1. Good soil is a must with all vegetable gardening for producing healthy lettuce leaves and other vegetables. Give them lots of nutrition by keeping the nitrogen level high with the use of a good 30-10-10 NPK (nitrogen, phosphorous, potassium) fertilizer.
2. Plant the seeds about 1/8-3/8 inch deep, separated by 6-12 inches from the next plant. Use a graduated yard stick if in doubt about the measurements. Romaine does fine at the smaller spacing, but crisp lettuce needs more room. If you plant in rows, keep the rows separated by about 20 inches. Keep in mind that seeds shouldn’t be planted too early, since they’re subject to cold damage.
3. Keeping the soil moist but not soaked is good. Lettuce doesn’t have very deep roots, so it needs to find moisture near the surface. Still, try to keep the water off the leaves and onto the soil, use a soaker hose for the best results, except for the occasional washing after a hard rain splashes mud on the leaves. Wet leaves encourage disease, especially when they’re moist during nighttime temperatures.
4. Since their roots aren’t very deep you’ll also need to be diligent about weeding around lettuce plants. Many grasses and other plants can compete well because their roots go down to deeper soil. Infrequent but deep watering, letting the top layers dry out, will give most an advantage. But lettuce doesn’t have that advantage, so you’ll need to help them.
5. Like most vegetables, lettuce plants also have problems with diseases and pests. In their case, the variety is quite large. Many insects find the leaves irresistible and the folds offer many places for fungi to grow.
6. Aphids, flea beetles and leafhoppers are common problems. Slugs are even more so. Cutworms are often seen. Washing with a high pressure hose can help temporarily, but be sure to do it early to give the leaves time to dry before nightfall. A good insecticide (safe for human consumption) and lightly applied will keep them under control for the long term.
7. Anthracnose (Microdochium panattonianum) is a common fungal disease. It can stay alive in unplanted soil for many years, so don’t assume you’re safe because your garden is new. Bottom rot (Rhizoctonia solani) is another common fungus. It occurs usually in soil that drains poorly. Keeping the foliage dry and planting in good soil will help to reduce the odds of being infected.
8. Bolting (to flower and produce seeds earlier than expected or wanted and the leaves stop growing) is a common problem with lettuce, and it isn’t a disease or pest, though it can be worsened by them. Lettuce likes cool weather and bolting is more common when the temperatures are consistently too high. Keeping the plants shaded will help. One way to do that is to plant a shading crop, like corn , over the lettuce.