Tomatoes are among the finer things we look forward to in summer. Fresh tomatoes from the garden are a real treat, so it’s disappointing to see a tomato in mid-growth with a bruised-looking splotch on the blossom part of the fruit. Blossom end rot in tomatoes (BER) is a common problem for gardeners. Its cause lies in a plant’s inability to absorb enough calcium to reach the fruit. Other vegetables like bell peppers, eggplant, and squash can be subject to blossom rot as well.
Blossom end rot can be a signal that there may not be enough available calcium in the soil. Even if the soil has sufficient calcium, the tomatoes may have been subjected to conditions which block their ability to uptake it. Fortunately, preventing tomato blossom end rot is possible.
Tomato Plants with Blossom End Rot
When a tomato plant is flowering well, tiny fruits begin to form. The leaves may be healthy, plentiful, and verdant. On the outside, it can appear the plant is vigorous and a bountiful harvest is expected. But during formation of the fruit, small imperfections can begin to show up. Blossom end rot in tomato plants starts small but can end up ruining the fruit. There are both internal and external tomato blossom end rots. In the external form, the lesions are easy to observe, but with internal BER, you might not notice until the fruit is cut open.
Blossom End Rot Symptoms
Tomato blossom end rot begins at the fruit’s formation stage, but the damage is not necessarily visible to the naked eye until the fruit begins to mature. Typically, the problem starts on the first flush of fruits and those that haven’t quite reached their full size. The spot appears irregular, watery and tan or yellowish-brown and will grow until it destroys much of the fruit.
BER usually shows up at the blossom end of the fruit, but can occasionally occur on the sides. (Lesions that occur on the sides look similar to tomato sunscald.) Over time, the lesion will spread, turn darker, eventually black, and the flesh will soften, while the fruit’s skin gets leathery. In essence, the fruit begins to rot at the end. The lesion may become infected with black mold. The disease makes the fruit unpalatable and also affects its appearance.
What Causes Tomato Bottom to Rot?
Blossom end rot can be a physiological problem or can be caused by unfavorable conditions such as freezing or drought, but in either case, the culprit is most often a lack of calcium, either in the soil or in the plant’s inability to take it up.
Calcium is responsible for strengthening cell walls and shoring up the tomato’s skin. When the tissues at the blossom end of the fruit malform, it allows pathogens to enter. Plants with accelerated, lush leafy growth seem to be most susceptible. In addition, other influences and stressors, such as drought or damage to the roots, can interfere with a plant’s ability to uptake calcium. Such stressors damage the cell membranes, resulting in the rot at the placental end of the fruit.
High temperatures and excessive sunlight are also contributors to BER in tomato plants. Calcium is transported up from the roots to the fruit by water, so if you’ve had a dry spell or haven’t sufficiently or consistently watered your tomatoes, you may see this condition develop.
How to Treat Tomato Blossom End Rot
A soil test prior to planting can prevent blossom end rot by indicating low levels of calcium. The test will also indicate high levels of ammonium and potassium, which compete with calcium for uptake. Here are some tips:
- Wait until your soil warms to 70 degrees F (21 C) before planting new tomatoes
- Use lime added to the soil 2 months before planting to provide a soil pH of 6 to 6.5.
- Avoid excess fertilizing, especially early in the plant’s development.
- Use fertilizer with a low nitrogen count such as 4-12-4 or 5-20-5.
- Consistent watering is key. As your tomatoes grow, make sure they’re getting a full inch (2.5 cm) of water each week, whether it’s from irrigation or rainfall.
- Place some organic mulch around the plants to retain moisture.
- Drench the soil around the roots with calcium nitrate or calcium chloride diluted with water.
More Blossom End Rot Tips
Never water from above, but always water tomatoes at ground level.
Overwatering can lead to root rot. Likewise, if the plants’ roots get dry or crowded by others, they won’t do their job of carrying up sufficient calcium.
Fruits afflicted with blossom end rot should be removed and discarded. Tomato end blossom rot will usually affect the first round or two of fruits. Although blossom end rot can leave the plant vulnerable to disease, it is not a contagious condition and won’t travel among the fruits, so unless you find you have a severe calcium deficiency, there’s no need for sprays or fungicides. Removing the affected fruit and continuing with a consistent watering schedule may clear the problem for the fruits that follow.
If you do find your soil is truly lacking in calcium, you can add a bit of lime or gypsum to the soil or use a foliar spray to help the leaves take up calcium. If you have an otherwise lovely tomato that’s rotten on the bottom, cut the rotted part away and eat the rest.
Heirloom varieties seem more prone to developing blossom end rot. Plum and pear shaped tomatoes are also more susceptible. Some varieties that are resistant to BER include Mountain Fresh, Mountain Spring, and Mountain Delight.
Looking for additional tips on growing perfect tomatoes? Download our FREE Tomato Growing Guide and learn how to grow delicious tomatoes.