Tomato fruits are in competition with each other, the leaves and stems for water and

To grow well, plants need a wide range of nutrients in various amounts, depending on the individual plant and its stage of growth. The three key plant nutrients usually derived from soil are nitrogen, phosphorus and potassium, while carbon, oxygen and hydrogen are absorbed from the air. Other vital soil nutrients include magnesium, calcium and sulphur. Gardeners can add nutrients by applying fertilisers (either artificial or naturally derived) to boost plant growth and improve flowering and fruiting.

These problems are usually seen on greenhouse-grown tomatoes, rather than those grown outdoors.

• Hard green areas on the ‘shoulder’ of the fruit: This is known as greenback. These areas remain hard and unpalatable as the rest of the fruit ripens. The causes are usually excess light, high temperatures, and/or insufficient feeding.
• Blotchy ripening and internal areas of white or yellowish tissue: Known as whitewall, the causes, as for greenback, are usually excess light, high temperatures, and/or insufficient feeding.
• Black sunken area at the bottom of the fruit: This is blossom end rot, see our advice on blossom end rot for further information.
• Splits and cracks in the fruit: See our advice on fruit splitting and cracking for further information on how and why this happens.

Tomatoes are particularly prone to what are known as physiological disorders: abnormal growth caused by non-infectious factors. This is partly due to the difficulty of controlling the sensitive requirements for temperature, nutrients and light.

Greenback and the internal white or yellowish discolouration (sometimes called ‘whitewall’) are problems caused by excess light and temperature and insufficient potassium fertiliser during fruit development and ripening. They are usually found on greenhouse rather than outdoor tomatoes.

Pale patches that fail to ripen can also be caused by variable water and nutrient levels.

To a large extent tomatoes can balance their nutrition and other physiological factors, but the practice of de-leafing can upset this balance and make tomatoes more prone to fruit ripening problems. De-leafing makes fruits easier to see and harvest and helps to reduce disease levels, but it should be kept to a minimum and be carried out no higher than the lowest truss of ripening fruits.

Non-chemical control

Control temperature and sunlight levels carefully to avoid extremes, using combinations of heating, ventilation, shade netting and white greenhouse paint as appropriate.

Choosing greenback-resistant cultivars will help avoid greenback and whitewall. Seed catalogues should list current greenback-resistant cultivars. Examples include ‘Alicante’, ‘Shirley’ and ‘Craigella’.

Avoid erratic watering and if plants with ripening fruit do become too dry, do not flood them, but bring the soil moisture level back up again gradually.

Feed tomatoes regularly to maintain high soil fertility. Special tomato fertilisers have high levels of potassium to encourage good fruit development. Adequate potassium nutrition is required to reduce greenback and whitewall, but excessive use of potassium-rich fertilisers can lead to magnesium deficiency and blossom end rot. Use of tomato feeds as directed by the manufacturer should avoid over or under supply of potassium.

Chemical control

Pesticides are not required to treat physiological problems as no pest or disease is involved. Therefore there is no chemical control.