As suggested by its name, water lettuce is a floating pond plant with fuzzy rosettes of leaves resembling heads of lettuce. Each leaf has deep ribs and parallel veins, scalloped edges, and no significant stems. Though not showy, the water lettuce plant does produce small white or pale green flowers hidden in the foliage. It blooms from late summer to late fall.
Water lettuce can be used in water gardens, ponds, or containers both indoors and outdoors. This plant’s foliage only grows about 6 inches tall, but its dense root system under the water can grow up to 20 inches deep. It is a very fast grower once mature and is considered an invasive plant in certain areas.
|Botanical Name||Pistia stratiotes|
|Common Name||Water lettuce, water cabbage, Nile cabbage|
|Mature Size||6 in. tall, 10 in. wide|
|Sun Exposure||Full, partial|
|Soil Type||Not applicable|
|Water pH||Acidic, Neutral|
|Bloom Time||Summer, Fall|
|Flower Color||Green, white|
|Hardiness Zones||8-10, USA|
|Toxicity||Toxic to humans and pets|
Water Lettuce Care
To add water lettuce to a pond or water garden, simply spread this floating plant on the water’s surface in the spring. Ideally, choose a spot with no current, as these plants do not grow well when pushed across the water. If there is a current in your water environment, separate the water lettuce from the current by using a floating dam. Items like plastic tubing and suction cups attached to the edges of a tank, a hula hoop, rocks, or fishing line work well for this purpose.
Water lettuce is great for cleaning the water of decomposition byproducts and is often used to keep the water healthy for fish and aquatic life. This plant also reduces algae blooms by blocking sunlight in the water and by using up the nutrients needed for the algae to bloom. It can be grown with most fish, but larger fish, such as koi, cichlids, and goldfish, may nibble on and damage the plants.
Water lettuce originated in Africa in the Nile River, but has spread across the world in aquatic gardens and ponds. If not contained, this plant can be very invasive outside of its native area and can kill native vegetation and fish by choking out sunlight and air exchange on the water’s surface. It can even clog irrigation or drainage systems. Growing water lettuce is prohibited in certain states and countries, so be sure to check your local guidelines before purchasing.
Water lettuce needs full to partial sun exposure. Afternoon shade will help protect water lettuce from intense heat. Water lettuce grown in nurseries is often raised in lower light conditions, so give new plants time to adjust by placing them in low lighting, slowly increasing exposure to more sunlight as the plants become established.
Plants that receive too much sunlight may have yellowing leaves. By contrast, plants that receive less-than-ideal sun exposure may have darker green leaves than is typical.
The roots of this plant are free-floating, so soil is not necessary for healthy growth.
Water conditions are an extremely important part of growing water lettuce, as it is an aquatic, floating plant. Soft to moderately hard water is best. Water lettuce is sensitive to water minerals and can handle no more than 2.5 ppt of salt. It cannot tolerate lime.
Similar to considering soil pH for potted or garden plants, you should also consider the pH of water for the health of water lettuce. This plant prefers pH levels that are neutral or slightly alkaline. Aim for a water pH of 6.5 to 7.
Temperature and Humidity
Water lettuce does best in water temperatures between 70 and 80 degrees Fahrenheit. It's generally recommended for USDA zones 9 to 11.
Because this plant lives in water, it thrives in medium to high humidity levels. Low humidity levels will make growing this plant a challenge as it can dry out the leaves.
In the event that water lettuce leaves begin to turn yellow, a lack of nutrients may be a possible cause. If the water lacks the right levels of nutrients, you may need to supplement with a fertilizer treatment.
There are several different ways to fertilize water lettuce. You can remove the plants and let them sit for a few hours in a tub of liquid fertilizer, add fertilizer straight to the pond or aquarium, or you can add a nutrient booster to the water.
If you choose to add fertilizer or nutrient booster to your pond or tank, factor in the impact it may have on other living things in your aquatic environment, such as other plants or fish. If in doubt, your best bet may be to fertilize water lettuce separately.
Is Water Lettuce Toxic?
Despite its edible-sounding name, water lettuce is toxic to both humans and animals if ingested. It contains calcium oxalate, which can cause burns and kidney damage.
Symptoms of Poisoning
Symptoms of water lettuce poisoning include severe swelling and burning of the lips, tongue, and throat, vomiting, and diarrhea. Immediately contact your doctor or vet if this plant is ingested by children or pets.
Water Lettuce Varieties
- Pistia stratiotes 'Ruffles': As suggested by its name, this variety sports ruffled leaves. It does not grow as large as other varieties, making it a great choice for smaller containers.
- Pistia stratiotes 'Jurassic': This variety produces foliage rosettes that can grow up to 12 inches wide. Though larger than most, it is not a fast grower.
- Pistia stratiotes 'Splash': This variety boasts beautifully variegated leaves and stays small. It is a rare variety and is often hard to find.
The rapid growth and invasive nature of water lettuce require that you prune away runner plants to prevent this vegetation from taking over your pond or water feature. This will usually need to be done on a weekly basis. In addition, if you have an abundance of water lettuce, removing the larger mother plants will help slow the spread.
Propagating Water Lettuce
Since it's such a prolific spreader, propagating water lettuce is simple and easy. Here’s how:
- Using sharp snips, cut the stolon connecting the mother plant to the daughter plant. Daughter plants, also known as runner plants, are vegetation offshoots from the main plant that produce their own root systems.
- Remove the daughter plant and place it in its new environment. These plants will typically thrive, contributing to their invasive nature if propagation is left unchecked.
Starting Water Lettuce from Seed
Starting water lettuce from seed is not common, but it is doable. If you have seeds, here is how to start them:
- Bury the seed lightly in sand.
- Cover the soil and seed with water.
- Keep the soil and seed submerged in water.
- The seed will sprout and eventually fill the container. At this point, it's ready to be transplanted into your aquatic environment.
Overwintering Water Lettuce
Water lettuce cannot tolerate cold temperatures. To overwinter a plant, you can place it in a smaller container of water (such as a fishbowl) and keep it in an area that is above 50 degrees Fahrenheit. Full sun exposure and occasional fertilization may be necessary.
Pistia stratiotes (Nile cabbage, shellflower, water cabbage, water lettuce) | north carolina extension gardener plant toolbox.