Lettuce thrive off the moist nutrient rich environment that aquaponics provides. They are also able to be grown in a range of different aquaponic growing conditions like deep water culture, channel or flood and drain, see here. This makes lettuce a versatile and relatively inexpensive choice for the aquaponic gardener. We have a kit set up at the front door of the house and stagger the planting so there is always a fresh supply of lettuce on hand.
Spoonshaped lettuce like cos or romaine will do well in the warmer months and are the most nutritious of the lot. Lettuce like the butterhead, or boston are a softer lettuce and are better suited to colder growing conditions and tight head lettuces like crisphead, or iceberg, fit somewhere in between. My personal favourite is the cos, but growing lettuce like red oak and butter crunch will provide for a colourful salad mix.
When planting out your lettuce seedlings it is important that you allow enough space between plants. This will prevent them from overcrowding and being prone to bottom rot or disease. It is also important to wash all of the soil media from the roots of your lettuce seedlings before planting them out to prevent disease and to ensure adequate aeration of the roots.
Lettuce are best harvested early in the morning or picked and thrown straight into a salad at night. Normally the leaves will fill with water over night and are subsequently much plumper in the morning. The outer leaves of loose-leaf lettuce can be picked at any stage, allowing the inner leaves to keep producing.
Things to watch out for
Depending on how densely your fish are stocked you may end up having issues with your lettuce being overfed with nitrogen. Although your lettuce will mature quickly the leaves may be poorly structured and prone to wilting. Some leaves may even appear burnt around the edges, this is termed tipburn. Tipburn is the result of an inadequate supply of calcium to the lettuce plant and is best corrected by supplementing calcium into the system in the form of calcium carbonate (garden lime) or eggshells. More info around using additives in your aquaponics system can be found here.
Lettuce are also prone to bolting over the summer months meaning that they will shoot to seed and turn bitter rather quickly. The best thing to do is to choose a variety that will cope better in hot conditions and keep your kit in a shady area to slow their growth and reduce bolting, see here.