The good news with growing lettuce hydroponically is that there really isn't any bad news. In fact, it's the easiest vegetable to grow using hydroponic methods.
Choose the Right Variety
Bibb lettuce grows very rapidly as do the leaf lettuce varieties. Romaine also does well although it takes just a bit longer to reach maturity. Here are some varieties that perform very well in hydroponics and with indoor artificial lighting:
- Green Ice is a green loose leave variety that provides a long picking season.
- Red Fire is a deep red, loose leaf type that is suitable for both cool and warm climates.
- Tango grows very well in cooler conditions only.
- Royal Oak Leaf is a heat tolerant darker green type of lettuce that does well in hydroponic growing systems.
Start the Lettuce
It's best to start lettuce in rockwool starter plugs. Before planting you'll need to soak the rockwool plugs in a conditioning solution with a pH of about 5.5. This lowers the pH of the plugs to about 6.2.
After conditioning the rockwool, the excess solution is drained off and the lettuce seed is placed into each plug.
Cover the tray of starter plugs with a plastic humidity dome and place near a window or under a cool fluorescent light. In a few days it will germinate.
Once the roots begin to poke out through the bottom of the plugs they may be transplanted into your hydroponic growing medium.
You have a few different options when it comes to your growing medium, including neutral pH media such as perlite, vermiculite, hydroton, gravel, sand, cocofiber, etc. Our preferences are:
Hydroton is the trademarked name for clay balls that are kiln dried. These clay balls offer the perfect air to water retention ratio for optimal plant root growth.
While more expensive to buy, these clay balls can be reused many times over. Before reusing Hydroton, all plant matter should be washed. The Hydroton pellets should also be soaked in water and hydrogen peroxide.
The typical ratio is one table spoon of hydrogen peroxide per gallon. Other brand names for this product include: HydroCorn and Plant!t.
Growstones are another type of growing medium. They are engineered to provide a highly effective balance between air and water content.
They hold 3 times more water and 12% more air than Hydroton type mediums and work well as a growing media for vegetables and herbs. Manufactured using up to 98% recycled glass bottles
Coconut fiber: For hydroponic use we recommend only the course, shredded coconut fibers as these will allow for good downward water movement in the towers. Remember though that coco fiber may contain high levels of sea salt so rinse it very well prior to use.
Don’t forget to add nutrients! Every plant grown hydroponically needs the food it’s not getting from the soil. We've had good success with PureBlend Pro Grow.
Lettuce is a cool weather crop, which means long days and hot summer temperatures can cause the crop to "bolt," or go to flower and turn bitter. So make sure you are growing your lettuce in a cool area.
Regularly check your nutrient solutions pH as well as total salt concentration level.
A pH of around 6 is a good target for lettuce. As far as total salt ppm, we recommend keeping it between 700 and 1000 ppm for lettuce.
Metal halide lights provide an excellent full spectrum light for lettuce. They are rich in the blue end light spectrum, which is important healthy lettuce growth.
T5 fluorescent grow lights are less expensive and also a good light source for lettuce. We suggest a minimum of 12 hours/day during the late fall and winter months for plants grown indoors.
Harvest & Storage
Hydroponic lettuce is generally harvested with the roots attached. Leaving the roots intact provides a longer post-harvest storage life; plants can stay fresh for 2 to 4 weeks under the proper storage conditions (near freezing temperatures and high humidity). Tip: Pick the outer leaves as your lettuce grows and you'll end up with an extended harvest of crisp, fresh lettuce. As you cut the outer leaves away, the inner leaves quickly grow to take their place.