Why Tomatoes Split and How to Prevent Fruit Cracking

Illustration of tomato plants in pots with bamboo supports

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Tomato splitting and cracking is a physiological disorder caused by fluctuations in soil moisture and temperature. Unlike diseases or pest infestations, it is a reaction to growing conditions rather than an external biological agent. It typically manifests in late summer as the fruit swells and ripens, often resulting in superficial cracks, deep splits, or a rough, russeted skin surface.

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Diagnosing the cause of splitting and cracking

Identifying the specific type of skin damage can help determine whether the cause is related to water, temperature, or a combination of both. While these issues often overlap, the symptoms generally fall into three categories:

Cracking and splitting: These are typically the result of fluctuations in soil moisture. When a plant experiences a period of drought followed by a sudden surge of water (such as heavy rainfall or over-watering), the internal fruit tissue expands faster than the skin can stretch, causing it to rupture.
Russeting: This appears as a rough, corky skin surface and is primarily caused by variable temperatures during the growing process.
Catfacing: These are irregular concavities or corky scars on the fruit. This specific disorder occurs early in the season when temperatures fluctuate widely while the fruit is setting. It usually declines as nights become warmer in late summer.

The role of water and humidity

Water supply is the most common driver of fruit splitting. Tomatoes require a steady, consistent supply of moisture to swell and ripen. When the water supply is erratic, the plant undergoes ‘stop and start’ growth, which stresses the fruit skin.

The risk is significantly higher for plants grown in containers, pots, or growing bags because these mediums dry out more rapidly than open ground. In contrast, plants grown in border soil typically develop more extensive root systems, which provide a natural buffer against moisture fluctuations. Outdoors, heavy rain can lead to flooding, which often triggers splitting; in these instances, there is no immediate remedy other than harvesting the fruit promptly to reduce losses.

Atmospheric humidity also plays a role. As autumn approaches, increasing humidity can slow transpiration, affecting how roots absorb water. Furthermore, existing splits and cracks create entry points for fungal moulds, such as grey mould (Botrytis cinerea), which can then infect the fruit.

Reducing splitting in greenhouses and conservatories

Gardeners have more control over the environment in a greenhouse than outdoors. To reduce the risk of physiological disorders, the goal is to avoid extremes in temperature and light.

Temperature monitoring: Use a maximum-minimum temperature thermometer to track fluctuations. This allows you to identify if the greenhouse is becoming too hot during the day or too cold at night.
Ventilation: Ensure adequate airflow to prevent overheating. If a greenhouse has poor built-in ventilation, consider approved ventilation improvements; glazing alterations should follow the greenhouse maker’s guidance. For polythene tunnels, installing wind-up sides or adding extra shading is recommended.
Light management: Use white greenhouse paint or shade netting to prevent excessive sunlight from causing temperature spikes.

Practical watering and feeding strategies

Maintaining a constant level of soil moisture is the most effective way to prevent splitting. Avoid the cycle of letting the soil dry out completely and then flooding it.

Watering techniques: To ensure water reaches the roots without saturating the stem (which can cause rotting), you can use a focused irrigation method. For example, if you sink a 15cm pot into the ground alongside your tomato plants and water directly into that pot, the moisture is delivered deep into the root zone rather than sitting around the neck of the plant.

Feeding for fruit development: Maintain suitable nutrition without overfeeding; additional fertiliser is not a cure for split fruit. Use fertilisers specifically formulated for tomatoes, as these contain high levels of potassium, which is essential for proper fruit development. Regular feeding helps maintain the plant’s overall resilience to environmental stress.

Managing outdoor tomato plants

Managing temperature for outdoor tomatoes is nearly impossible, meaning the focus must remain on moisture and harvesting. Because outdoor plants are subject to the unpredictability of rainfall, the following steps can help:

Mulching: Apply a thick layer of garden compost or well-rotted manure around the base of the plants, leaving a small gap around the stem to prevent rot. This mulch helps retain soil moisture and reduces the impact of dry spells.
Supplemental watering: During dry periods, water regularly to keep moisture levels as constant as possible.
Strategic harvesting: As the season ends, ripening slows due to shorter days and cooler nights. To avoid the increased risk of splitting during this period, pick fruits when they are nearly ripe and allow them to finish ripening indoors in a warm, dark place.

Useful products for this job

The links below open Amazon UK product searches. Check the exact item, seller, current price and compatibility before buying.

Maximum-minimum temperature thermometer: Essential for monitoring temperature fluctuations in greenhouses to prevent russeting and catfacing. Ensure it has a clear display for reading the highest and lowest temperatures reached over a 24-hour period. Search Amazon for Maximum-minimum temperature thermometer.
High potassium tomato fertiliser: Supports normal fruit development when used at the labelled rate; it cannot repair splitting. Check the NPK ratio to ensure potassium (K) is the dominant nutrient for the fruiting stage. Search Amazon for High potassium tomato fertiliser.
White greenhouse paint: Used to control sunlight levels and prevent extreme temperature spikes in greenhouses. Verify the paint is specifically designed for greenhouse glass or polycarbonate to ensure it can be removed later. Search Amazon for White greenhouse paint.

Related garden guides

Sources and further guidance

Guidance researched in September 2026. The feature image is an AI-generated illustration. Product guidance is based on published information, not hands-on testing.