Hydroponic Lettuce Nutrients

If you are just starting out with hydroponics gardening, you have recognized that hydroponic growing is good for your health, your bank account, and the environment. Now it’s time to decide which plants to cultivate. One of the most popular plants to grow in a hydroponic system is leafy green vegetables like lettuce. Lettuce is an easy-to-grow vegetable that’s basic to healthy eating and comes in many varieties to try growing yourself. In this article, we will explore the hydroponic lettuce nutrients which are essential for healthy plants.

Hydroponic Lettuce Varieties

Leaf lettuce (lactuca sativa) is the most common type of lettuce grown hydroponically, but similar plants like spinach, arugula, and kale are also easy to grow under the same conditions. Most varieties of lettuce can be grown hydroponically. Select a few varieties that you like best, and you will have a choice of leafy greens for your salad every day.   Some people choose the Tom Thumb variety of lettuce because it grows in small, loose heads that are easy to handle and don’t require a lot of room to grow.  One head makes a salad for two. Bibb lettuce is an easy variety to grow, and Romaine is a decent option but takes a bit more time to mature. Whichever variety you choose, be sure to consider the requirements and tendencies of that particular type, as they can slightly vary.

Here are some popular hydroponic lettuce varieties:

Head lettuce: Boston, Iceberg, New York, Romaine

Looseleaf Lettuce: Buttercrunch Bibb, Simpson, Waldman’s Dark Green

One important factor in choosing which crop to grow is the climate where you live. Lettuce is a cool weather crop. If exposed to temperatures above 70° F., it will bolt. This means it will go into its flowering phase and will no longer be good to eat. Of course, since you will likely grow indoors and under grow lights, that will not be a problem for you.

When harvesting leaf lettuce, pick the outer leaves of the plants and let the inner leaves continue to grow. That way you won’t have to replant as often. Harvesting lettuce with the roots attached extends storage life by 2 to 4 weeks.

Hydroponic System for Lettuce

Hydroponics uses a mixture of water and fertilizer to grow plants (often called a “nutrient solution”). Unlike soil with is dependent on soil composition, weather, and other factors, hydroponics allows the grower to give plants exactly what they want when they want it.  As a result, plants can experience rapid growth, higher yields, and reach their genetic potential more so than field grow crops.  Since lettuce is a fast-growing plant that grows to maturity within 6 weeks, it requires more frequent feeding and maintenance than many other plants.

Most hydroponics gardeners build their own DIY hydroponic system or use a hydroponics system kit. These examples below can be used to grow your hydroponic crops, including lettuce.

Mr. Stacky Smart Farm Vertical Tower

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AeroGrow AeroGarden Harvest

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General Hydroponics Waterfarm Kit

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PowerGrow Systems Bubbler Bucket Kit

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pH Balance for Hydroponic Lettuce

As with swimming pools and spas, checking your water’s pH level daily is the most important step in maintaining a healthy hydroponic system for lettuce. The pH level tells you how acid or alkaline the water is. pH scores range from 0 (most acid) to 14 (most alkaline), with 7 being the neutral point.

Hydroponic plants and soil-grown plants have different optimal pH levels. Be careful not to confuse them. The ideal level for a hydroponics system is 5.5-6.5 (5.8-6.0 is even better). This pH level is acid enough to kill algae and alkaline enough to allow plants to use nutrients efficiently.

If alkalinity is consistently high, “nutrient lockout” can occur. This means that the plants are not absorbing enough nutrients to stay healthy. This will manifest in young foliage paling or turning yellow. Calcium is one of the nutrients that will prevent plants from thriving if the pH level is too high. It can also cause scale on your equipment.

Although most nutrient formulations will result in an ideal pH, plants absorb ions from nutrients at different rates. Therefore, it’s normal for pH levels to fluctuate quite rapidly. Diligence and prompt action are necessary to keep the pH level as steady as possible. Use “pH up” and “pH down” products to keep pH balanced.

In a pinch, you can use baking soda to decrease acidity and lemon juice to increase it. However, commercial products eliminate the need for the guesswork involved in using household products.

General Hydroponics pH Control Kit

  • Works well in all hydroponic environments
  • Kit includes pH Up, pH Down, pH Test Indicator tube
  • 8oz bottle of pH Up (base) which is used to elevate pH
  • 8oz bottle of pH Down (acid) which lowers the pH with its food grade phosphoric acid
  • Fill a test-tube halfway with nutrient, then add a few drops of pH Test Indicator.  The color of the liquid in the vial will indicate the pH level so you can make adjustments accordingly. 
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Hydroponic Lettuce Nutrients

Feed charts (https://generalhydroponics.com/feedcharts/) are available for every type of plant you might want to grow. They will tell you when and how much of each solution to add to your system. You can make your own growing solution to save money, but beginners will probably want to start with a high-quality commercial product to save time and aggravation.


  • Chlorinated water sometimes causes problems with lettuce. Make sure your water source is not heavily chlorinated.
  • Gray mold, a powdery or downy mildew, can plague lettuce. Remove any infected plants immediately.

Before we look at specific homemade and premixed nutrient solutions, let’s explore some of the general characteristics of hydroponic nutrients. Commercial nutrients often come in 2, 3, 4, or more parts so you can change the ratio of the mineral elements for different crops. Make sure you use a solution designed for
hydroponics rather than soil growth.

The essential elements of a hydroponic nutrient are:

✓ Nitrogen (N)
✓ Potassium (K)
✓ Phosphorus (P)
✓ Calcium (Ca)
✓ Magnesium (Mg)
✓ Sulphur (S)
✓ Iron (Fe)
✓ Manganese (Mn)
✓ Copper (Cu)
✓ Zinc (Zn)
✓ Molybdenum (Mo)
✓ Boron (B)
✓ Chlorine (Cl)

Since there is no single recommendation for concentrations of most of these elements, the levels present in your hydroponic nutrient tend to vary among brands. Some formulations also contain some beneficial elements such as Nickel (Ni), Cobalt (Co), Silica (Si) or Selenium (Se) to supplement the essential elements.

Nutrient Problems for Hydroponic Lettuce

Whether you make your own nutrient solution or buy commercial hydroponic lettuce nutrients, problems can arise with deficiencies. Common reasons for this are: (1) the nutrient strength may be too low; (2) the nutrient formula may not be balanced properly; (3) you may unintentionally leave out one of the fertilizer salts or use the wrong fertilizer salt in your mixture. Environmental and internal plant conditions prevent the uptake of certain nutrients. Deficiency symptoms may result.

Nutrient deficiencies usually manifest themselves by wilting and yellowing of leaves. For more specifics, see Identifying Nutrient Deficiency in Plants (http://www.countryfairgarden.com/identifying-nutrient- deficiency-in-plants).

Electrical Current Monitoring for Hydroponic Lettuce

Many growers are still using PPM (Parts Per Million) as a measurement of nutrients to water. This measurement is taken with a TDS (Total Dissolved Solids) meter. There is now an industry movement to standardize the unit of solution measurement to EC (Electrical Conductivity), which is a more accurate
and meaningful way to monitor your nutrients.

A TDS meter measures the EC of the solution, then uses an approximate conversion factor to convert this reading to PPM. The problem is that this conversion factor is never very accurate. As different nutrient solutions have different PPM values, using one conversion figure can be extremely inaccurate.

A plant’s root system responds to is the EC (or osmotic concentration) of the nutrient, so this is what you should measure. There is a wide variety of EC or CF (Conductivity Factor) meters on the market. Growers commonly use the water-resistant, pen-type meters.

Maintaining the correct EC for your particular crop and system is important. Some plants, such as lettuce and other greens, prefer a much lower EC than fruiting crops such as tomatoes. Each crop has its own ideal EC range for optimum growth.

When the EC is too high, plants will soon show evidence of nutrient deficiency. A high EC puts plants under water stress. The plant cells begin to lose water back into the more concentrated nutrient solution surrounding the roots. The first sign of nutrient overuse is plant-wilting. Underuse of nutrients (low EC) will result in plants taking in too much water and looking soft, floppy, and light green.

Since environmental factors affect the ability of plants to absorb nutrients, it is vital that the EC is measured, monitored, and adjusted on a regular basis.

HM Digital EZ Water Quality TDS Tester

  • Highly accurate due to its advanced microprocessor technology.
  • Includes a hold function that saves measurements for recording and convenience.
  • Auto-off function shuts down after 10 minutes of non-use.
  • Easy-to-read large LCD screen.
  • Measurement Range of 0-9990 ppm. 
  • Calibrated with a 342 ppm NaCl solution and includes a TDS chart sticker on the back of the meter for reference.
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Basic Hydroponic Lettuce Nutrients (to Mix)

  • Adjust pH to 6.4 for seedlings or 6.0 for mature plants.
  • Mix 2 teaspoons of 8-15- 36* fertilizer like Food Rising’s Lettuce Formula with 5 gallons of water.
  • Mix 2 teaspoons of calcium nitrate in a small cup of warm water until dissolved. Stir into 5-gal. mixture.
  • Mix 1 teaspoon of magnesium sulfate into a small cup of warm water until dissolved. Stir into 5-gal mixture.
FoodRising Lettuce Formula

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General Hydroponics MaxiGro

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Lettuce Hydroponic Nutrients

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*When you see 3 numbers on fertilizer/plant food, that is an NPK code. N is nitrogen; P is potassium; K is phosphorus. Be sure to follow directions on the product to keep nutrients in the proper proportions. Phosphorus run-off is an environmental hazard, so use it responsibly.

Recommended Hydroponic Lettuce Nutrients (Liquid Solutions)

High levels of potassium, calcium, and magnesium are required to grow lettuce. Some lettuce types are more sensitive to nitrogen than others, so make sure that the nutrients you buy are the right kind for the crop you are growing. Again, follow the nutrient kit directions exactly for best results.

Humboldt Nutrients V405 Verde

  • Use as a leaf-growing catalyst for all your favorite plants
  • Especially good for plants experiencing periods of accelerated growth
  • Strengthens plant structures and enhances plant health
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General Hydroponics Armor Si

  • Suitable for all types of plants and herbs during all stages of growth
  • Improves plant structure and leaf development
  • Enhances growth and increases yield
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FoxFarm FX14011 Grow Big  3-2-6

  • Delivers a full spectrum of nutrients
  • Allows for pH adjustment without nutrient lock up
  • Contains 3-percent nitrogen, 2-percent phosphorus, and 6-percent potassium
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General Hydroponics Flora Combo Set

  • This building block nutrient system includes complete primary, secondary, and micronutrients
  • Better crop quality and enhanced yields
  • pH balanced for easy use 
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Thanks for reading our Hydroponic Lettuce Nutrients article. Feel free to browse through other uPONICS pages, such as Grow Lights for Plants, AeroGarden Reviews, and AeroGarden Marijuana Growing. Best of luck with your grow!