Why isn't my lettuce forming heads?

Not forming heads might be the most maddening lettuce failure of all! The plants skip right over heading and bolt to seed. Still, head formation is spurred by cool temperatures, consistent moisture, fairly close planting, and balanced nutrition. Fix those early, and I've saved many a crop.

They can bolt if you have unseasonably hot weather, so choose more heat-tolerant plant varieties. Romaine and butterhead types typically perform better than iceberg lettuce. These can be planted in spring or fall, but avoid the hot days of summer. Use shade cloth when the weather is consistently over 21°C (70°F). I get along well with the summer joy types, such as 'Summer Crisp', during the warm months.

Adjust your watering system to deliver consistent moisture. Rainfall levels may provide no water for several weeks. Lettuce requires about 2.5 cm (1 inch) of water per week. Mulch the soil with straw to minimize evaporation. Stick your finger into the ground about 5 cm (2 in) deep. If dry, water. This stress will definitely stop head formation in lettuce. The younger plants are most susceptible, but I have eliminated this with my drip system.

What is adequate spacing? Space head lettuce 30 cm (12 inches) apart for each plant. A crowded plant is competing with its neighbor, and neither plant can fully develop, as the leaves are crowded and cannot open further to receive air and light. Seedlings must be thinned early. For growing in containers, and for a single plant, a pot of at least 20 litres is required. (5 gal.) Capacity will be required.

Test your soil before planting. Lettuce requires nitrogen for leaf growth and some phosphorus for root development. Amend accordingly with compost or 10-10-10 fertilizer at the time of planting. You may also want to side-dress every four weeks. Don't go too heavy in the nitrogen, or you will have soft lettuce heads. Well-balanced nutrition means firm, tight heads every time.

Read the full article: When to Harvest Lettuce for Best Results