Why does my lettuce taste bitter?
Written by
Benjamin Miller
Reviewed by
Prof. Martin Thorne, Ph.D.Bitterness in lettuce results from stress on the plant, and the time of harvesting. Old leaves can become quite bitter tasting due to the plant's increase of defensive chemicals. One community garden we help manage experimented with picking lettuce before noon, showing a reduction of 30% in bitter compounds over-harvesting afternoon. Heat waves can speed this up by increasing levels of lactucin during this time.
Harvest Timing
- Pick leaves before 10 AM
- Use shade cloth above 75°F (24°C)
- Check size daily during growth spurts
Soil Management
- Test nitrogen levels biweekly
- Add crushed eggshells for calcium
- Maintain 6.0-6.5 pH range
To help alleviate heat stress and bitterness in lettuce, consider container gardening. My 12-inch (30 cm) self-watering pots provide a consistent 65°F (18°C) temperature for root zones, even during heat waves. To create a barrier for temperature, line your containers with burlap. In my July trials, this method produced leaves that were sweeter than those grown in the ground, even with high heat conditions.
Different watering styles can significantly influence flavor. Deep soak your beds until water accumulates around 1 inch (2.5 cm) above the soil line - this prompts root penetration of 8 inches (20 cm). Watering in the morning is also effective at reducing midday evaporation. Drip lines should be installed at 6 inches (15 cm) spacing to ensure that moisture is distributed evenly.
Plant nutrient solutions can save bitter crops. A foliar spray of kelp and molasses applied weekly can ameliorate bitterness. Prepare a mixture of 1 tbsp (15 ml) kelp extract with 1 tsp (5 ml) molasses per gallon (3.8 L) of water. Use this foliar spray at dusk for best absorption into the leaf tissue.
Read the full article: How to Grow Lettuce: Expert Tips for Every Gardener
