Basic Guide On Growing Lettuce In Hydroponic System

In recent years, lettuce has suffered a bad reputation – some foodies and environmentalists claim that too much water and fertilizer are being used to grow a crop with very low nutrient density. Even so, lettuce contains Calcium, Magnesium, Phosphorus, Vitamin A, Vitamin C, Vitamin K, Folate, Iron, Potassium, and Manganese. Additionally, lettuce has dietary fiber and can help you stay hydrated because it is high in water

Among the most popular hydroponic crops, lettuce (Lactuca sativa) is of course the most popular. Due to its growing requirements and production rate, lettuce is ideal to grow in greenhouses, controlled environments, and with great success in even beginners’ gardens. Hydroponics reduces evaporation by saving water significantly, making it a great way to grow a healthy, sustainable lettuce crop.

There are a number of reasons why hydroponic lettuce gardening is so popular both for commercial and home growers:

#1. It can be grown as a year-round crop in controlled environments: A full head of the plant requires only 45-85 days to produce its first edible leaves and about 3 weeks to get to that stage of growth.

#2. It doesn’t require full sun and grows well even in low light and temperatures: As it is primarily a leafy vegetable and will never reach a flowering phase, nutrient solutions are straightforward and don’t need to be changed during the growing season.

#3. It can be harvested one leaf at a time (which extends the harvesting season) or as a whole head, depending on your needs and ambitions.

Hydroponic Lettuce Growing Requirements

Although lettuces are typically considered non-demanding crops for hydroponic cultivation, they require special care.

#1. Temperature

In general, lettuces love cooler temperatures. High temperatures are favored for flowering/bolting, which is an unpleasant process that causes the leaves to turn unpleasantly bitter. Daytime temperatures should be between 68 and 75° F (20-23°C), never exceeding 77° F (25°C) due to the rapid bolting process in temperatures higher than that. If you’re growing lettuce in a completely controlled environment, consider adjusting the nighttime temperature to 60 to 65°F (15-18°C), though even lower temperatures may be easily tolerated in the short term.

#2. Light Duration

Lettuce does not have high lighting requirements. Ten to fourteen hours of moderate light, or even low light, is sufficient. On the contrary, growing in full sun can cause lettuce leaves to turn bitter and the plant to bolt much faster. Generally speaking, butterhead lettuce has an optimal DLI requirement of 17.1 molm–2d–1, although most leafy greens and lettuces can tolerate a seasonal reduction to 12 molm–2d–1. In late fall, winter, and early spring, in northern latitudes, some additional lighting may be required in order to achieve this goal.

If the lighting is too low, another pigment called anthocyanin stops being produced. If you are planning on growing red cultivars, consider supplemental lighting or blue light coming from diodes.

#3. Growing Media

In hydroponic lettuce grown in NFT or DWC systems, the solid growing medium (in the form of a substrate) is designed to allow seedlings to sprout and provides basic root support as the plants grow. Lettuce seedlings may be started on a wide range of substrates. Stone wool and phenolic foam are probably the most commonly used substrates for starting seedlings. A number of varieties of coco coir and peat moss have been stabilized with chemical binder or mesh wrap. The real growing medium is the water nutrient solution in which the plants grow.

Lettuce requires a nutrient solution that will maximize yields in the vegetative phase, still preventing it from moving into the flowering phase. The solution should have a ratio high in nitrogen, phosphorus, and potassium, but not too high in potassium. The micronutrients are also important here; for lettuce varieties that tend to suffer from tip burn, make sure there is always enough calcium in the solution. The concentration of dissolved oxygen should only be maintained at around 8 ppm. Although some lettuce varieties are tolerant to low oxygen levels, maintaining the solution well aerated will certainly promote healthy growth.

#4. Grow Period

Leafy green lettuce is a short-term and fast-growing crop. The time a lettuce head takes to become ready for harvest will vary according to the variety. It can be 45-55 days for butterhead lettuce, while romaine and other lettuces with tighter heads can take up to 80-85 days. The production of lettuce is highest in the spring, during the frost period, and prior to the summer heat. In a controlled indoor environment, lettuces can be grown year-round. 

The Most Commonly Grown Lettuce Varieties

Good news for all lettuce lovers in the world is that hydroponic systems allow you to grow any of the popular varieties of lettuce. While Iceberg is the lettuce queen in conventional fields, hydroponic lettuce is a bit different and more diverse when compared to conventional lettuce. Generally speaking, hydroponic plants have a preference for loose heads, although tight head varieties such as Iceberg are still able to be grown with some adjustments.

It is one of the great advantages of the loose lettuce varieties for the home gardener – unlike the types with cabbage-like heads, the leaves of the loose-leaf lettuces can be picked separately, so they will grow and re-grow individually through the season. This significantly extends the harvest and is suitable for those growing lettuce for their own needs.

#1. Romaine Lettuce

Romaine lettuce is one of the most common types of lettuce due to its distinctly crunchy texture and stronger flavor. There are different cultivars of romaine lettuce available; some produce more closed heads, while others produce a more open head.

#2. Butterhead Lettuce

Butterhead lettuce is probably one of the most widely grown lettuce in hydroponics, and it is also one of the most widely grown conventionally outside of the U.S. family. Butterhead lettuce has two main subtypes, which mainly differ in shape.

Boston lettuce has a round, rose-shaped head; Bibb lettuce, or “limestone”, has a cup-shaped head. Both lettuces have a distinctive buttery texture that leaves a slight sweetness in the mouth; otherwise, the flavor is mild.  It has also been observed that both varieties produce compact plants that can be harvested as a whole head or leaf by leaf.

#3. Loose-Leaf Lettuce

This type of lettuce consists of numerous varieties with one feature in common: they form loose leaves on the stem, rather than forming a head. Their taste is mild, and crispness is somewhere between butterhead and romaine.

There are many cultivars on the market that offer both green and red leaves and are either smooth or ruffled. The “Oak leaf” cultivar is unique in that it produces tiny heads of leaves resembling overgrown floppy oak leaves. You should take into account that there are many different cultivars for each type of lettuce, with colors ranging from vibrant green to deep red and varying in flavor intensity.

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