Compost vs Fertiliser: What Is the Difference?
Compost and fertiliser both support plant growth, but they do different jobs. Compost improves the soil's structure, moisture balance and living community over time, while fertiliser supplies concentrated plant nutrients more directly. Most gardens benefit from using compost as the foundation and fertiliser only where crops show an extra need.
Think of garden compost as a soil improver first. It is made from decomposed garden and kitchen materials, and it feeds soil organisms while helping soil hold water and air. Spread it on beds, borders and around established plants to improve the growing environment gradually. Fertiliser, by contrast, is designed to provide nutrients that plants can take up more readily. It may be organic or mineral-based, but always follow its label directions and use only what the crop needs. Compost is not identical in every batch, because the ingredients and maturity vary. Fertiliser is more predictable for targeted feeding, but it cannot by itself create the crumbly, moisture-retentive soil that regular organic matter builds.
Begin each season by assessing your soil and crops. Vegetables that demand plenty of nutrients, such as brassicas, sweetcorn and courgettes, need fertile ground, while herbs and many established shrubs need less. If a bed has been mulched and composted regularly, plants may need little extra feeding. Pale leaves, weak growth or poor yields can have many causes, including cold weather, dry roots, waterlogging, pests or compaction, so do not assume fertiliser is always the answer. A soil test can help identify broad nutrient and acidity patterns. For a clearer recommendation, take a sample to the RHS or a local garden centre. Use results alongside observations of drainage, sunlight and crop rotation.
Apply mature garden compost in autumn or spring. Spread a 5 cm layer over bare vegetable beds and lightly fork it into the surface, or leave it as mulch for worms to draw down. Around fruit bushes, perennials and roses, lay compost over the root area while keeping it clear of stems. Use only fully decomposed material that smells earthy and has no recognisable fresh scraps. Fresh compost can temporarily tie up nutrients or attract unwanted visitors. In containers, use peat-free multipurpose compost as the main growing medium, refreshing pots with a surface layer of mature compost where appropriate. Compost helps sandy soils retain water and can improve the workability of heavier soils over repeated seasons.
Use fertiliser as a supplementary tool, not a substitute for soil care. Choose a product suited to the crop and apply it at the time stated on its label, usually when plants are actively growing rather than dormant. Water the soil beforehand if it is very dry, then apply carefully to the root area and water in if the instructions advise it. Keep fertiliser off leaves, stems and hard surfaces. Avoid feeding newly stressed, wilted or waterlogged plants until the underlying problem is corrected. On an allotment, keep a note of what was fed and where, so you do not repeat applications unnecessarily. Excess nutrients can wash through soil, especially in wet weather or on sandy ground.
Match the approach to each place in the garden. A newly cleared vegetable plot usually benefits most from compost and steady improvement before any targeted feeding. Pot-grown tomatoes, cucumbers and flowering containers may need additional fertiliser because roots are confined and regular watering leaches nutrients from compost. Leafy crops can respond to fertile soil, but avoid chasing soft growth with excessive feeding. Legumes such as broad beans, French beans and peas generally need less added fertiliser than hungry fruiting crops when soil is reasonably fertile. Mulch fruit trees and shrubs with compost each year, then only add fertiliser if growth, soil assessment or specialist advice indicates it is useful. Good watering and spacing remain just as important.
Store compost and fertiliser sensibly. Keep mature compost covered enough to prevent nutrients washing away, while allowing air to circulate in a compost heap or bin. Store fertiliser in its original closed container, dry and out of reach of children and animals. Wash hands after handling either material and clean tools before moving to another bed. At the end of the season, review what worked: did mulch reduce watering, did crops grow evenly, and were any beds persistently weak? Increase compost-making from grass clippings, prunings and kitchen vegetable waste, then reserve purchased fertiliser for genuine gaps. This combined approach is economical, adaptable and kinder to the long-term condition of your garden soil.
Frequently asked questions
Is compost enough to grow vegetables?
Often, regular applications of mature compost provide an excellent base for vegetables, especially on reasonably fertile soil. Hungry crops in containers or repeatedly cropped beds may need supplementary fertiliser, but this varies with soil, weather and watering. Watch plant growth, rotate crops and improve organic matter annually before deciding that extra feeding is necessary.
Can I use compost and fertiliser together?
Yes. Use compost to improve the bed or border and retain moisture, then add fertiliser only where a particular crop needs it. Compost does not make fertiliser harmful or unnecessary; they have separate roles. Apply fertiliser according to its label and avoid adding more simply because compost is also present in the soil.
Why are my plants struggling after adding fertiliser?
Fertiliser cannot correct shade, poor drainage, root damage, drought or cold weather. Too much can also stress plants, particularly in pots or dry soil. Pause further applications, check soil moisture and roots, and review the product directions. Improve the soil with compost over time, but address the actual growing condition causing the problem.
General guidance for UK home gardens and allotments. Conditions vary by region, soil and season; the RHS or a local garden centre can give site-specific advice. Page updated 18 Sep 2026.