Hydroponic lettuce is started in trays with any potting medium. Once the starts have four true leaves, they are transplanted into net pots filled with hydroponic medium. The net pots just act as containers to hold the medium in place. They fit into holes in a hydroponic table, and the bottoms get immersed in water.
Your growth medium can be just about anything. It must allow the roots to penetrate through it. Ideally it should have a neutral PH and remain porous when immersed into water. Popular mediums include:
- Rock Wool
- Grow Rock
- Coco Fiber
A reservoir beneath the system holds most of the water. The water is pumped from the reservoir through a shallow table beneath your net pots where the roots can access it. From there it goes back into the reservoir and is recycled through the system. An airstone or fishtank pump should be used to move water and add oxygen in the form of bubbles. Oxygenated water is necessary for plant growth.
The reservoir could be an old fish tank or plastic storage container. Avoid metal containers as they tend to oxidize and release unwanted substances into the system.
Organic nutrients for hydroponic systems are available at garden stores. Because your plant roots will be sitting in the solution, it’s highly important that the balance of nutrients to water is stable.
Lettuce plants require certain nutrients and are notable consumers of potassium, calcium, and magnesium. They can be sensitive to nitrogen-heavy solutions. Find a nutrient solution that is formulated for lettuce or similar vegetables and follow the instructions for adding it to the reservoir.
Hydroponics typically happens indoors. Most systems require artificial supplemental lighting. Many vegetables will need powerful lights like halides in order to get what they need. Lettuce plants are less picky and only need some inexpensive fluorescents.
Typically hydroponic gardeners will give lettuce about 18 hours of light per day. This long-day growth cycle will grow them quickly and to their full potential. Butter lettuce plants can form full heads within a month.
PH and Temperature
Check the PH of your water solution daily to make sure it is between 5.5 and 6.5. Your roots are living in this solution so it is important not to let the PH fluctuate too drastically.
For lettuce, a temperature range between 55-75° Fahrenheit (12.7-25° C) is best. Any hotter than this can cause lettuce plants to bolt. With the environmental factors under control, your lettuces will grow faster than ever.