Disorder name: Blossom-end rot
Cause of disorder: Calcium deficiency often associated with dry soil conditions
Hosts: Blossom end rot is common on tomatoes and peppers, but can occur on other produce, including eggplant, zucchini, and melons.
This type of rot is not a disease and cannot be spread from one plant to another. It is caused by a calcium deficiency.
Symptoms
Blossom-end rot results in the bottom of the tomato turning black and sometimes almost leathery.
The bottom of the tomato is called the blossom end, because that is where the flower or blossom was connected.
The small dark spot on the bottom of the tomato marks where the flower was.
Disorder Development
Blossom-end rot is caused by a calcium deficiency. Calcium is an important building block of the cell walls within every plant. When it is deficient, the cell walls don’t form properly and the cells collapse.
Blossom-end rot does not always mean that there is not enough calcium in the soil. It means that the calcium is not making it all the way to the bottom of the tomato.
Illinois soils are generally not deficient in calcium.
Improper watering or very dry weather are often the reasons that calcium doesn’t get to the bottom of the tomatoes.
Water carries calcium from the soil into the plant. If water is lacking, the calcium can’t be delivered.
Plants should be watered deeply to get water down into the soil profile, so it is available to be taken up into the roots. Shallow, frequent watering does not get water deep enough into the soil.
Watering every day is not needed for in-ground gardens. Water plants when the top inch or so of soil is drying, then water thoroughly. Depending on weather, watering could be done every four to seven days.
Container-grown tomatoes are the exception. They most likely will need to be watered every day due to the small volume of the container. Water containers enough so that some water comes out the drainage holes in the bottom of the container. Container-grown tomatoes often get blossom-end rot because it can be difficult to maintain adequate water in containers during hot weather. Also, unlike our garden soils, potting mixes for containers may need to have calcium supplements added.
Management
Cultural Management
Proper watering techniques are often all that are needed to prevent blossom end rot. Remove affected tomatoes so that they do not divert calcium from unaffected ones.
Chemical Management
Container-grown tomatoes may need to have calcium supplements added to the potting mix.
For more information, contact The Morton Arboretum Plant Clinic at 630-719-2424 or plantclinic@mortonarb.org.