This time of year many people are experiencing a very common plant disease called Blossom End Rot where the bottom of their fruit is turning black and seems to be rotting away. And that is exactly what it is doing, it is rotting from the calyx end of the fruit where the flower blossom was attached and typically appears as the fruit begins to mature and ripen.
This commonly happens to tomatoes, but it is not limited to just tomatoes. Zucchini, squash, peppers, cucumbers, melons, apples, pears, etc., can all suffer from blossom end rot, and it is always caused by the same thing, a lack of calcium in the plant, however, there may be more than one reason for it.
Most people will immediately think they have to add calcium to the soil when they see this happen, but a lack of calcium in the plant does not necessarily mean that there is a lack of calcium in the soil. There may be plenty of calcium in the soil but it was unable to get into the plant.
For years people have been swearing by using Epsom Salt to prevent blossom end rot on their plants, however, this is a myth that just refuses to die and over the years has cost countless gardeners their precious harvests. Not only does Epsom Salt not work to prevent blossom end rot, it actually makes the situation much worse.
Epsom Salt is NOT calcium, it is magnesium sulfate. Before I get into the science of the problem, let's use common sense for a second. If you have a lack of calcium in the plants, how would adding magnesium sulfate to the soil resolve the issue? Blossom end rot is not caused by a lack of magnesium.
I know what you are saying, "How does magnesium in the soil lead to more blossom end rot?" Both calcium and magnesium are taken into the plant in the same way, through the roots in water. To the plant, both calcium and magnesium are indistinguishable. Adding magnesium into the soil lessens the amount of calcium that the plant is able to take up because it is now getting more magnesium instead so the amount of calcium the plant is able to intake is further reduced.
The most common cause of blossom end rot is not a lack of calcium in the soil, but a lack of regular watering. When the plants are not watered regularly, they are not able to uptake the nutrients they need to thrive, which includes calcium. If the soil is left to dry out between waterings, it is like turning a switch on and off, limiting when the nutrients can get to the plant. The best way to prevent this from happening is by doing regular deep waterings when the plants need it, not when the soil is already bone dry.
Covering all of the soil under the plants with a thick layer of mulch can also prevent blossom end rot by helping to prevent water in the soil from evaporating too quickly on hot days. The mulch layer also helps to prevent other plant diseases caused by fungal spores in the soil which get splashed up onto the plant leaves while watering.
Once you see the signs of blossom end rot, adding calcium to the soil will not help because the plant is already in desperation mode. A liquid calcium supplement can be used as a foliar spray by mixing with water and spraying directly onto the plant leaves. The plant does not have time to wait for a slow acting soil fertilizer to take effect.
You can purchase an expensive liquid calcium supplement from a garden supply center, but why do that when there is a cheaper alternative available for a fast-acting calcium supplement that you may already have in your home right now?
The Tums antacid tablets (or generic brand) that you probably already have in your medicine cabinet is a fast acting form of calcium that can be available to your plants immediately.