My Water Lettuce Pond Plants Are Dying

Cold Temperatures

• Water lettuce will not thrive in pond water temperatures below 40 degrees Fahrenheit. Oftentimes a pond owner will not realize that temperatures are falling this low during the overnight hours. Place a thermometer in your pond and check it three to four hours after sunset. If your pond temperature is near or below 40 degrees, consider installing a pond warmer to keep your pond temperature above this temperature and your water lettuce thriving.

Water Quality

• Water lettuce absorbs a lot of its nutrients from the pond water. If your pond water quality is sufficiently poor, you may see a dieback in your water lettuce. Consider getting your pond water tested, and ensuring that you have a filtration system running at least 12 hours per day will help keep the algae level down. Algae blooms can deplete dissolved oxygen in your pond, as well as use up nutrients your water lettuce needs to survive.

Sunlight

• Water lettuce is a tropical and subtropical aquatic plant. It needs several hours of direct sunlight per day to thrive in most zones. If your pond is receiving less than this amount, you may want to consider cycling your water lettuce to and from an external container that receives more sunlight, moving plants from your pond to the container as they begin to wilt.

Fish

• If your pond contains fish, they may be chewing the roots of the water lettuce faster than the plants can regrow themselves. Lift up your pond lettuce and see if the root clumps are substantially reduced in size. A full-grown water lettuce plant should have trailing roots as long as 10 inches in length. If they are much shorter than this, below 5 inches, your fish are probably eating the roots out from under your plants. Koi are especially fond of water lettuce roots. Provide more food for your fish, or consider using an external tank to allow water lettuce to recover before returning to the pond.