Do Tomatoes Need to Be Cooled at Mid-Day?

Climate

• Unless they are special heat- or cold-tolerant varieties, most tomatoes like temperatures between 55 and 95 degrees Fahrenheit, and will not flower or set fruit outside those temperatures. While almost any place can reach unfavorable temperatures for a day or two at one time or another, areas consistently colder than U.S. Department of Agriculture plant hardiness zone 3 are more likely to be too cold for longer periods – even in summer – and may require a greenhouse to successfully grow fruits. On the other hand, even in suitable zones, up to USDA zone 13, (USDA zone 11 in the continental United States) summer temperatures that soar past the 90s and stay there are not conducive to fruit set. On very hot days, misting tomatoes with cool water or using a high shade cloth during the hottest part of the day may bring temperatures down to a tolerable level.

Garden Location

• A south-facing slope in full sun may be ideal for making full use of a shorter growing season in a cool, northerly climate, but where days are hot and seasons are long, an east- or west-facing garden or one with some afternoon shade may actually work better. Planning your garden location to mitigate climate extremes and take full advantage of positive local terrain elements is a big first step toward ensuring garden success.

Growing Conditions

• If the sun is bright and the air scorching, cool soil can make a big difference in the way your tomato plants feel about producing. Growing tomatoes in deep mulch helps retain soil moisture and keeps your plants cool as the sun climbs. If you prefer to do away with the chore of keeping dry mulches neat and tidy, try growing a living mulch of non-competitive ground cover plants to shade the soil around the base of tomato plants, and keep soil evenly moist with a consistent watering schedule instead. Living legume mulches like annual hairy vetch (Vicia villosa) not only cool tomato roots, but also increase soil fertility and smother weeds simultaneously. You can grow hairy vetch simultaneously with tomatoes if you keep it in trim by partially “chopping and dropping” in place, allowing it to decompose on the surface to slowly add nutrients.

Other Cooling Tricks

• Professional horticulturist, Linn Mills of Las Vegas, suggests several cooling methods to trick tomatoes into production in hot desert climates. (See References 3) He suggests seeking out tomatoes that produce early, when temperatures are somewhat cooler, or buying those bred to withstand hot climates. Either of these strategies helps ensure that you get fruit before the season heats up unduly. Planting determinate varieties, which mature all at once and then die back, is another way to outsmart the heat. Planting them to get full morning sun but afternoon shade is yet another – and putting them in movable containers can make that trick easier still – especially if you don't have an ideal location.