To grow robust, juicy tomatoes in the foothills, gardeners may need to protect plants from scorching August heat. Tomatoes generally thrive in full sun and warm weather, and some newer varieties can even withstand intense evening heat. But when nighttime temperatures remain above 75° F, blossoms often drop off tomato plants and fruit production stops.
Too much nitrogen fertilizer can result in overly vigorous vine growth and blossom drop. Intense sunlight can cause sunscald spots on tomato fruit. Sunscald blisters eventually turn grayish-white, forming a paper like surface. To protect fruit, try draping cheesecloth over the vines in mid to late summer, or train vines to a cage to shade developing fruit. Training the vines makes it easier to pick tomatoes, and it reduces fruit rot that can develop when tomatoes touch soil.
Avoid water stress. Under-watering plants during bloom can result in blossom end-rot, a leathery, brownish rot that occurs on the blossom end of the fruit. Excess nitrogen, calcium deficiency and salt accumulation in soil can aggravate the problem. Mulching soil around the cage with straw will reduce evaporation and ensure a more even supply of moisture to the plant.
Fluctuations in soil moisture can also cause split fruit or growth cracks. Hot, dry weather can lead to tough, leathery skin on the tomato fruit. Alternating moist and dry soil conditions may result in bursts of growth in fruit, causing the stiff leathery skin to crack. Mulching the soil will even out soil moisture and reduce weed problems by shading the soil and preventing weed seed germination.
This article adapted from Cooperative State Research, Education and Extension Service, USDA. Please contact Ken Churches at firstname.lastname@example.org or (209) 754-6475 with your agricultural questions. To speak with a Certified Master Gardener: Calaveras (209) 754-2880, Tuolumne (209) 533-5696, Amador (209) 223-6837, El Dorado (530) 621-5543.