Choosing nutrients for your plants

It's common to find that underfed plants are short of several nutrients all at once, so symptoms don't look like the pictures in books; the plants just look starved, stunted and sickly. Instead of trying to identify what's missing and how best to replace it, simply start each new growing season with an all-round dose of general-purpose feed, as it contains the 'big three' nutrients (nitrogen N, phosphorus P and potassium K) that plants need most of. That, plus a helping of well-rotted organic matter, gets most borders - and your edible crops - off to a flying start.

Nitrogen

Nitrogen promotes leaves, is fast acting and encourages lush green growth, but too much will inhibit flowering. Deficiency produces small, pale leaves and weak, spindly shoots.

Use nitrogen in spring (the start of the growing season) and regular summer top-ups for lawns and leafy veg. Apply as liquid feed or easily soluble powder/granules - for example, dried blood.

Phosphorus

Phosphorus assists the development of roots and tubers, but is also beneficial for general plant health. Deficiency is rare as phosphorus doesn't wash out of soil, even during very wet weather.

Use phosphorus at the end of the growing season to promote strong roots underground over winter. This will increase the root area, helping uptake of other nutrients and water.

Potassium

Potassium helps flowers and fruit to form, but is also crucial for toughening growth tor resisting pests and diseases. It also helps increase resistance to drought or extreme cold. Deficiency is more common on light, sandy soils. Signs include brown scorching and curling of leaf tips.

Apply potassium (also known as potash) little and often during the growing season, so plants can take it up when they need it.

Calcium

Calcium, usually in the form of lime, neutralises acid soils and makes micronutrients available that would otherwise be chemically 'locked up'. It's also essential for prevention of disorders such as blossom-end-rot (tomatoes) and bitter pit (apples).

Use calcium in early spring, if needed (do a soil pH test), but not at the same time as organic matter, with which it can react adversely.

Micronutrients

These vital nutrients, including iron and magnesium, are needed regularly in far smaller quantities, for plant health. Deficiency of certain nutrients can produce disorders in particular plants.

Use micronutrients in the growing season if a deficiency exists. Give magnesium to tomatoes using Epsom salts, or sulphate of iron to rhododendrons with yellowing leaves.

Trace elements

A wide range of minerals (selenium, molybdenum and even gold) are needed in minute quantities for optimal growth, reputed health benefits and flavour in fruit and vegetables.

Use trace elements at any time of the year. Mulches of home-made garden compost usually provide all that's needed. Some brands of organic fertiliser contain trace elements.