How to Grow and Care for Water Lettuce

Water lettuce, or water cabbage, is a floating pond plant with fuzzy rosettes of leaves resembling heads of lettuce, though it’s not edible. Each leaf has deep ribs, scalloped edges, parallel veins, and no significant stems. The plant has small, insignificant pale green or white flowers in between the foliage. It blooms from late summer to late fall.

Water lettuce grows best in freshwater conditions and requires 11 to 12 hours of full sunlight (or dappled light in high heat). It is toxic to people and pets.

Water Lettuce Benefits

Water lettuce is great for cleaning pond water of decomposition byproducts. It is often used to keep water healthy for aquatic life. It reduces algae blooms by blocking sunlight and using the nutrients needed for the algae to bloom.

It can be grown in water gardens providing shelter for small fish, but larger fish, such as koi, cichlids, and goldfish, may nibble on and damage the plants.

Water Lettuce Care

Here are the main care requirements for growing water lettuce:

• Use in contained water gardens, ponds, or pots both indoors and outdoors.
• Needs full to partial sunlight, depending on the heat and exposure level; too much sun can burn its leaves or cause yellowing.
• Provide a neutral to a slightly alkaline or slightly acidic water environment, and ensure it’s not salty or has a noticeable lime content.
• Thrives in water that is 70°F to 80°F.

Light

Water lettuce requires full to partial sun exposure. Afternoon shade is helpful to protect it from heat. In nurseries water lettuce is often grown in lower light conditions, so give any new water lettuce plants time to adjust by placing them in lower light conditions and slowly acclimating them to more sunlight.

Soil

Water lettuce’s roots are free-floating, so soil isn’t necessary.

Water

Good water conditions are key for growing water lettuce. Soft to moderately hard water is best. It’s sensitive to water minerals. It will tolerate no more than 2.5 ppt of salt in the water, and it will not tolerate any lime.

Water lettuce prefers pH levels that are neutral, slightly alkaline, or slightly acidic. Aim for a pH of 6.5 to 7.5.

Temperature and Humidity

Water lettuce thrives in water temperatures between 70°F and 80°F. In USDA zones 9 to 11 it’s grown as a perennial; outside these zones, it’s an annual.

Water lettuce grows best in medium to high humidity levels. The plant’s leaves will dry out in low humidity.

Fertilizer

There are a few ways to fertilize water lettuce. You can add fertilizer or nutrient booster straight to the pond or aquarium, or remove the plants and place them in a tub of liquid fertilizer for a few hours.

If you decide to add fertilizer or nutrient booster to your water, consider how it will impact other living things in the environment. If there’s any doubt, move the water lettuce to its own place for fertilizing.

Water Lettuce Types

There are a few varieties of water lettuce, each with its own distinctive look.

• Pistia stratiotes ‘Ruffles’: This variety of water lettuce has ruffled leaves. It’s a great choice for smaller containers, since it doesn’t get as big as other varieties.
• Pistia stratiotes ‘Jurassic’: Jurassic grows foliage rosettes up to 12 inches wide. It’s larger than most varities of water lettuce, but it doesn’t grow quickly.
• Pistia stratiotes ‘Splash’: This variety stays small, but it has beautifully variegated leaves. It may be difficult to source, as it is a rare variety.

Pruning

Water lettuce grows rapidly and invasively, so regular pruning of runner plants is necessary to keep the plant from taking over the water garden or pond. Pruning weekly will likely be necessary. Removing large mother parents will help to slow the spread.

Propagating Water Lettuce

It’s easy to add water lettuce to a pond or water garden. In the spring, simply spread the plant on the water’s surface. The ideal spot is one with no current, as the plant doesn’t do well in moving water. (If there is a current, you should set up a floating dam with plastic tubing and suction cups or a hula hoop, rocks, or fishing line.

Propagating water lettuce is simple and easy.

1. Identify a daughter or runner plant—a vegetation offshoot coming from a main plant. (It’s safe to remove, since it will grow its own root system later.)
2. Cut the stolon connecting the mother plant to the daughter plant using a pair of sharp and clean snips.
3. Place the daughter plant (the cut plant) in its new location.

How to Grow Water Lettuce from Seed

Though it’s doable to start water lettuce from seed, it’s not common.

1. Bury the seed lightly in sand.
2. Cover the seeds and sand with water.
3. Keep the water level above the sand.
4. Eventually the seed will sprout. Once the container is filled with water lettuce, you can transplant it to its final spot.

Overwintering Water Lettuce

Water lettuce will not tolerate frost or cold temperatures. You can overwinter water lettuce, but it’s inexpensive and grows fast, so it’s easier and more cost-effective to buy it new every year.

To overwinter water lettuce, place it in a small container of water (such as a tupperware container, mixing bowl, or fishbowl). Keep it in an area that says above 50°F. For best results, keep the water close to 70°F. Provide the water lettuce with at least 12 hours of bright light (a greenhouse is an ideal location). Occasional full sun exposure and fertilization can be good.

Common Pests & Plant Diseases

Few pests and diseases are known to bother water lettuce. Koi and goldfish can be a problem and even kill the plants by eating their roots. Insects such as the leaf weevil (Neohydronomous affinis) or leaf moth (Spodoptera pectinicornis) also feed on water lettuce.

Aphids are also known to feed on water lettuce and can be difficult to get rid of once established. They can cause visible damage to the leaves and hinder growth significantly.

Common Problems With Water Lettuce

Water lettuce grows easily on its own but is susceptible to environmental factors, such as sun exposure, lack of nutrients, some insects, temperature, salt levels, and pH.

Yellowing or Browning of Foliage

A lack of nutrients will cause water lettuce to grow poorly and turn yellow. Yellowing progresses to browning. You may need to supplement the water with a fertilizer treatment if it lacks nutrients.

Too much sunlight, like full or direct sun on sweltering days, can cause yellowing leaves and leaf scorch. By contrast, plants that receive less-than-ideal sun exposure may have leaves darker green than is typical.

Wilting Foliage

If your water lettuce plants are failing to thrive or drying, temperatures may be too cold. Incoming winter season or frost will cause wilting, stunted growth and death if the conditions persist. Although it is hardy and sometimes hard to get rid of when unwanted, water lettuce is meant for warm climates.