plants.
- Trees and shrubs at planting → bone meal plus mycorrhizal fungi (Empathy RootGrow). Then balanced top-dress annually.
- Hanging baskets → slow-release pellets mixed into compost at planting, plus liquid weekly from week 6.
Match by gardening style.
- Hands-off → slow-release pellets, one application per season.
- Hands-on weekly routine → liquid concentrate, dilute and drench.
- Organic-only → Espoma, Dr. Earth, Westland Organic, Vitax Organic, Maxicrop.
- Maximum yield, less concerned about organics → Tomorite (UK), Miracle-Gro (US).
Common mistakes
Feeding plants in winter. Most houseplants and outdoor perennials are dormant or near-dormant from November to February. Feeding then either runs off (outdoors) or builds up as salt in pots (indoors). Stop feeding from October to March in temperate gardens.
Feeding stressed plants. A wilting houseplant or transplanted seedling needs water, not fertiliser. Feed only healthy actively growing plants.
Mixing organic and synthetic without thinking. Both work; mixing them is fine; just don't double-dose. If you used a slow-release pellet at potting, skip liquid feed for the first 6 weeks.
Ignoring the dilution rate. A "1 tablespoon per gallon" feed at 2 tablespoons per gallon will scorch roots. Read the label, measure, dilute. Half-strength weekly often beats full-strength fortnightly.
Treating fertiliser as a fix for unhealthy plants. Nine times out of ten, sad plants need correct watering, more light, or repotting — not more fertiliser. See our how to revive a plant guide before reaching for the bottle.
Try Growli: Open Growli and we recommend a feeding schedule for every plant in your photo library, with the specific UK or US brand match.
Related articles
- Best fertiliser for indoor plants — houseplant-specific picks
- What fertiliser for tomatoes — the tomato deep dive
- How to grow tomatoes — feeding within the full crop plan
- Types of soil — why soil texture changes how fertiliser behaves
- Types of vegetables — feeding the seven crop families
- Types of pots for plants — pot size and feeding frequency
- How to repot a plant — when to refresh vs feed
Reviewed and updated by the Growli editorial team. For questions about anything here, open Growli and ask — or email hello@getgrowli.app.
Frequently asked questions
What are the main types of fertiliser?
Four main types: organic (Espoma, Dr. Earth, Westland Organic — plant or animal sourced, slow-acting), synthetic / inorganic (Miracle-Gro, Phostrogen, Tomorite — chemically formulated, fast-acting), slow-release / controlled-release (Osmocote — coated granules releasing over 3 to 6 months), and liquid concentrates (Tomorite, Maxicrop — diluted in a watering can for weekly feeding).
What does NPK mean on fertiliser labels?
NPK = Nitrogen, Phosphorus (as P₂O₅), Potassium (as K₂O), expressed as percentages by weight. Nitrogen drives leaf and stem growth, phosphorus drives roots and flowers, potassium drives fruit and stress tolerance. A 10-10-10 product is 10% N, 10% P₂O₅, 10% K₂O. "Tomato food" formulas are high-K (e.g. 4-3-8); "lawn food" formulas are high-N (e.g. 24-8-16).
Is organic fertiliser better than synthetic?
Different strengths. Organic fertilisers build soil organic matter, feed soil microbes long-term, are nearly impossible to over-apply, and meet organic certification — but they release nutrients slowly. Synthetic fertilisers act fast and deliver precise NPK ratios but do not feed soil life and are easier to overdose. Most experienced gardeners use organic for long-term soil building plus synthetic liquid for in-season boosts.
What is the best fertiliser for tomatoes?
High-potassium liquid feeds. UK: Tomorite (Levington, ~4-3-8) or Westland Big Tom. US: Espoma Tomato-Tone (3-4-6) or Dr. Earth Home Grown Tomato (4-6-3). Apply weekly from the first flower truss through to last harvest. See our dedicated [what fertiliser for tomatoes](/blog/what-fertilizer-for-tomatoes) guide.
How often should I fertilise my plants?
Liquid feeds: weekly to fortnightly during the growing season (March to October in the UK, year-round in the US south). Granular feeds: once at the start of the season plus a midsummer top-up for hungry crops. Slow-release pellets: once per growing season. Stop all feeding in winter for most plants, with the exception of year-round growers in indoor heated environments.
Can you over-fertilise plants?
Yes, easily — especially with synthetic feeds. Symptoms include leaf-edge scorch (brown crispy margins), white salt crust on pot soil, sudden leaf drop, and stunted root growth. Flush pots with plain water several times to leach out excess salts. Skip the next 2 to 3 feeds before resuming at half strength. Organic feeds are much harder to overdose.
What's the difference between slow-release and liquid fertiliser?
Slow-release pellets release nutrients gradually over 3 to 6 months as soil moisture diffuses through their coating — apply once and forget. Liquid concentrates are mixed with water and applied every 1 to 2 weeks for instant uptake. Slow-release suits hanging baskets and large patio pots; liquid suits vegetables and indoor plants where precise weekly feeding pays off.
Are Tomorite and Miracle-Gro available in 2026?
Yes. Tomorite (Levington Tomorite Concentrated Tomato Food) remains widely stocked at UK garden centres and supermarkets and is listed in current RHS fertiliser recommendations. Miracle-Gro All Purpose Plant Food remains the dominant US synthetic feed and is also sold in UK retail. Westland, Phostrogen (Bayer), Vitax, Maxicrop, and Empathy are all current UK brands as of 2026.