Lettuce is a cool season green that grows best in Kihei when planted in the late fall through early spring. In my opinion, the night time temps are the most important factor in growing lettuce successfully. If they're too warm, germination may be low or non-existent and the plants may bolt early in their growth cycle.
A Baby Romaine Mix
Growing lettuce as cut and come again baby greens is perhaps the best method for achieving good results. Seeds are sown densely and if some fail to germinate it's not normally noticeable.The lettuce is ready to begin cutting in just a few weeks.
If you create your own mesclun mixes, I suggest not adding kale seeds into the mix as kale grows large leaves much faster than lettuce. Mizuna and other small mustard greens work well in a mix with lettuce seeds.
I've trialed more varieties of lettuce than I can remember, looking for lettuces that will grow as individual plants in our warm climate. So far, Bronze Arrow, Green Romaine and Tango have been the most heat tolerant but Bronze Arrow doesn't produce much bronze or red pigment in the leaves.
New Red Fire
Many of the red lettuces need cooler weather in order for the red to develop. The winter temps fluctuate and my results with the red lettuce varies each year. New Red Fire and Mascara developed some red and violet variegation.
At least Merlot has consistently produced deep red-violet leaves.
For individually planted lettuce, I've found that looseleaf, oakleaf and romaine are more heat tolerant than batavian or butterhead. I've yet to grow a butterhead variety that actually formed a head. Lettuce tends to bolt early. Most of the full heads I've harvested have been on the smaller side and this is due to our warm climate.
Individually planted lettuce seems to grow larger in full sun but will grow in partial shade.
A Baby Lettuce Mix at 10 days
All of my lettuce is grown in containers. For cut and come again baby lettuce, I plant seeds in an 8 in x 30 in container with a soil depth of 5 inches. For individual lettuce, I plant in a container with a soil depth of at least 7 inches.
I fill the container with an organic potting soil amended with OMRI azomite and green sand. After the lettuce has been growing for 3 to 4 weeks, I begin watering it with liquid fish emulsion every 2 weeks.
Another container I use for lettuce is a 3 ft x 2 ft x 7 in all purpose utility tub that I purchased at Kihei ACE Hardware for about $22. I drilled holes in the bottom and each fall when I plant lettuce I fill it with fresh potting soil amended with OMRI azomite and green sand. In this container I grow rows of small lettuces.
Densely Planted Rows of Lettuce
I plant the seeds in rows that are spaced about 4 inches apart and gradually thin the seedlings to 5 per row. I've been able to grow this lettuce in partial shade - it's in full sun until 12 pm, diffused sunlight through the early afternoon and shade in the late afternoon. It's a great way to trail a number lettuce seeds at the same time.
Slugs, snails and the cabbageworm are pests that affect lettuce and many other salad greens. I keep lettuce covered with a tulle especially from mid-November through February when the cabbageworms are active. For more information see my post on Cabbageworms. Slugs will bury themselves in the soil and are hard to find once the lettuce starts growing.
Heirloom lettuce seeds are widely available. Many of the local garden centers have lettuce seedlings available throughout the year.
After some experimenting, I've been able to grow a few lettuce and salad green seeds successfully during the summer months: