Temperatures too cold or too hot; weather too dry or too wet; soil too nutrient rich or deficient; these are reasons tomatoes and peppers drop their blossoms.
Here are reasons for tomato and pepper blossom drop and what can be done:
• Night temperatures below 60°F. Cover plants with floating row covers or plastic tunnels until temperatures warm. Wait to set out plants until night temperatures are warmer.
• Daytime temperatures above 85°F. Put shade cloth structures over plants to protect them from direct rising temperatures. Irrigate planting beds with cool water. In hot summer regions, time planting so that plants flower and set fruit before average daytime temperatures are too warm.
• A sudden shift from hot spell to cool temperatures. If cool temperatures are forecast, protect plants with floating row covers or plastic tunnels.
• Low soil moisture as a result of drought or lack of irrigation. Keep the soil evenly moist; avoid letting the soil go dry, and avoid overwatering to compensate for not watering. Work moisture retentive aged compost into planting beds.
• Too much soil moisture as a result of rain. If summer rain is frequent, plant in well-draining raised beds or grow plants on mounds. Spread plastic around plants so that excess water runs off into furrows.
• Hot, dry wind. Plant or erect wind breaks to keep winds from reaching the crop. Plant a dense hedge upwind of the garden or erect a windbreak or fence.
• Too much nitrogen in the soil. Excess nitrogen can cause rapid, succulent growth and disrupt a plant’s metabolism. Avoid high nitrogen soil additives such as bloodmeal and fresh manures. Use low nitrogen fertilizers such a weak compost tea or side-dress plants with aged compost, a balanced soil amendment.
• Too little nitrogen, potassium, or phosphorus in the soil. Give plants an even fertilizer—not too much nitrogen, phosphorus or potassium. Work aged compost into planting beds twice a year; the nutrients in aged compost are evenly balanced.
• Tarnished plant bug. The tarnished plant bug feeds on vegetable flower stems. The tarnished plant bug is ¼ -inch long, oval, flat and brownish. Control this bug by spraying with pyrethrum or dusting with savadilla.
• Verticillium and fusarium wilt. Fungal diseases leave plants stressed and fighting to survive; blossoms drop as the plant fights to overcome disease. Prevention is better than cure when it comes to disease: make sure soil is well drained; avoid overhead irrigation; space plants allowing for air circulation; eradicate weeds; remove and destroy infected plants; don’t plant members of the tomato and pepper family in the same spot two years in a row once disease hits.
Let plants set blossoms again. Tomato and peppers that suffer from environmental stress and drop their blossoms but do not succumb will commonly blossom again and set fruit once conditions improve. If plants experience early season or unexpected stress, give them optimal growing conditions as best you can and allow them to grow on. Many short-season or early-season tomatoes and tomatoes bred for hot summers are predisposed to resist early season stress and blossom drop. Tomatoes that resist blossom drop include Big Early, Floramerica, Hot-set, New Yorker, Porter, Red Cherry, Tiny Tim, and Walter.