Tomato Problems

June is still alive and well and, for us gardeners, many tasks demand our attention: weeding, mulching, watering, fertilizing, and pest control to name a few. It’s prime time for our long sought after vegetables — they are maturing and tomatoes are beginning to ripen on the vine.

Speaking of tomatoes, it is time to seriously address the issue of blossom end rot. Caused by a lack of calcium in the developing fruit, blossom end rot can be caused by one or more of the following: (1) extreme fluctuations in soil moisture (from very wet to very dry), (2) rapid plant growth early in the season, followed by very dry weather, (3) excessive rains that smother root hairs, (4) high levels of soluble salts (from fertilizer in the soil from over fertilization,) (5) cultivating too close to the plant, and (6) a deficiency of calcium in the soil. It is to be noted that, even if calcium is in ample supply, due to calcium’s poor mobility throughout the plant, deficiency symptoms can still appear. To be sure, blossom end rot is a calcium issue.

To prevent blossom-end rot, follow these guidelines: (1) maintain uniform soil moisture as much as possible by mulching and watering wisely. Apply enough water at each irrigation to wet the soil to a depth of 18 to 20 inches. Water when the soil two inches deep is barely moist; (2) avoid using high nitrogen fertilizers. Using 5-10-15 instead of 10-10-10 would be advisable. Also avoid the use of fresh manure in large amounts. Use nitrogen in the form of potassium nitrate or calcium nitrate and avoid ammonium nitrate (34-0-0) if possible, since ammonia tends to inhibit the uptake of calcium. Applying several small side dressings is also better than applying a large amount of fertilizer at one time; (3) plant in a well-drained soil. Roots cannot thrive in a water-logged soil. A healthy root system supported by a well-drained soil is better able to take up calcium and deliver it to the tomato fruit; (4) avoid cultivating deeper than one inch within one foot of the plant so as to avoid destroying valuable feeder roots.

Another problem of tomatoes is poor fruit set. Plants may be quite lush and healthy, but little or no fruit develops. Why? There may be several reasons, including: (1) extreme temperatures: once daytime temperatures rise above 90 degrees or nighttime temps exceed 75 degrees or fall below 55 degrees, most tomato varieties stop setting fruit, even while continuing to produce flowers. Plants may also drop blossoms. Among the few varieties that are able to take the heat are the old southern standbys Homestead and Atkinson. Others include Solar Set, Mountain Supreme, Sweet 100, Florida 91, Sanibel, Summer Set, Heatmaster, and Solar Fire; (2) dry soil: blossoms dry and fall off when plants are under extreme drought stress; (3) shading: few blossoms are produced when the plants receive too little sunlight, which is anything less than about six hours of sunlight per day; and (4) excessive nitrogen: high levels of nitrogen in the soil, from too much fertilizer, encourage beautiful, lush leaves at the expense of blossoms and fruit.

To prevent poor fruit set, try the following: (1) water tomatoes regularly, never allowing the soil to completely dry out. Mulch with straw, black plastic, or other materials to maintain uniform soil moisture, and (2) plant tomatoes in an area that receives at least six hours of direct sunlight per day. If your yard is shady, consider growing some tomatoes in containers on your porch or patio; (3) feed tomatoes with a potassium rich feed such as superphosphate (0-20-0) or a brand of 0-10-10 as the flowers and fruits begin to form; (4) remember to back off on the nitrogen after the first blossoms form.

Good luck as you tend your prized tomato plants this month!

Tim Lewis is a Georgia Green Industry Association Certified Plant Professional, gardening writer, former Perry High School horticulture instructor, and former horticulturalist at Henderson Village and Houston Springs. He and his wife, Susan, own and operate Lewis Farms Nursery located on Hwy 26 two miles east of Elko, where he was born and raised. He can be reached at (478) 954-1507 or timlewis1@windstream.net.

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