Are some of your ripening tomatoes developing dark brown or black on the bottoms? Let’s learn what is happening, and what we can do to eliminate it.
What you are seeing is called Blossom-end Rot, and it’s due to stress. Often that stress is from a nutrient deficiency – calcium is most often blamed – but not necessarily because there is not nutrition in the soil. There are many things that could be stressful to your tomato plants during this critical time of setting on and ripening fruit, especially when the weather is hot. Your job as gardener is to eliminate or at least reduce every possible stress factor.
We’ll start with calcium. Before planting your garden you should always apply natural mineral nutrients, including calcium, to your soil. This is explained in detail in the Fertilizer pages of the Learn section at www.growfood.com. It is very common for Blossom-end Rot to show up in July, two to three months after your tomatoes were planted. This is most likely because the large plants have used up the calcium that was added in the spring.
Here’s what to do: Add 1 ounce of lime or gypsum per foot of soil-bed between two rows of plants and mix it with the top inch or two of soil. Lime should be used if your annual rainfall is more than 20″, and gypsum is best in dryer climates. This is because lime raises soil pH (which “sweetens” acidic soil) and gypsum does not.
Also consider water as a possible factor. What are your daytime temperatures? If it is hot, that is a major potential stress. Do you water daily? When temperatures are above 90 degrees Fahrenheit you should water at least once each day, and if necessary, twice. Never let your plants even begin to wilt, as they are beginning to die, and you’ll see it in the fruit very quickly.
In addition to daily watering, in extremely hot weather some shade may be valuable – to reduce the stresses which cause Blossom-end Rot, as well as cracking of the fruit and lack of fruit set. You only want partial shade, and for only the hottest part of the day, so look for 25-30% shade cloth and place it above your plants to provide shade from about 11 A.M. to 3 P.M. And if you experience hot winds they will also certainly contribute to the problem. If possible provide a wind-break.
Lack of nitrogen is also sometimes blamed for Blossom-end Rot, but if you’re using a balanced mineral nutrient mix, such as the Mittleider Magic Weekly Feed regularly, that is highly unlikely.
Dr. Jacob R. Mittleider spent two growing seasons experimenting on this very problem during his last years living in Utah. He had been experiencing an unacceptably high incidence of blossom-end rot on the tomatoes in his own garden, so he worked diligently to find the cause. His results? Boron deficiency.
Now, that may or may not be the cause of your problems, but Dr. Mittleider determined that after 20+ years of growing, his ground had developed a boron deficiency, and after correcting it, his problem was solved.
I suggest anyone who sees blossom-end rot, who is doing everything else correctly, could apply 1 ounce (2 tablespoons) of 20 Mule-Team Borax to a 30′ soil-bed, and water it in thoroughly. Wait two weeks and if you see no improvement, do it again. After two applications, if the problem persists, the problem is something other than a boron deficiency.
Tomato Splitting
Stem-end cracks and radial splitting of tomatoes – sometimes called Growth cracks – happens during the last phase of growth and ripening. Stem-end cracks are usually caused by extreme conditions causing too rapid growth during ripening. Radial splitting is often also caused when extreme temperatures heat the tomatoes’ interior, causing it to expand and break the skin.
The reason it happens on ripening tomatoes is that the skin of green tomatoes is elastic and can stretch to allow growth and heat expansion, but it loses that elasticity when the fruit begins to change color and ripen.
Some varieties, such as the beefsteaks, are thought to be more susceptible to cracking than others, and Sweet 100’s are much more prone to this than Grape tomatoes.
Anything you can do to maintain even growing conditions will mitigate this condition – such as watering often, so that the ground never dries out, and small applications of a balanced fertilizer applied often (consider twice weekly applications of _ ounce per foot of Weekly Feed or other balanced natural mineral nutrient mix).
Extreme heat may still cause some cracking in spite of your best efforts, but always remember to maintain ideal conditions in every area within your control.
Cracked tomatoes are still edible but need to be used before infection by decay organisms enters the fruit and rots it.
If they continue to crack despite your best efforts, try picking them just as they begin to change color, and before cracking becomes a problem. Finish the ripening process in a cool, dry place. This may reduce the flavor somewhat.
