Organic vs Synthetic Fertilisers
Choosing fertiliser is easier when you start with your soil and plants rather than a product label. Organic materials feed soil life as well as crops, while synthetic fertilisers give quicker, measured nutrition. Both can have a place, but careful timing, modest use and regular compost matter most in a productive British garden.
Begin by assessing what needs feeding. Observe pale leaves, slow growth, poor flowering or light, hungry soil, but remember that cold weather, drought and waterlogging can cause similar symptoms. Improve the basics first: add garden compost, keep soil covered and water evenly. Organic fertilisers include well-rotted manure, composted green waste and plant-based feeds. They release nutrients gradually as soil organisms work, so they suit beds, borders and long-season vegetables. Synthetic fertilisers are manufactured mineral nutrients that plants can take up rapidly. They can help a crop that needs a prompt boost, particularly in containers, but they do not replace organic matter or sound soil care. Avoid applying either type simply because the calendar says so.
Use organic fertilisers when building a bed or preparing an allotment plot. In late winter or early spring, spread a 3 to 5 cm layer of garden compost or well-rotted manure over bare soil, keeping it away from woody stems. Let worms and weather draw it in rather than digging deeply. This improves crumb structure, moisture holding and drainage as well as supplying nutrients. On very fertile ground, use less, especially before root crops, which can make excessive leafy growth at the expense of roots. Organic feeding is not instantly predictable because release depends on warmth and moisture. That is usually helpful for steady growth, but it means planning ahead is important for demanding crops such as brassicas and potatoes.
Choose a synthetic fertiliser only when you need a known nutrient balance or a quick response, and use it sparingly. Follow the manufacturer's label exactly, because strength and application rates vary widely. Scatter granules evenly on moist soil, then water them in if the label permits; do not leave them on foliage. For pots, a diluted liquid feed applied to already-moist compost is usually easier to control than adding extra granules. Never assume more feed means more fruit or flowers. Overfeeding can scorch roots, encourage soft growth and wash nutrients away in heavy rain. Store fertilisers dry, labelled and out of reach of children and pets, and sweep up spills rather than hosing them into drains.
Match feeding to the crop's stage. Leafy brassicas, leeks and sweetcorn benefit from fertile soil before planting and occasional support while actively growing. Fruiting crops such as tomatoes, courgettes and peppers need steady watering and feeding once flowers and fruit are forming, particularly in containers. Potatoes and roots are best grown in soil that was enriched for the previous crop, not freshly loaded with manure. Feed established shrubs and perennials only if growth is weak or the soil is poor; a spring compost mulch is often enough. Stop routine feeding late in the season, when plants should slow naturally. Healthy soil and appropriate spacing prevent many apparent fertiliser problems.
Containers need closer attention because nutrients are washed out each time you water. Start with fresh peat-free multipurpose compost, add drainage holes and choose a pot large enough for the crop. As roots fill the container, begin a regular, light feeding routine appropriate to edible or ornamental plants, following the label. Check moisture before every feed, as dry compost and concentrated feed are a poor combination. Organic liquid feeds can be useful here, but they still need accurate dilution. Refresh containers annually rather than repeatedly adding more fertiliser to exhausted compost. Tip old compost onto the compost heap or use it as a mulch where suitable, then replenish pots with new peat-free compost and some garden compost.
Keep a simple notebook for each bed and container. Record what you added, when you applied it, weather conditions and how plants responded. This prevents duplicate feeding and helps you notice whether compost, watering or a change of position solved the issue. Test soil if recurring problems persist, especially on a new allotment or where plants repeatedly fail. Aim for a balanced approach: compost and mulches for long-term fertility, careful organic feeds where needed, and synthetic fertiliser only as a measured tool. Do not feed stressed plants during drought, frost or waterlogging. Water first, wait for recovery, then decide whether nutrition is genuinely the limiting factor.
Frequently asked questions
Is organic fertiliser always better for the garden?
Not always. Organic fertiliser is excellent for improving soil structure and supporting steady growth, but nutrient release is slower and variable. A carefully used synthetic fertiliser can correct a clear short-term need, especially in containers. Most gardens do best with regular compost, sensible watering and only enough additional feed for the crop.
Can I use garden compost instead of fertiliser?
Garden compost is the foundation for many beds because it adds organic matter and some nutrients. It may not provide enough immediately available nutrition for very hungry crops in poor soil or long-term containers. Use compost routinely, then add a suitable fertiliser only where plant growth and the crop's needs justify it.
When should I avoid fertilising?
Avoid feeding plants that are drought-stressed, frozen, newly wilted after transplanting or sitting in waterlogged ground. Do not apply fertiliser before heavy rain, as nutrients may wash away. Late-season feeding can also encourage tender growth. Restore suitable moisture and growing conditions first, then feed only if needed.
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 19 Sep 2026.