WHAT’S WRONG WITH MY TOMATOES
By Virginia Ruschhaupt/Victoria County Master Gardener
May 31, 2025
Tomato cracking
Catfacing (Contributed photo)
Tomato rot
We have patiently waited.
We have worked and worked hard for our harvest. Tomatoes are developing, but things may still go astray. Our focus will be physiological tomato fruit problems, without fungal, bacterial, or viral origins. Most are preventable, but others are just victims of circumstance, such as the weather.
Blossom End Rot appears as a greenish-brown to black sunken or concave area at the blossom end of the tomato, with a dried out and leathery texture.
The primary cause is a lack of calcium in the fruit, but there are several possible reasons. It might indicate calcium deficiency in the soil or a calcium transport problem. Alternating dry and wet conditions, whether differences in rainfall or watering, can hinder the plant’s ability to absorb and transport calcium. Plants grown in containers that dry out are easily susceptible.
Calcium availability can be hindered by soil pH below 6.3 or higher than 7, or too much nitrogen or salt content. Plants with rapid growth and extensive leaf development may prioritize calcium uptake for the leaves, without much calcium left for the fruit. Plants damaged by herbicides or roots damaged by cultivating or fertilizing can impair calcium uptake from the soil.
Soil testing prior to planting can detect pH and nutrient deficiencies, so we can make adjustments. Supplementation to the soil, such as bone meal, crushed eggshells, or tomato- specific fertilizer can adjust calcium deficiency. Consistent watering, mulching and well-drained soil help maintain constant moisture.
There are a few resistant cultivars, but it is unlikely you will find them in our area.
The unaffected part of the fruit is edible if you pick it early. Removing all affected fruit on the vine decreases the whole plant’s susceptibility to fungi or bacterial secondary infections.
Tomato Cracking consists of vertical splits extending from top to bottom of the fruit or circular splits forming around the stem end of the fruit, sometimes a series of rings.
Cracks are caused by rapid changes in soil moisture, by irrigation or rain, causing the ripening flesh of the fruit to expand faster than the skin can grow. Extreme temperature change accompanying the moisture change exacerbates cracking. Prevention includes consistent watering, good drainage, and mulching.
High nitrogen and low potassium, additional contributors to cracking, can be alleviated by testing soil and correcting nutrient imbalance prior to planting. Potassium is important for healthy fruit development and strong skin.
Removing the affected fruits increases the opportunity for a continued healthy harvest, since the cracking creates open wounds susceptible to rot and pest infestations.
Catfacing includes malformed and puckered surfaces, dimples, crevices, or holes on the blossom end of the fruit, often occurring on the first fruits of the season. Tan-colored scar tissue may develop.
The most common cause is temperature below 50 deg. F during blossom development. Other contributing factors may be inconsistent moisture, high soil nitrogen, excessive pruning that stresses the plant, use of herbicides in the area, and thrips feeding on flower buds.
Control thrips by use of reflective mulches, natural predators, neem oil and insecticidal soap, as well as cleanliness and sanitation practices in the garden area.
Although flavor of affected tomatoes may be fine, remove them to avoid risk of fungal diseases. With warmer temperatures and control over some of the contributing factors, the remainder of the harvest may be normal.
Sunscald is pale, sunken, blistered areas on fruit exposed to excessive sunlight, often occurring when foliage coverage is poor. Use shade cloth during the hottest part of the day. Removing affected tomatoes reduces onset of pathogens.
Most of these physiological problems are preventable. Even upcoming fruit this season are likely to be fine if causes can be corrected.
Wishing you an abundant harvest of tasty tomatoes!
Gardeners’ Dirt articles appear in The Victoria Advocate each weekend.