Chlorosis is usually a sign that a vital nutrient is lacking, although viruses may be to blame. If a deficiency is the cause, correct feeding makes all the difference.
Deciduous trees lose their leaves every autumn and evergreen trees shed some of their leaves in the summer. However, when leaves change colour from green through yellow to brown and fall at other times of the year, there is cause for concern.
Make regular checks so that problems can be treated early on. Once the whole plant is affected and growth stunted, it is more difficult to treat.
Feeding plants
There is often a distinctive pattern to the chlorosis which gives a clue to the cause. If you are uncertain, feed the plants with a balanced fertilizer containing the whole range of essential nutrients.
A foliar feed (one applied to the leaves) acts more quickly than one applied to the soil. Apply a liquid feed directly to the leaves on a dull day, using a spray or a watering-can with a rose nozzle.
If chlorosis persists, look for another cause. Waterlogging may be the culprit if a whole plant suddenly turns yellow. Bleached leaves may be the result of a plant that needs plenty of sun not getting enough light.
Nitrogen
Chlorosis in lawns and leafy vegetables is often due to a lack of nitrogen.
• Apply a fertilizer during the growing season.
• For a quick response use a dried-blood or a liquid fertilizer with nitrogen.
• At the beginning of the season, apply a slowrelease fertilizer which becomes available to the plants over a long period.
• Hoof-and-horn meal is a traditional slow-release nitrogen fertilizer, but other types are available.
Iron
Acid-loving plants, such as rhododendrons and skimmias, can only use iron if the soil they are grown in is acidic. Planted in an alkaline soil, the whole plant can eventually look very sickly as a result of its failure to take up iron.
In gardens with alkaline soil, apply a fertilizer containing sequestered or chelated iron around these plants annually in spring.
IMPORTANT
Do not put plants infected with a virus on the compost heap. Healthy plants could be infected with the resulting compost. To prevent spread from garden tools, clean them with a garden disinfectant.
Magnesium
Magnesium often washes out of soils, and apple, tomato, potato and annuals are vulnerable at the end of a wet growing season. Watch out for a premature yellowing of the leaves. Magnesium is also difficult for plants to take up if too much potassium has been applied to the soil, and chlorosis may result.
• For a quick cure, spray leaves with a solution consisting of 6g of magnesium sulphate (Epsom salts) to 1 litre water.
• For a slower action, spread dolomitic (magnesian) limestone on the soil at the rate of 240g per square metre.
Acid soils
Acid soils may prevent plants from taking up the nutrient molybdenum. Cauliflowers and broccoli are the plants most likely to show chlorosis as a result, although annuals may suffer from a lack of this essential trace element.
• Water affected seedlings with a liquid feed containing molybdenum.
• Before growing another crop, add lime to the soil to make it less acidic.
• Continue to look out for symptoms and apply a feed whenever necessary.
Manganese
Lack of manganese is most common on poorly drained, alkaline soil and is often the cause of chlorosis on vegetable and fruit crops. Spray a foliar feed containing manganese on to the leaves for a quick response, and try to improve soil drainage.
TIP - SOIL CHECK
Check soil with a pHtesting kit to find (Rut if it is acidic, neutral or alkaline. Identifying the soil type gives a good sign of which nutrients are likely to be unavailable. As a precaution, feed susceptible plants with a fertilizer containing all necessary nutrients. Do not wait until plants show signs of chlorosis. Ensure they stay healthy from the moment they are planted.
Leafy plants such as tomato use a lot of nutrients. Prevent chlorosis by giving the correct feed from the beginning.
Chlorosis varies in appearance, depending on its cause. A nutrient deficiency usually affects a few leaves at first.