Blossom-end rot can occur in tomatoes, peppers, cucumber, squash, and melons. Often times, the damage appears when the fruit is half-way grown. These soggy areas expand and turn dark brown and harden. The affected areas will begin to rot and the fruit should be cut-off and discarded.
Blossom End Rot is not a pest, parasite, or disease process but is a physiological problem caused by a low level of calcium in the fruit itself. There is no cure for blossom end rot, only prevention. This can occur when tomatoes are nutrient deprived or under erratic watering. Typically adding more nutrients will resolve the problem and tomato plants will recover.
How much nutrient are you giving your tomatoes?
The nutrient level should be increased when growing tomatoes upon the third feeding and moving forward.
Nutrient level for 6/7/9 pod gardens is 8 ml (2 capfuls) upon the first two feedings, and 11 – 12 ml (2 ½ to 3 capfuls) upon the third feeding and moving forward.
Nutrient level for a 3 pod garden is 4 ml (1 capful) for the first two feedings, and 6 ml (1 ½ capfuls) of nutrient upon the third feeding and moving forward.
Make sure that you are checking your water level every other day. Once the tomatoes are established, they will consume quite a bit of water daily, especially if you are running your furnace more often. Do not wait for your AeroGarden to alert you that your water level is low to add water. Your AeroGarden will alert you when the water level is very low. It is ideal to keep the water level in your garden to the "fill line", and to be consistent in your watering habits.
If you're starting to see Blossom-End Rot already, here's a solution. Start with a "rinse and refill". Empty the contents of your water bowl, rinse it, and replace the water adding the appropriate level of nutrient (12 ml). This will restore the pH level in your AeroGarden. Add 1 Tablespoon of Epsom Salt to the water. Remove and discard the browning tomatoes.
In addition, make sure you are pruning your tomatoes. Go ahead and prune back the leaves that are shading out your tomatoes. This will encourage your plant to continue to produce tomatoes. Also, your green tomatoes will be exposed to more light, encouraging them to ripen.