There aren’t many more frustrating things than growing seemingly healthy tomatoes, those plants setting an abundance of flower and fruit, and then, once your tomatoes get about the size of a golf ball, having the fruit rot away from the base. This very common condition, called Blossom End Rot (BER), is caused one of two ways: by either a soil calcium deficiency or disruption of soil calcium uptake by the plant.  Fortunately, preventing BER from occurring and then realizing an awesome crop of tasty tomato fruit is relatively simple and home gardeners have a couple of possible preventative solution!

Blossom End Rot damage. Photo Courtesy Larry Williams, Okaloosa County Extension.

  1. Soil Test & Lime if Needed. The only way to really know if your soil calcium level is sufficient is through a soil test.  A complete soil test through the UF Soil Lab or other lab measures both raw nutrient levels and pH.  Testing for pH is especially critical.  For calcium, either already in the soil or in a supplement you apply, to be available to tomato plants, soil pH needs to be between 6.0-7.  In more “acidic” soil pH below 6, nutrients like iron and aluminum become more available to your tomato plants, outcompeting calcium for uptake into the roots. We don’t want that. If your soil test indicates a pH below 6, it will give a lime recommendation somewhere between 3-5 lbs/100 ft sq of garden area to raise the pH to the sweet spot between 6.0-7.0 where your tomatoes will thrive.
  2. Use a Non-Lime Calcium Supplement. If you’ve had your soil tested and your pH is fine, adding more lime as a calcium supplement isn’t helpful.  Using lime as an additional calcium source can actually lift pH above that 6.0-7.0 zone and cause other problems.  At this point, once pH is where we want it, I like to add a non-lime calcium supplement.  There are lots of options here.  Traditional fertilizers labeled for tomatoes and veggies tend to have a good calcium content in the 6-10% range and work great.  However, if you’re into organic gardening or just don’t need the extra nutrient value of a complete fertilizer, Gypsum is a good calcium supplement and is widely available.  Regardless of which non-lime source you choose, apply at planting or shortly after and follow label rates for best results.
  3. Water Properly. Consistent watering is key in helping ward off BER. Though we know BER is generally

    Healthy ‘Big Beef’ tomatoes grown in 2019 with a pH of 6.5, amended with Gypsum at planting, and watered regularly each day! Notice no BER. Photo courtesy the author.

    caused by calcium deficiency, it can be induced by creation of distinct wet and dry periods from non-regular watering, interfering with calcium uptake and availability to the plant.  So, while you may have adequate soil calcium, if you don’t water correctly, the condition will happen anyway!  It’s also good to keep in mind that mature tomato plants use large quantities of water daily, so during the heat of summer, plants in containers may need to be watered multiple times daily to maintain consistently moist soil.  Think about it, you don’t drink 8 glasses of water when you wake up and then never drink again throughout a hot day.  A tomato is no different.  Allowing your plants to wilt down before providing additional water ruins productivity and can induce BER.

Blossom End Rot, while one of the more destructive fates of tomatoes, is totally preventable by a little legwork early in the growing game from you!  Soil test and change pH with lime if needed, add a shot of calcium through a tomato blend fertilizer or non-lime supplement like gypsum, and water regularly!  Do these three things and you’ll be well on your way to a great crop of early summer tomatoes.  If you have any questions about tomato blossom end rot or any other horticulture or agricultural topic, please don’t hesitate to reach out to us at the UF/IFAS Calhoun County Extension Office.  Take advantage of this beautiful spring weather and get in the garden today!  Happy gardening.

Daniel J. Leonard
Latest posts by Daniel J. Leonard (see all)