You’ve heard about Blossom-end rot, but have yet to see it. Or, you’ve experienced it, and just did not know what it was. Hopefully this article will clear up the murky waters of one of the most common tomato diseases to occur, and, armed with this knowledge, you may be able to prevent it from happening, though even the most experienced gardener has seen it on their tomato plants. (It also occurs on pepper plants and on eggplant, though it may start on the sides, near the blossom end, on these vegetables.)
First, you need to be able to identify it, and the name itself creates no small bit of confusion, especially for novice gardeners. The blossom end of the tomato is so-called because as the tomato grows, it actually emerges from under where the blossom was. The fruit grows between the calyx and the blossom, the calyx being the modified leaves you see at the top of the tomato. You will see the brown end of the blossom at the bottom of the growing tomato, not at the top where it is attached to the stem.
Blossom-end rot will start as a small beige or tan patch on the blossom end of the tomato while the fruit is still green, often appearing water-soaked. And then it becomes sunken and turns leathery and dark brown or black as the fruit matures. It looks really, really ugly and rather disgusting, but you can eat the parts of the tomato that are not affected, as long as no secondary pathogens or pests have invaded the lesion and spread throughout the rest of the fruit. In severe cases, the whole fruit is a loss and it is not uncommon to lose 50% of the fruit on your tomato plants to this curse. I wouldn’t recommend giving these unattractive fruits away, even if the upper part of the tomato is edible. Better to use them in salsa, make tomato sauce, or at least slice them before anyone can see what they look like, discarding the rotted portion, of course.
To prevent blossom-end rot, you need to know what causes it. Blossom-end rot is caused by a calcium deficiency, which is required in fairly large quantities for normal cell growth. Blossom-end rot results when the demand for calcium exceeds the supply, which can be caused by…
- Moisture fluctuation, which can reduce a plant’s calcium uptake.
- Low calcium levels in the soil, often the result of improper soil pH.
- Drought stress.
- Over fertilizing with nitrogen-based fertilizers, which causes rapid vegetative growth, but does more harm than good when the plant starts to bear fruit.
…and which can be prevented by:
- Maintaining the pH of your soil right around 6.5. An inexpensive soil tester can quickly give you the pH of your soil, and then you can take the necessary steps to adjust it. This is not only good for preventing blossom-end rot; it is beneficial to the majority of your garden plants. 6.5 is the recommended soil pH for successful organic gardening.
- Maintaining consistent moisture for your tomato plants. All garden plants require about one inch of moisture per week. If you are fortunate enough to have plenty of rainfall, this will not be an issue, unless you are getting way too much. Otherwise, irrigation is necessary, and I recommend a drip irrigation hose. A drip irrigation hose ensures that the moisture is going to the roots where it is needed, not landing on the leaves (especially in a crowded garden) and then evaporating.
- Avoiding nitrogen-based fertilizers as your tomato plants start to fruit. There are actually two kind of nitrogen fertilizer available. Nitrate nitrogen is preferable to ammoniac forms. Excess ammonium ions can reduce the calcium uptake of your plants. All nitrogen fertilizers should be used lightly and with the knowledge that the run-off from synthetic fertilizers can pollute water sources, including wells and ground water and are not entirely safe for use around your family, children and pets.
- Ensure adequate calcium levels in your soil. Applying lime to your soil is one way to add calcium, but it will also lower the pH. This would be the ideal solution if you also need to adjust your pH down. Additionally, you can use a product, such as Nutri-Cal® Liquid Calcium supplement. Highly concentrated, it is applied in a fine spray every couple of weeks, though root absorption of calcium will be the most beneficial. Some gardeners crush egg shells and mix it into the top inch or so of soil, right around their plants, experiencing quite a bit of success, though the exact amount of egg shell needed is not really known.
- Using good, rich soil is the ultimate way to prevent blossom-end rot from occurring. Soil rich in organic matter is naturally rich in calcium, and is also much more able to retain moisture, which means maintaining your soil’s moisture content is much easier. You can mix compost into your soil prior to planting or you can even top-dress your soil and as you water and cultivate, the compost will become mixed with your soil. Worm Castings are also a source of the richest organic matter and can either be mixed in, top dressed or side dressed.
All of this may sound like a lot, but the truth is that these are fairly easy steps to making sure that all of your garden plants grow healthy and strong. Good gardening habits go a long ways to ensuring not only a productive harvest, but less effort on your part, in the long run. In particular, that your tomatoes are not lost to blossom-end rot. That would be a tragedy! We all know how much we love those fresh, home-grown tomatoes and you can hardly afford to buy them in the grocery store anymore.
Happy Gardening Everyone!