One very common problem that I have seen more of this year than in the past several years is blossom end rot. I am answering calls almost daily about blossom end rot that affects not only tomatoes but other vegetables such as peppers and watermelons as well. Blossom end rot is not a disease but rather a physiological disorder resulting from calcium deficiency. This disorder is marked by a dry black leathery rot at the bottom (blossom) end of the fruit, hence the name blossom end rot.
The best solution to blossom end rot problem is to make sure you keep the garden well limed with agricultural or dolomitic lime. During dry weather plants cannot take calcium up out of the soil very well even if we have applied lime, so keeping plants well-watered by using drip or soaker hoses will help to reduce the incidence of blossom end rot. I also recommend using a good layer of mulch such as pine or wheat straw, shredded newspaper, or other organic mulch. The mulch will help to hold water in the soil around your plants and will help to keep the soils moisture at an even moisture level as opposed to being wet then dry then wet again. It will also help to reduce the amount of water it takes to provide your plants with adequate moisture.
If blossom end rot has already affected your garden, you will need to remove the effected fruit as they will not recover from blossom end rot. The effected fruit will serve only as an entry point for other disease and insect problems. While most fruit that have blossom end rot develop the disorder while they are very small, the larger fruit may still be used by simply cutting away the effected part. If the tomatoes that you remove are large enough to use, then they certainly can be (the blossom end rot does not affect the edibility of the fruit). If they are large enough, it is as good of an excuse as any to fry up a pan of fried green tomatoes after you have removed the bottom end of course.
Our potted or “patio tomatoes” are very prone to develop blossom end rot. Many of the calls that I have gotten this year about blossom end rot have been either in potted tomatoes that we enjoy having on our patios and other such areas and also in raised beds which are very popular now days. There are several reasons for this. First of all, much of the potting soil and other materials that we use to pot the tomatoes in have a very low calcium content to start with. Secondly, our potted plants and raised beds tend to dry out much quicker than traditional “in ground” gardens. Again, the plants will not take up calcium, even if it is present, when the potting soil is dry.
For potted or containerized tomatoes, I recommend adding about a cup of dolomitic lime to the potting mix when you plant your tomatoes. The lime will help reduce the pH or acidity of the potting mix as well as to add calcium which the plant needs as it grows and produces fruit. Also make sure that you keep you potted tomatoes (or raised bed tomatoes) adequately watered to help them actually take up the calcium that you added. On my larger pots, I even mulch them with pine straw just like I do for the in-ground tomatoes growing in my garden. The mulch will help to hold moisture better and prevent drying out as well as to help moderate the temperature of the potting media. Our containers are fairly small (as compared to garden grown tomatoes anyway) and often times dark in color which translates into a lot of heat generation and retention which can actually damage the plant’s root system.
Although there are many calcium chloride sprays commonly sold, the fact is that the single best way to help prevent blossom end rot is by good soil nutrient and pH management and proper watering and mulching. Calcium chloride sprays are mixed with water at labeled directions and sprayed on the foliage of the tomatoes. This can have a couple potential problems. First of all calcium is not easily absorbed through the foliage, especially the older foliage. Secondly, too much calcium chloride spray or spraying at really high temperatures can cause leaf burn and plant damage. The research on such treatments is very varied as to the final result, so if you choose to use one of these sprays always do so by following the directions on the label, avoid spraying at high temperatures, and always combine such treatments with proper watering, liming, and mulching.
Sidedressing your tomatoes with calcium nitrate fertilizer is another way to get added calcium into your soil. As with any sidedress fertilizers though, be careful about “over doing it” as many of us home gardeners are prone to do. Plan to use about three pounds of calcium nitrate per 100 feet of row space when the fruit is about one-third mature size. Adding too much can result in poor fruit set or any of a number of other problems.