Garden Plants

60-second guide: sick plants

By Julie Hollobone

Know how to react when your plants look less healthy than they should

Interveinal chlorosis is clearly visible on this skimmia

'A deficiency in nitrogen usually appears as a yellowing of leaves due to insufficient chlorophyll being manufactured by the plant to supply all the leaves.'

The symptoms of a nutrient shortage are related to the role of the nutrient in normal circumstances. Just how a deficiency is indicated can vary between different types of plants and how they are grown, so some can be difficult to detect.

Nitrogen deficiency

A deficiency in nitrogen usually appears as a yellowing of leaves due to insufficient chlorophyll being manufactured by the plant to supply all the leaves. This effect is described as chlorosis. Usually, the older leaves are sacrificed for the newer growth, so they look yellow then die while the plant continues to produce new leaves. Overall, however, the foliage cover will get thinner and growth less vigorous.

Phosphorus deficiency

A lack of phosphorus can result in poor root growth, so the plant is less able to take to take up sufficient supplies of water and other nutrients. The plant will tend to grow slowly and foliage may have a blue tint.

Potassium deficiency

A potassium deficiency will result in less flower production which may lead to a lack of fruit. Sometimes, the shortage shows up in the leaves as brown edges. Other symptoms may be a combination of several deficiencies.

Magnesium, iron or manganese deficiency

A shortage of these nutrients can occur on very acid or alkaline soils and shows up as a yellowing of the leaves, mainly in the areas between the veins known as the interveinal chlorosis. Sometimes, older leaves are affected more than younger ones, depending on which nutrient is deficient.

How to respond

A nutrient deficiency needs to be treated fairly quickly, as if it is ignored plant growth is likely to be weak and then becomes more vulnerable to attack by pests or diseases. In this instance, organic matter is not appropriate, but a fertiliser will give a fast response, especially if it dissolves quickly into the soil water.

If you know a plant is deficient in one nutrient, you can apply a straight fertiliser, but when you’re not sure, or if there are several deficiencies, you should do what most gardeners do and use general-purpose fertiliser. If applied as a liquid on to soil, as well as to the foliage, the response to feeding may be more rapid.

This article is extracted from Gardens Monthly magazine's How to Garden series and adapted by Sarah Brocklehurst.

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