Question: I am having a problem with some tomato plants in my back yard. The plants are growing good and strong and small green tomatoes are begging to grow. I looked at the bottom of one tomato and it is turning black. Can you please tell me what is causing this. There are several tomatoes on the vines of this plant, but only one tomato has this black section on it.
- George K.
Answer: Hi George,
Your black bottomed tomato sounds a lot like blossom end rot. I don’t have a picture of it to post but a quick search will bring up countless photographic evidence for identification. The reason I am ruling out other problems is because you describe your plants as healthy. Blossom end rot appears as a blackened, sunken spot on the bottom of green or ripening fruit. The plant itself rarely shows any signs of a problem. In fact some stricken fruit is found growing on plants that are exceptionally leafy and health. This particular brand of the condition is a symptom of excessively fertilizing with a high nitrogen fertilizer. In that case, much of the plant’s energy goes into producing big, healthy leaves, leaving little else for fruit production.
Blossom end rot is a very common condition said to be caused by a calcium deficiency, however in general the problem is not caused by a lack of calcium in the soil but inconsistent watering, drought, and uneven soil moisture making it difficult for the plant to draw nutrients up through the roots.
From your description it sounds like your tomatoes are growing in-ground however this problem is especially common for container grown plants since containers dry out quickly and can be difficult to keep consistently watered.
The good news is that the problem is easily fixed — future tomatoes grown on the same plant aren’t doomed to be diseased if you follow the advice below.
General Tips to Avoid Blossom End Rot
- Amend poor soil by adding lots of organic matter like compost. This will provide better nutrition for the plants and make for soil that holds moisture well.
- Water tomatoes deeply, but less frequently. This means give them A LOT of water when you do water rather than watering regularly but in small quantities.
- Water more often once your plants start to produce fruit, continuing to water deeply each time. Tomatoes are a watery fruit, your plant will need lots to grow healthy fruit.
When Excessive Nitrogen is the Problem
- Cut back on high nitrogen fertilizers like fish emulsion.
- Add kelp meal or liquid seaweed to ergular waterings. You can even spray the blossoms with this mix when they first open.
Tips for Container Gardeners
- When growing in a container, grow only one tomato plant per pot.
- Choose a container that is appropriately-sized for the plant. Small busing and dwarf tomato plants will do in a hanging basket but most tomatoes have very deep and ample roots requiring lots of space. Garbage bins are the way to go.
- Grow tomatoes in plastic pots when possible. Plastic retains water much better than terracotta, a difference that will become much more noticeable at the peak of summer drought.