How to Grow Hydroponic Lettuce

Lettuce, the incredibly healthy and versatile vegetable, comes in four major varieties: butterhead, crisphead, romaine, and loose-leaf. You can use it as a top in juicy burgers, salads or play around with your creativity if you are a foodie.

As versatile it is, lettuce has numerous antioxidants that protect your body from unstable molecules or free radicals and is one of the easiest to grow hydroponically. It has high yields, and low requirements, ideal for controlled grow environments.

You can grow lettuce in controlled grow environments all-year-round, even as a beginner with no gardening background, and the good thing is you don't have to wait for long.

It only takes between 45 and 85 days to harvest a fully grown lettuce head.

Unlike other plants, the vegetable does not require full sun exposure and can grow even in low-temperature conditions.

Typically, lettuce should not get to the flowering stage, and there is no need to change the nutrient solution over its growth stages.

Benefits of Growing Lettuce Hydroponically

Before we can jump right in on how to grow hydroponic lettuce, it's probably best to explore the benefits. Don't you think?

So what are the advantages of growing lettuce hydroponically?

Some environmentalists have lately been giving lettuce a bad rap by claiming that a lot of fertilizer and water goes into its growth, despite its low nutrient density. But this claim is debatable.

Well, lettuce has reasonable amounts of nutrients, and the argument of low nutrients density does not hold water. Lettuce comes packed with vitamin A, Vitamin K, Vitamin C, Vitamins B1, B2, B6, phosphorus, magnesium, calcium, iron, folate, potassium and manganese. It's a full house.

This other group argues hydroponically grown lettuce is not as nutritious as its soil-grown counterparts. But this is baseless as well.

Hydroponic lettuce can have as many nutrients as outdoor soil lettuce, depending on the nutrient solution.

What's more, the veggie has a high water content to keep you hydrated and is an excellent dietary fiber source.

Growing the crunchy and delicious lettuce in a hydroponic system is convenient and saves water that may be lost through evaporation and into the ground. This pretty much takes care of the argument that lettuce uses a lot of water.

But most importantly, growing lettuce in a hydroponic system is a walk in the park, and therefore the perfect method for anyone looking to start growing their own vegetables.

Hydroponics is an excellent choice for folks with no space for an outdoor garden or those interested in growing vegetables all year round. It is a far cleaner and more efficient method than the old-fashioned container gardening that some people still use today. Plus, the vegetables grown hydroponically tend to taste better and are bigger than the outdoor garden varieties.

If growing lettuce to sell, healthier lettuce heads attract all the right attention to put some money in your pocket quicker, which is a good thing.

All the lettuce varieties will perform well in a controlled hydroponics system. However, the loose-leaf is most preferred by home gardeners. You can pick the leaves of the loose leaf individually to allow the plant to regrow throughout the season. This suits the needs of home growers quite well.

The Different Types of Lettuce

Lettuce is touted as one of the easiest vegetables you can grow, and it's not hard to see why. Well, there are so many varieties, and it's almost sure you know someone that grows lettuce in their backyard.

●     Loose-leaf Lettuce

The loose leaf lettuce group's main characteristics are that they don't form heads, thus the name. This variety combines a bit of crispness with a mild and delicate taste.

There are varying loose leaf cultivars with both red and green leaves.

●     Butterhead Lettuce

This variety is one of the most hydroponically grown and has two main subtypes: Boston lettuce and bibb lettuce. Boston lettuce has a rose flower head shape, while the bibb lettuce carries a smaller, more cup-like head. Both compact plants can harvest single leafs or as an entire head.

These butterhead subvarieties have a buttery texture and a unique sweet taste, and mild flavor.

●     Romaine Lettuce

Most people recognize this lettuce variety because it is one of the Caesar salads' components. It has a stronger taste and is quite crispy.

Romaine lettuce has different cultivars where some have more open heads, and others have a bit tighter heads.

Hydroponic Lettuce Growing Requirements

Lettuce is far from demanding crops, but a little care goes a long way to ensure a bountiful harvest. Here are some of the requirements:

  • Higher temperatures are undesirable as they tend to make the lettuce bitter. The average day temps should be between 68 and 75° F (20 and 23°C). The veggies will benefit from lower nighttime temps.
  • The ideal medium pH is between 5.5 and 6.0.
  • The most appropriate electrical conductivity value is 1.4 mS/cm
  • Lettuce is not quite light-hungry and around ten hours of low to moderate light is enough. The precise daily light integral (DLI) is 17.1 mol·m–2·d–1.

Hydroponic Lettuce Growing Medium

Hydroponic lettuce growing uses a substrate form as a medium for sprouting and basic root support. There is a wide range of substrates, and they include phenolic foam, stone wool, and stabilized peat moss, or coconut noir.

Water nutrient solution, with high nitrogen, some phosphorus, and a bit of potassium NPK ratio, is the real medium that supports the crops' growth. Ensure there is enough calcium in the solution, and keep it well aerated at around eight ppm oxygen. We recommend using an air pump for this. Check out our air pumps here

Calcium deficiency is a significant problem for hydroponically grown lettuce, and it can cause tip burn. This discolors the leaves and drives the development of slime, reducing its shelf life and making it unsellable. To ensure plants get enough calcium in a hydroponics system, we strongly recommending using a Cal/Mag nutrient. This will help keep leaves bright green instead of yellow. 

  • You can either use the classic hydroponics, Deep Water Culture (DWC), or the Nutrient-Film Technique (NFT) method. DWC or the pond culture circulates large volumes of water to prevent significant EC, pH, nutrient composition, and temperature fluctuations.
  • The NFT has shallow channels that continually circulate nutrients in a thin film. The slightly sloped channels drain the water back to the reservoir, where nutrients, pH, and other factors are controlled.
  • Ebb and Flow flood the root zone with a nutrient solution and then drains it back to the reservoir. It is also the flood and drain system.

For more information on which technique to go with, our previous blog, The Value of Hydroponic Farming, will give you a further break down of each system. 

Getting Started

We've mentioned that hydroponic lettuce is not tricky, but there is a learning curve, even though not steep, if you want to make significant strides. You will need to spend some time and energy managing the hydroponic system to help the lettuce reach its full potential. But it is one of the most fulfilling exercises.

  • The first step is to sow your seeds in a growing medium seed starter. Rockwool cubes are ideal starters if you intend to grow hydroponic lettuce.
  • Spun basalt fibers in Rockwool will generally have a higher pH. Make sure to bring it down to the right level before commencing.
  • The lettuce seed that will germinate properly is between 75 to 80%. Every seed should be in its own cube, but this may vary depending on the lettuce variety. You are free to grow more and thin out depending on development - the survival of the fittest.
  • If there's no growth within two weeks, consider restarting. Slow growth is a sign that all is not well in lettuce paradise.
  • Transplant the little plant once it attains around five mature leaves. The baby roots should also have roots sticking out of the growing medium bottom.
  • There are various signs to inform you the lettuce plants are healthy and doing well. Look out for stunted growth, necrosis, and discoloration. Make necessary changes if you notice something is not right to save your plants' lives.

Harvesting Lettuce

Your lettuce should be ready within three weeks, and you can harvest individual leaves after this period. Harvest the bigger outer leaves and leave the inner ones to continue growing.

You can also wait for about five to six weeks for the whole head to develop. Note that harvesting the fully developed head is different from harvesting only the leaves. Typically, leave the head intact and instead cut the roots off.

Place the crown in a cup of water or wrap it with a damp paper towel to extend its shelf life.

Final Word

If you are looking to acquire some skills on how to grow hydroponic lettuce or looking for a ready-made system, SuperCloset is a good bang for your buck. The premade hydroponics system is easy to use and supports your lettuce plants for instant gratification and success. Of course, you can always make your own hydroponic system, but why go through all the trouble of trial and error?  Happy gardening!

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