Iceberg Lettuce, which is also sometimes called crisphead lettuce, is among the most popular varieties of lettuce in the United States. It can be easy to grow, but it is temperamental enough that simple mistakes can turn what could have been a great harvest into spoiled, rotted leaves and seeds. However, if you give iceberg lettuce the conditions it likes to grow in, it can give you a harvest of delicious fresh greens straight from your garden to your kitchen.
If iceberg lettuce matures too late, it can lead to your crop spoiling in your garden from the heat. Because iceberg lettuce takes a relatively long time to mature — over 70 days, in some cases — this can be a serious problem, so anything you can do to let yourself plant earlier is a great idea. Unfortunately, iceberg lettuce is also vulnerable to frost, which prevents you from planting too early.
Because of these two things, give yourself a head start and plant your iceberg lettuce inside, in a seedling tray, before the last frost in early spring. Plant your lettuce seeds about 1/4 inch deep, and use a few seeds in each space. Stagger your plantings by 1 or 2 weeks. This way, your plants will mature at different times, ensuring that you have a steady supply of lettuce when you harvest, rather than a large amount all at once that you will not be able to use while it is fresh.
Iceberg lettuce needs cool temperatures to germinate. Room temperature will work just fine. Water your iceberg lettuce often enough to keep it moist, but rarely enough to prevent the soil from becoming waterlogged. Seedlings should sprout after about 1 week.
Once you are absolutely sure that the soil in your garden is not going to freeze, it is time to plant your seedlings. Iceberg lettuce has shallow roots, and is vulnerable to frost. Give your iceberg lettuce plenty of water, but in small amounts so the soil does not get soaked, since this can allow harmful fungus to grow.
Try your best to keep your iceberg lettuce cool as well, as it will grow best at lower temperatures. On hot days, setting up a tarp to produce shade is a very good idea. Another thing that can help moderate the temperature of your lettuce is mulching. Use an organic mulch, not black plastic, since black plastic will raise your soil temperatures — the opposite of your goal. Peat moss can cause a similar problem. Instead, use something like dead leaves, grass clippings, or hay. Mulching will also help control weed growth, which can be a serious problem for iceberg lettuce due to its shallow roots.
Iceberg lettuce responds well to fertilizer with nitrogen in it. However, as always, overusing fertilizer is more likely to harm your plants than underusing it, so be careful.
After about 3 months, your iceberg lettuce should be mature. Plan accordingly, even before you plant your iceberg lettuce seeds. Allow yourself sufficient time to harvest your lettuce, or it will go to waste.