Why Are My Tomatoes Not Flowering?

Improper Light

• Healthy tomato plants need eight hours of absolute darkness each night and about the same amount of sunlight during the day. Position plants in a south- or west-facing area of your garden where light requirements are best met. Thin, tall plants that fail to flower are usually sunlight-deprived. Move plants to a location with better access to sunlight or provide supplemental lighting when grown indoors.

Unsuitable Temperatures

• Proper temperatures play a role in whether or not tomato plants flower. Tomatoes prefer day temperatures of 70 to 76 degrees Fahrenheit and night temperatures between 65 and 72 degrees. They can't tolerate frost. Exposure to extreme cold temperatures can delay flowering and, in certain cases, prevent it from happening at all. Never plant tomato plants outdoors until the threat of frost has passed. Propagate tomatoes outdoors at least three weeks after the last expected frost. Conversely, high temperatures above 90 degrees can impact flowering. Increase irrigation to tomatoes during periods of hot weather.

Overfertilizing

• A common mistake made by home gardeners is feeding tomato plants too much, notes the Ed Hume Seeds website. Although nitrogen, a nutrient found in most commercial garden fertilizer, enhances plant growth, giving plants a fertilizer with high concentrations of nitrogen can cause them to grow tall at the expense of flower development. Don't feed tomato plants after the soil has been prepared for planting unless plants display clear signs of stress, like leaf discoloration and hampered growth. If you must feed plants to restore their health, provide them a fertilizer formula with low nitrogen amounts and supply plants with only half of the suggested amount.

Remedies

• Tomato plants occasionally need to undergo a brief period of stress to jump-start their bloom period. Provide tomato plants slightly less water for a week or two and hold out a week more than planned to apply fertilizer. Sometimes temporarily withholding water and nutrients is enough to prompt blossom set. Modify your pruning regimen to encourage flowering. If you started pruning plants, suspend trimming for one or two weeks or until flowering occurs. If you haven't pruned yet or pruned very little, start removing excess growth. Plants that expend too much energy growing foliage might not have enough energy left to bloom.