Let’s grow some lettuce

Lettuce (Lactuca sativa) is probably the most efficient crops to grow hydroponically. It belongs to the Asteraceae daisy group. Known for being a leaf vegetable used in salads and other food items, it is also used for its stem and seeds. Hydroponic lettuce is quite popular as it grows quickly and does not require full sunlight and nutrient solutions for lettuce do not need to be changed during the growing phase.

Just a quick reminder, the Nutrient Film Technique or NFT (sometimes called the Nutrient Flow Technique) is an active hydroponic technique where plants grow in a very shallow channels with a thin stream of water that is recirculated by a pump.

The exposed roots absorb the nutrients from the film of nutrient solution. The channels tend to be slightly sloped so that the water is drained at the end and returns to the main reservoir where the nutrient content, temperature and other factors are controlled.

This system is best suited to grow rapid growing plants like lettuce, pak choi and kale. With the right equipment and guidelines, lettuce can be grown on a commercial scale using the NFT.

The first step is to obtain healthy lettuce seedlings, a reservoir to contain the nutrient solution, an air pump with air stones, water pump, growing channels (usually PVC pipes are used), tubes to deliver water from the pump to the growing trays, net pots and tubing to return water back to the reservoir are required.

A PH meter and electrical conductivity meter should also be obtained.

If using a master-blended hydroponic fertiliser mix, use 2.0 grams of the master-blended fertiliser, 2.0 grams calcium nitrate and 1.0 grams magnesium sulphate to 1 gallon of water.

Lettuce is the only crop that grows with an electronic conductivity (PPM/ parts per million) of between 600 and 800; other crops do well between 1200 and 1400ppm. A pH pf 6-7 is ideal. Ensure also that you take pH and EC readings daily, always use a clean water source in your reservoir and store nutrients in a dry place.

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Follow the steps below for successful NFT hydroponic lettuce:

1. Fill the reservoir with low chlorinated water and add the hydroponic nutrients to the ratio the packaging calls for.
2. Attach the air pump to a tube leading into the reservoir to oxygenate the water. Place the water pump in the reservoir and attach it to a tube that will deliver the water to the channel.
3. When setting up the channel, allow it to be slightly sloped downward toward the reservoir, using a rack for support. Be sure to cut out holes at the top of the growing tray to fit the net pots that will contain the lettuce seedlings.
4. Connect the tube from the pump to the higher end of the channel and attach a tube leading back to tank to the lower end of the channel. This can be done by cutting a small hole at the base on the end of the channel.
5. The next step is to place the net pots in the spaces provided at the top of the channel and sit your lettuce seedlings in them.
6. Ensure that the roots are hanging out of the net pot enough to touch the flowing nutrient solution. Turn on the pumps and in three weeks, the first edible leaves would have grown out. Remove only large leaves, leaving smaller ones to continue the growth process.
7. After about six weeks, fully grown heads of lettuce will be ready for harvest.