One of the most popular plants to grow in your hydroponic system, especially for beginners, is microgreens, herbs, leafy green vegetables, and Hydroponic Lettuce. Lettuce grows rapidly in minimal space with high yields and low maintenance. Lettuce is a hardy, cool-weather crop and can be planted year-round in your indoor hydroponic system.
Common Types of Lettuce Grown Hydroponically
Crisphead / Iceberg – Light, Round, tightly packed crunchy leaves (common restaurant salads)
Romaine – Dark, long, crisp leaves (Caesar salads)
Butterhead / Bibb – Dark, Loose packed, that resembles a flower. (very popular hydroponically grown lettuce)
Loose Leaf / Gourmet– Light or reddish, long, Curly leaves loose-packed along a visible stalk.
For most lettuce grown in indoor hydroponic systems, the following guide will work. There will be variations in each category depends on the specific type of lettuce and the method and type of design of your system.
- Temperature – Day 68-75 degrees and about 60-65 at Night. They can tolerate higher temperatures without bolting and lower temperatures for short periods.
- Humidity – Tolerant to high humidity
- Light – 11-14 hours at lower light levels. May need to supplement with white or blue light for red types of lettuce
Nutrient and PH levels
- Electrical Conductivity (EC) – This will change over the growing cycle of the lettuce. Most varieties start around .5-.7 for freshly transplanted sprouts and increase feeding levels over the life cycle to end up around 1.5 just before harvest
- Nitrogen (N), Phosphorus (P), and Potassium (K) Nutrient Balance concentration– There is no standard. N8-P15-K36 works very well for us; however, we have seen success with a 9-3-6 liquid-based nutrient.
- pH – We found most lettuce varieties do well with a pH value of 5.8- 6 (Acid enough to kill algae and alkaline enough to allow plants to use nutrients efficiently)
Methods, Media and more
- Best system methods – Kratky Method, Nutrient Film Technique (NFT), Deep Water Culture (DWC), Ebb & Flow or Flood and Drain Method. NFT being most popular for small commercial growers and hobbyists and DWC systems for large commercial growers and Aquaponic systems.
- Harvest Period – Periodically as soon as 3 weeks, one leaf at a time or 45-55 days for a whole head depending on the type of lettuce. Romaine and some darker leaf lettuce can take up to 85 days
- Growing media – Stone wool and phenolic or other foam are most common. Cut up pool noodles are often used in some DIY hydroponic systems
Hydroponically grown lettuce is not only one of the fastest and easiest vegetables to grow, but it is also more sustainable than other growing solutions. Re-circulating the nutrient solution saves water, reduces nutrient runoff and minimizes evaporation. The best home hobby lettuce grow tips we have seen so far include:
- Start germination process with paper towel method or 2 Seedlings per stone wool starter cubes.
- Germinate in darkness for 3 days then transfer to low light location
- Optimum germination results at nutrient solution temperatures of 60-68°F otherwise your seeds will go into thermal dormancy when exposed to higher temperatures.
- Transfer to NFT trays after about 1.5-2 weeks ( when roots start to grow out the bottom of the starter cubes)
- NFT Method with reservoir aeration and 5 min on 20 min off repeat timer
- Bibb, butterhead, Boston, and loose-leaf lettuce types
- full spectrum LED lighting with infrared set to 12 hours on for the first 2 weeks of growth then raised to 14 hours
- 8 pH
- .8-1.5 EC
- 8-15-36 NPK Nutrient concentration
- Periodic harvesting within 3 weeks. Full heads within 6 weeks