7 Mistakes That Are Causing Your Tomatoes to Rot Before They Ripen

For vegetable gardeners, few things compare to biting into the first tomato of summer. But sometimes these fruits, which can be finicky to grow, rot before you have the opportunity to enjoy them. This may happen for a number of reasons, from unwanted pests and diseases to inadequate care. To ensure your fruits stay healthy until harvest, we spoke to gardening experts who shared the most common reasons tomatoes rot before they ripen, and what to do if this is happening to your crops. 

Overcrowding Plants

Tomatoes need airflow to remain healthy and prolific. But it's easy to forget when planting tiny seedlings in spring how large your tomato plants will get by late summer. Be sure to space your plants adequately when planting so they have room to breathe when they reach maturity. If you don't, you might restrict airflow, leading to diseases that can cause the fruit to rot before it ripens. 

Blossom-End Rot

One of the most common issues you may encounter when growing tomatoes is blossom-end rot, caused by low calcium levels in the fruit. Blossom-end rot presents as brown or black decay on the end of tomato fruits where the blossom was. "Blossom-end rot is a frustrating disorder that can be a common occurrence on tomatoes, but it can also happen to peppers, eggplants, cucumbers, melons, and summer and winter squash," says gardening author Susan Mulvihill. 

Regular watering is the best way to prevent blossom-end rot from occurring because this helps the roots obtain calcium. Mulvihill also says to avoid disturbing tomato roots when weeding, which makes it harder for them to do their job. "This disorder is usually more prevalent earlier in the season when young plants have smaller root systems," she says. As the plants grow, gardeners will encounter fewer instances of blossom-end rot.

Over-Fertilizing

Too much of a good thing can be harmful. It's common for gardeners to over-fertilize their tomato beds with nitrogen. Tomatoes are sensitive to nitrogen, and too much of it can cause wilted, yellowing leaves and prematurely rotted fruit. Before using nitrogen as an additive, consider conducting a soil test to ensure your soil needs this nutrient. You may find you're better off leaving the plants to themselves. 

Inconsistent Watering

Tomatoes are susceptible to splitting, which can lead to rotting. Tomatoes usually split when given a sudden influx of water, which could happen if you go too long between watering sessions and try to make up for it, or if there is a sudden, heavy rainstorm. "Ordinarily, tomatoes can handle rain, but a heavy drenching causes the flesh of ripening tomatoes to expand. Unfortunately, the skin isn’t able to stretch along with it, which makes them split open," says Mulvihill. 

Consistency is key to minimizing splitting. Water your tomatoes deeply, frequently, and consistently so water intake stays the same daily. "When it comes to watering, the goal should be to keep the soil lightly moist rather than going from bone-dry conditions to absolutely drenching the plants and soil with water," says Mulvihill. She also recommends harvesting nearly-ripe tomatoes before a rainstorm. 

Lack of Crop Rotation

Even small-scale gardeners need to practice crop rotation, especially with tomatoes. "There are many soil-borne fungal diseases. Crop rotation goes a long way toward keeping these under control, which means less troubleshooting for the summer gardener," says master gardener Charlotte Germane. She explains that the basic concept is to avoid planting the same vegetable in the same location for three years. "At the end of the summer, look around the garden, make a simple map, and choose a different spot to plant tomatoes next year. For gardeners with little room, she suggests growing tomatoes in containers, where it's easy to refresh the soil each growing season. 

Too Much Sun

Tomato plants require full sun for optimum growth, but the fruits do best when slightly shaded. "A healthy tomato plant has plenty of leaves that also shade the growing fruits," says Germane. "If the leaves are attacked by pests or diseases and wither, the young tomato fruits can get too much sun exposure and develop big blistery white or tan patches, called sunscald." She recommends discarding any damaged leaves and fruits. To prevent sunscald, Mulvihill warns against pruning your tomatoes for shape and recommends covering the plants with shade cloth. 

Exposure to Fungal Disease

Fungal diseases like early blight can also cause rotten fruit. "Early blight shows up near the start of the growing season," says Germane. "The dark 1-inch spots on the lower leaves are caused by a fungus that lives in the soil." To solve the problem, she suggests cutting off and discarding the diseased leaves and fruit, then cleaning your pruners with rubbing alcohol to keep from infecting other plants. "Spray the tomato plants with an organic fungicide, like copper spray, and don't do any overhead watering," she says.