Blossom End Rot in Tomatoes: Prevention & Cures

Growing tomatoes in containers and pots is a great solution if you are in need of space or have limited areas with sun.  Container growing does have its trials and tribulations however, and blossom end rot is a disease that is fairly common when growing tomatoes in pots. For additional tips (beyond blossom end rot) about growing tomatoes in pots click here.

Blossom End Rot is one disease that tomatoes are susceptible to when grown in pots.  It is initially a light tan, flattened area on the blossom end of the tomato which then enlarges and turns black and leathery. 

Prevention of Blossom End Rot

This disease is caused by a localized calcium and mineral deficiency in the developing fruit.  This deficiency is usually caused by an inconsistent watering regime, i.e., a dry-wet-dry cycle of watering. 

Tomato plants prefer about one inch of water per week, and if you allow them to get quite dry in the pots, and then deluge them with water when you notice wilting, you are setting yourself up for blossom end rot.

The following tips will help in preventing the disease:

1. Mulch the soil around the plant to reduce moisture fluctuations;
2. If rainfall is less than 1 inch per week, soak the soil slowly with water from a hose or set up a soaker hose (sprinklers or watering from above can splash soil onto the plant’s leaves and promote other diseases);
3. If you grow in pots each year, make sure and use fresh potting soil each year;
4. Select disease resistant varieties of tomatoes, and consider growing determinate tomatoes.  Determinate tomatoes are shorter and bushier than indeterminate and they do not continue growing until frost, so they do not vine and outgrow the trellis or stakes you may have in your pots.  With determinates you will get a lot of tomatoes over a 3 to 4 week period rather than fewer tomatoes over a longer period (all summer) as with indeterminates.  Most heirloom varieties are indeterminate, but a few examples of determinate heirloom varieties that grow well in pots are:  Raspberry Lyanna, Manitoba, Principe Borghese, Prescott, and Black Sea Man.  You can certainly grow indeterminate tomatoes (heirloom or hybrid) in pots, they are just higher maintenance;
5. Select plastic or fiberglass pots rather than clay pots.  Clay pots dry out too fast and it is harder to regulate the water regime.  A self-watering container, EarthBox Organic, Terracotta, or home-made wicking system is even better.

Other tips include not planting the tomatoes when the soil is too cool (affects early fruits), don’t overfertilize with nitrogen, and be careful not to injure the roots if cultivation is needed near the plants.

Some sources recommend calcium chloride sprays on the foliage but use caution with these. They can cause plant injury and some reliable sources say they don’t really help.

Possible Cures

All is not lost if your first flush of tomatoes has blossom end rot.  It is not a disease that lives in the soil like blight so it is certainly possible to save the remaining tomatoes. 

Follow these steps and you can still enjoy a large harvest for the remaining part of summer:

1. Set up a soaker hose system, transplant to a self-watering container, or be very conscientious about seeing that the pot does not dry out to less than 1 inch of water a week (and water the soil, not the leaves if using a hose or watering can);
2. While Calcium deficiency is one of the causes of blossom end rot, the idea of adding calcium to the soil is not necessarily the answer.

This paragraph from plantvillage.psu.edu summarizes the calcium issue very well:

“While blossom end rot is caused by a lack of calcium to the developing fruits, it doesn’t mean there isn’t enough calcium in the soil. It is most often related to an inconsistent amount of water in the soil or being taken up by the plant.

Calcium is brought to the fruit in the water the plant takes up from the soil so allowing the soil to dry out too much between waterings can cause blossom end rot. Pot-grown tomatoes are especially susceptible.” 

So, to sum up:  water management is the primary factor in preventing and curing Blossom End Rot on tomatoes. 

Happy Trails…….