8 Causes of Irregular and Deformed Tomatoes

There’s nothing quite like anticipating your first ripe tomato of the season, only to discover it’s grown into an unrecognizable, almost alien-like shape. Catfacing, zippering, cracking, and other deformities can turn fruits into disappointments that barely resemble tomatoes at all.

While irregular tomatoes are usually safe to eat, they often indicate underlying problems with your plants’ growing conditions. Understanding what causes these deformities puts you in a better position to prevent them from happening repeatedly in your garden.

Many of the factors that cause irregular fruit development are within your control, though some environmental influences will always be unpredictable. Here are the primary culprits behind those strange-looking, irregular, and deformed tomatoes and what you can do to minimize their occurrence.

Temperature Extremes

Temperature fluctuations during the critical flowering and early fruit development period are responsible for many tomato deformities. When temperatures swing dramatically during pollination, fruits often develop irregular shapes and sizes.

Cool nights below 55°F (13°C) during flowering can cause catfacing, where fruits develop deep creases and puckered surfaces in a radial pattern. The cold interferes with normal flower development, resulting in irregular, deformed tomatoes.

Hot days above 90°F (32°C) create different problems. Excessive heat causes poor pollination and can lead to pointed, elongated fruits or hollow gaps within otherwise normal-looking tomatoes.

Large-fruited varieties are particularly susceptible to temperature-related deformities. Cherry tomatoes like ‘Sun Gold’ and smaller varieties often handle temperature swings better than larger types.

Poor Pollination

Inadequate pollination is behind many of the most bizarre tomato shapes you’ll encounter. When flowers aren’t properly pollinated, fruits develop unevenly with missing sections or unusual bulges.

Tomatoes are self-pollinating, but they still need some movement to transfer pollen within the flower. Lack of wind or beneficial insects can result in incomplete pollination, especially in greenhouses or protected growing areas.

Hand-pollinating with a small brush or gently shaking flowering plants can improve fruit set and reduce deformities. This is particularly important for indoor-grown plants or times when natural pollination is limited.

High humidity above 70% can cause pollen to clump together, making it less effective for pollination. Improve air circulation around plants to reduce humidity levels and encourage better pollen transfer. Otherwise, whip out your paintbrush and pollinate yourself to prevent irregular, deformed tomatoes.

Genetics

Some varieties are naturally prone to producing irregular, deformed tomatoes due to their genetic makeup. Heirloom varieties (while flavorful) often carry genes that predispose them to fruit deformities.

Beefsteak tomatoes are notorious for developing catfacing and other irregular shapes. This tendency is bred into many large-fruited varieties as a trade-off for size. If a consistent shape is important to you, choose smaller-fruited varieties or modern hybrids selected for uniform fruit development.

Certain varieties like ‘Brandywine’ and ‘Cherokee Purple’ are known for producing ribbed, irregularly shaped fruits. This is normal for these varieties and not necessarily a sign of poor growing conditions.

Understanding your variety’s typical fruit characteristics helps you distinguish between normal variation and actual problems. Research varieties before planting if uniform fruit shape is a priority for your garden.

Inconsistent Watering

Irregular moisture levels during fruit development cause several types of tomato deformities, particularly cracking and splitting. Plants that experience drought stress followed by abundant water often produce fruits with growth rings or cracks.

Cracking occurs when fruits expand rapidly after a period of water stress. The skin can’t keep up with the rapid cell expansion, resulting in splits from the stem end. This typically happens late in the season when large fruits are nearly mature.

Maintain consistent soil moisture throughout the growing season to prevent water-related irregular or deformed tomatoes. Deep, less frequent watering encourages better root development and helps buffer against moisture fluctuations.

Nutrient Imbalances

Both deficiencies and excesses of certain nutrients can cause tomato fruits to develop abnormally. Calcium deficiency is particularly problematic for fruit development and shape, usually caused by inconsistent watering rather than a lack of calcium in the soil.

Potassium deficiency often results in fruits with poor color development and irregular ripening patterns. Fruits may develop yellow shoulders or ripen unevenly, creating a mottled appearance that affects both color and texture.

Excessive nitrogen during fruit development can cause hollow fruits or unusual internal structures. Plants with too much nitrogen continue vegetative growth at the expense of proper fruit development, resulting in tomatoes that look normal externally but are irregular and deformed inside.

Boron deficiency affects cell wall development and can cause fruits to develop thick areas or unusual textures. This micronutrient is essential for proper fruit formation, though deficiencies are relatively uncommon in most soils.

Physical Damage

Damage to developing fruits often results in permanent tomato deformities as the fruit continues to grow around the injured area. This can be caused by pest damage, the weather, or gardeners themselves.

Small insects can cause scarring on young fruits that results in raised, corky areas as the fruit matures. These scars become more pronounced as fruits expand, creating permanent blemishes or unusual textures.

Hail damage creates distinctive scarring patterns on fruits. Even minor hail can cause significant deformities in developing fruits. Luckily, mature fruits are more resistant to damage.

Rubbing against stakes, cages, or other support structures can cause flat spots or unusual indentations in growing fruits. Check support systems regularly to ensure they’re not causing damage to developing fruit clusters.

Overcrowding

When fruit clusters are too dense, individual fruits can’t develop properly due to competition for space and nutrients. This crowding often results in irregular and deformed tomatoes.

Large clusters may need thinning to allow remaining fruits to develop to full size and proper shape. Remove smaller fruits early in development to give the remaining ones more space and resources.

Inadequate pruning can contribute to overcrowding by allowing too many fruit clusters to develop simultaneously. Plants with limited energy spread thin across many fruits often produce smaller, less uniform results.

Support structures that constrain plant growth can also contribute to fruit crowding. Make sure plants have adequate space to spread and that support systems don’t force fruit clusters into cramped positions.

Late-Season Stress

Environmental stress late in the growing season can cause fruits to develop unusual characteristics even if early development was normal. Plants struggling with disease, pest pressure, or extreme weather often produce irregular, deformed tomatoes.

Determinate varieties are particularly susceptible to late-season deformities as they channel all their energy into final fruit development. Any stress during this critical period can result in unusual fruit shapes or sizes.