Although easy to grow, tomato fruits can suffer from splitting and cracking in late summer. This is difficult to prevent, as it is caused by fluctuating temperatures and water supply - which are often out of the control of the gardener.
What is the problem?
This is an example of a physiological disorder – a problem caused by the growing conditions rather than by a pest or disease agent. Inappropriate levels of water, light, temperature and nutrients can all cause a variety of physiological disorders in tomatoes. The fruits are especially vulnerable as they are at the growing tips and have to compete with the new shoots for water and nutrients.
Symptoms and causes
- Split, cracked or heavily russeted fruit: This is usually caused by variable water supply and/or fluctuating temperatures.
- Corky scars and irregular concavities in the fruit, known as ‘catfacing’: This is usually caused by variable temperatures.
- The ‘catfacing’ symptom is due to temperatures fluctuating too widely early in the season as the fruit is setting. It tends to occur early in summer, declining as the nights become warmer in late summer.
- Russeting (a rough skin surface) and superficial marks are caused by variable temperatures, whereas cracking and splitting are due to fluctuations in soil moisture.
- Water supply can be especially variable in growing bags and pots, and this requires regular monitoring both in the greenhouse and outside. Outdoors, variations in rainfall may cause damage. Although watering in dry spells will help, in periods of heavy rain there is no remedy for the damaging effects of flooding, which often leads to fruit splitting and cracking. Prompt harvesting of fruits may reduce losses.
- ‘Stop and start’ growing caused by insufficient warmth and fluctuating temperatures or moisture levels can harm the fruits.
- Tomato fruits need warmth and moisture to swell and ripen. At the end of the growing season ripening will slow down and fruits are best picked and ripened indoors in a warm dark place. At this time of year the nights are cool and day length is short with the sun lower in the sky. It is difficult to avoid conditions that lead to uneven ripening and fruit splitting or cracking.
- The increasing humidity as autumn approaches may also promote fungal moulds, especially grey mould (Botrytis cinerea). Splits and cracks will allow such fungi to enter and infect the tomato fruits.
- In the greenhouse or conservatory, control temperature and sunlight levels carefully to avoid extremes, using combinations of heating, ventilation and white greenhouse paint as appropriate. A good maximum-minimum temperature thermometer is essential. Poor quality greenhouses often lack adequate ventilation arrangements and temporary removal of glass panes during summer can help remedy this lack. Polythene tunnels have few options for decreasing the temperature except using extra shading or installing wind-up sides to increase ventilation.
- Managing temperature is almost impossible for tomatoes grown outdoors.
- Feed regularly to maintain high soil fertility. Special tomato fertilisers have high levels of potassium to encourage good fruit development.
- Water to maintain a constant level of soil moisture. This is especially important when growing in growing bags, pots or other containers. Outdoors, water to maintain as constant a level of soil moisture as possible. Plants grown in border soil, indoors or out, usually have a more extensive root system which helps protect them from fluctuations in water supply.
As fruit splitting and cracking is a physiological rather than a pest or disease problem, there is no point in using pesticides to treat the problem. There are no chemical controls.
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