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How to Grow Lettuce in Home Aquaponics Systems

There are a huge variety of plants that can be grown in aquaponics systems, from species that produce food to those that produce flowers and pretty petals, the choice is almost endless. One family of plant that does well in all types of aquaponics is leafy greens; and one of the most popular, regularly consumed leafy greens is lettuce. In addition to these plants being a great ingredient for many dishes, they are also associated with several health benefits such as a reduced risk of stroke, heart disease and some cancers including lung, bladder, gastric and colorectal cancer. 

Choosing to grow lettuce in aquaponics provides several benefits over most other plants. It’s easy to grow and maintain, whilst also being rather resilient to changes in temperatures. These factors make lettuce a perfect choice for this effective aquaculture-based growing  method.

lettuce aquaponics

Best Species of Lettuce for Aquaponics

There are over 100 different species of lettuce, many are edible but some aren’t. Fortunately since the plant is one of the most popular for the aquaponics method, there is a general consensus on what lettuce is best for aquaponics.

The best types of lettuce to grow in aquaponics includes:

Loose-leaf lettuce: One of the most common and easiest to grow using aquaponics. It is highly tolerant to changes in temperature and grows very fast. It’s also great to eat, has a mild sweetish flavor and is a great source of vitamin A.

Butterhead aka Bibb Lettuce: Another common leafy green, Butterhead is soft, mild, and slightly sweet. It grows fast and has a higher market value than other lettuce; making it ideal for aquaponics.

Romaine: One of the most durable lettuce to grow. It typically grows taller, thicker, and extremely tolerant to change in water temperature.

Lettuce As a Companion Plant

Lettuce is commonly used in companionship with other plants, and although it may not have pest or disease preventing properties it does grow fine with several other species of plant including carrots, beetroot, parsnip and radish.

Avoid growing lettuce with plants from the same ‘Brassica oleracea’ family, this includes cabbage, broccoli, cauliflower, kale, and Brussels Sprouts, since the roots of these plants secret a substance that can prevent lettuce seeds from germinating.

Best Type of Aquaponics to Grow Lettuce

Growing lettuce in aquaponics is easy to start, monitor and maintain, it’s also very resilient to changes in temperature. Its versatility does extend to the types of aquaponics techniques that can be used to grow the plant.

However, whilst it is in theory, possible to grow lettuce with any aquaponics technique, you’ll no doubt see better results by employing NFT or floating raft systems/deep water culture (DWC) aquaponics.

Growing Lettuce in Aquaponics Pros and Cons

Lettuce is a family of plants that boast all the right characteristics to thrive in aquaponics. Being so well suited to the technique provides a number of benefits when compared with other plants. However, as you might expect, together with these advantages there are a couple of disadvantages you should know about, these include:

Advantages of Aquaponics Lettuce

  • Extremely popular edible plant
  • Easy maintenance
  • Easy monitoring
  • Tolerant to changes in water temperature
  • Low nutrient requirements
  • Grows quick in nature; two to three times quicker in aquaponics 
  • Edible; tasty, used in many dishes
  • Essential for healthy diet, provides numerous health benefits

Disadvantages of Aquaponics Lettuce

  • Most varieties have mid to low market value
  • Grow so fast time between replanting may be inconvenient
  • If roots develop disease lettuce is typically not worth saving; whole crop will be lost
how to grow aquaponics lettuce

Nutrient Levels

If you’re new to aquaponics and/or have little knowledge regarding the chemicals and chemical processes that take place within the system, it’s likely you’ll have come across the term limiting macronutrient and micronutrient.

This may not initially raise any red flags; it seems to make sense that some nutrients would “limit” the process that occur in the system. Naturally, you read on, only to come across statements that claim:

“N is one of the most limiting macronutrient and micronutrients”

As well as;

“K (Potassium), Ca (Calcium), and Fe (Iron) are the most limiting macronutrient and micronutrients”

This immediately triggers alarm bells since we know that N is nitrogen, and we know that sufficient nitrogen levels are essential for a functioning system. So what exactly is the confusion?

The truth behind these statements simply comes down to context. In fact, in scientific terms ALL nutrients can be limiting, it depends on the conditions and whether or not the levels of these nutrients are beneficial to the ecosystem. For example, in some cases nitrogen is considered limiting when levels are either to high or too low, since both can cause uncontrolled plant growth.

Optimal Levels For Growing Lettuce in Aquaponics

pH level: The most suitable pH range for lettuce is between 5.8 and 6.2, however the plant is extremely sturdy and can handle levels a measure or two outside this range. This allows the plant to survive in the slightly more alkaline environment typical of aquaponics, between 6.8-7.2.

Water and Air: Ideal temperatures for aquaponics water and air is between 68°- 86°F (20-30°C). Lettuce thrives between 70° to 74° (21-23°C) and is therefore a perfect plant for this aquatic method.

Plant Spacing: Space your lettuce at least 7 inches apart. This space will encourage maximum growth, prevent overcrowding, and ensure each plant receives enough light. This spacing will also depend on the lettuce variety you’re planning to grow.

Recommended Fish: The most popular aquaponics fish all work well in systems where lettuce is grown. Edible aquaponics fish ideal for matching with lettuce include tilapia, trout, bass, and sunfish; some non-edible species include koi, carp, and goldfish.

Time to Grow and Harvest Lettuce in Aquaponics

Lettuce is one of the fastest growing vegetables in the world, and this speeds ups twofold when aquaponics is involved. Traditional gardens take between 7-8 weeks from planting seeds to harvest; whereas aquaponics can reduce this time to around 30 days for most lettuce, and up to 45-60 days for others.

Depending on the species of lettuce, growing periods will look something like this:

  • Starting seedlings: 10-15 days
  • Transplanting seedlings: 3-5 days
  • Grow period: 2 weeks/14 days or more

Fastest Varieties of Lettuce

  • Coastline summer crisp lettuce – 30 days
  • Flashy butter oak lettuce – 30 days
  • Ithaca iceberg lettuce – 30 days
  • New red fire loose-leaf lettuce – 30 days
  • Ice green loose-leaf lettuce – 30 days
  • Lau’s pointed leaf romaine lettuce – 30 days
  • Summer bibb butterhead lettuce – 30 days

Slower Varieties of Lettuce

  • Corn salad mache lettuce – 50 days
  • Parris Island romaine lettuce – 50 days
  • Tennis ball bibb lettuce – 55 days
  • Tom Thumb butterhead lettuce – 55 days
  • Frisee endive lettuce – 65 days
  • Celtuce lettuce – 75 days

Getting Started Growing Lettuce in Aquaponics

The Cycling Process and Nitrification

The cycling process is essential in balancing the system. It is carried out by beneficial bacteria in the system, known as nitrifying bacteria, which ensures that enough nitrates are converted for the plants to thrive. It’s possible to begin this cycling process with or without fish, it’s also possible to reduce the time it takes to complete a full cycling by adding more nitrifying bacteria.

The cycling timeframe depends mainly on water temperature, but typically takes between 4-6 weeks, during which time you’ll need to monitor levels daily and adjust them when necessary. The presence of nitrates will indicate cycling is taking place. Then once ammonia and nitrite levels drop below 0.5 ppm with cycling is considered complete.

Start Lettuce Seedlings for Aquaponics

  • Place 3 to 5 seeds in starter medium such as Rockwool cubes or peat pellets
  • Place the medium in a starting tray
  • Water the seeds adequately, place the tray in a dark place
  • Subsequent watering should be done once a day, for 14 days, using a fine spray mist
  • Seeds will sprout after 10-15 days; they are ready to transfer when sufficient height is reached, or when two or three true leaves appear from the stem.
  • NOTE: We can’t stress enough the importance of cycling aquaponics systems prior to placing fish and plants. It’s a step that cannot be skipped nor corners cut, so be sure to follow guidelines and only commence growing once the cycle is complete.

Transplanting Seedlings for Lettuce Aquaponics

The transplanting process involves moving your potted seedlings from the starting tray into your system. This is typically done after around 3 weeks, once the seedlings have reached adequate maturity. This process should is straightforward; the only additional step requires the grower to let the seedlings acclimatize to the new surroundings better.

To do this:

  • Systems set up in colder climates will require exposure to the colder temperature and direct sunlight for at least 3 to 5 days
  • Conversely, systems operating in warmer climates will require the seedlings to be placed under shade for 2-3 days, in warmer temperatures closer to the internal operating temp of the air and water.

Lettuce Aquaponics Maintenance

Once the seedlings have been successfully transplanted into the aquaponics system all that’s required from that point until harvest is to monitor levels and keep the system in check. Maintenance will mainly consist of monitoring the system and making slight adjustments when necessary. Monitoring can be performed using test strips, or dedicated devices designed to such as pH sensors and dissolved oxygen sensors.

Important factors to monitor will include:

  • pH Levels: check the pH every week. The ideal for lettuce in an aquaponics system is pH is 6.8, and should not go above 7.
  • Water Temperature: Water temp affects all aspects of the system, and therefore should be kept stable, 70° to 74° (21-23°C) is the ideal temp range for lettuce.
    • Be sure to use de-chlorinated water when replacing water in the system.
  • Ammonia: Essential precursor for the conversion of nitrites and nitrates
  • Nitrites and Nitrates: The nutrients required for the plants growth
  • Pest Infestation: Check for signs of pests daily. Should you spot any immediately remove the plants, it’s not advisable to use pesticides, so if removable is not sufficient, try using beneficial insects to eat the unwanted pests. Adding companion plants is another way you can avoid pest infestations in your aquaponics garden (chives and mints are perfect companion plants for lettuce).

Harvesting Lettuce Aquaponics

There are two main ways you can harvest your lettuce crop: 

Cut and Come Again: when the plant reaches a size you deem acceptable for consumption (doesn’t have to be full maturity), you can start cutting/harvesting the outer leaves (popular with loose leaf varieties and romaine). As the plant grows, the leaves you cut off will eventually be replaced.

Whole Head: when the plant reaches maturity or a size you deem acceptable for consumption, you can cut at the base of the plant and harvest the entire head of lettuce (popular with iceberg, bib, and romaine lettuce).

lettuce aquaponics plants

In Conclusion Lettuce Aquaponics

When it comes to the health of your aquaponics system, maintaining a stable environment is crucial for the survival of plants and fish in the ecosystem. To do so growers must perfect the art of balancing levels, a task largely governed by the species of plants and fish you choose. Some are easier to grow than others, and each has different requirements to keep operating levels within safe ranges.

Lettuce is an ideal plant for aquaponics because it is easy simple grow, maintain and monitor, it also has low nutritional requirements and is extremely tolerant to changes in pH and temperature. Although lettuce doesn’t have the highest market value, it remains an extremely popular leafy vegetable that’s still in high demand; which does at least help to increase the overall value.

So if you’re looking for a plant that’s simple, easy to grow, and packed with a number of benefits over other plants, Lettuce is an ideal choice for both beginners and expert aquaponics growers.

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