How to Prevent and Control Blossom-End Rot on Tomatoes

Tomato growers need to take care to avoid blossom-end rot (BER), a disorder that can dramatically reduce fruit quality and quantity. Using a few simple irrigation and fertilization practices, damage from BER can be prevented or reduced. In this article, I will cover how to prevent and control blossom-end rot on tomatoes.

This relatively common garden problem is not a disease but rather a physiological disorder caused by a calcium imbalance within the plant. It can occur in pepper, squash, cucumber, melon fruits, and tomatoes.

What is Blossom End Rot

Blossom End Rot (BER): Blossom End Rot causes large brown or black dry or sunken spot(s) to appear, usually starting at the blossom end (opposite the stem) of the fruit. Fruits often ripen prematurely. BER occurs when a plant cannot metabolize the calcium it needs to develop correctly. This can happen when there is insufficient calcium in the soil or when root damage and water stress reduce the uptake and movement of calcium through a plant. Occasionally, BER is the result of excessive nitrogen fertilization. It only takes a day for a lack of calcium to affect fruit, and that day can occur any time after the blossom sets.

What Causes Blossom-End Rot?

Thankfully, blossom-end rot isn’t caused by a disease or pest. Instead, it results from a lack of calcium in the plant. This lack of calcium may be due to low calcium levels in the soil or—more often—soil that is over-or underwatered. When there are wide fluctuations in soil moisture, this reduces the plant’s ability to take up calcium from the soil. When the demand for calcium exceeds the supply, the tissues in the fruit break down, and blossom-end rot occurs.

In addition to watering issues, calcium deficiency during fruit formation may also be caused by:

Too much nitrogen-heavy fertilizer
Improper soil pH
High salt levels in the soil
Damage to plants’ roots

Being aware of these causes when caring for tomatoes and other garden plants is the best way to prevent blossom-end rot.

How to Identify Blossom-End Rot

Blossom-end rot first appears as water-soaked spots on the tomato's blossom end or bottom. The affected tissue breaks down rapidly, and the area becomes sunken, dark brown or black, and leathery. This can happen at any time as the tomatoes mature and most often on the first tomatoes of the season.

How to Prevent Blossom End Rot

Once the fruit has BER, it will not recover. However, the plant is still healthy. Remove the affected fruit from the plant. The fruit is still good to eat if you remove the affected part.
Blossom end rot most frequently occurs on fruit produced earlier and later in the season, when natural fluctuations in precipitation and cold weather occur.
To avoid BER, properly site and prepare your garden bed before planting. Most crops need full sun and loose, well-drained organic soil. Make sure soil pH is slightly acidic, between 6.2 to 6.8, for optimum nutrient uptake. Test your soil to see if calcium is recommended. If it is, apply lime in the recommended quantity according to the manufacturer's instructions.
Avoid planting too early in cool soils, inhibiting early root development, and making the plant more susceptible to BER. Start with a quality transplant: a healthy seedling with strong roots will make a healthy plant.
Avoid wide fluctuations in soil moisture by applying 2-3 inches of mulch. This will moderate the release of water to plant roots and keep the soil from drying out when it is directly exposed to the sun.
Avoid drought stress by ensuring your plants get at least 2 inches of rain or water per week. Apply enough water to moisten more than the top inch of soil. Container-grown plants will need more than 2 inches of applied water per week in hot weather; check them daily if possible. Consider using drip irrigation or soaker hoses. One or two soakings are better than many light waterings.
Avoid over-fertilizing during the early fruiting stage, especially if the fertilizer contains high percentages of nitrogen. Instead, use fertilizers specially formulated for tomatoes. These fertilizers have the right amount of nitrogen and other micronutrients best for fruit production.
Avoid close cultivation around the base of plants when weeding. A layer of mulch should help prevent the possible disturbance or damage of fragile roots accidentally.
Keep garden records: You may discover that some crop varieties are more susceptible to blossom-end rot than others.