Yellowing Leaves on Aquatic Plants

Types of Aquatic Plants

• A number of attractive aquatic plants are available for your water garden. Water lilies are picturesque in both northern and tropical regions. Leaves and cheerful flowers in shades of pink, blue, yellow and white float on the surface. Water lilies, along with the lotus and yellow floating heart, grow roots in soil while stems and foliage float at the surface. Aquatic plants such as water hyacinth and water lettuce have both foliage and roots that float. University of Vermont Extension states that many floating plants are invasive, especially in tropical regions; be sure not to release your aquatic plants into bodies of water.

Aphid Damage

• Aphids often cause yellowing foliage on aquatic plants. These tiny 1/8-inch insects drink the sap from young leaves, resulting in curling, wilting or yellowing. Damage typically occurs in late spring and continues through summer. Black aphids are a pest of water lily and have black bodies shaped like a pear. These and other kinds of aphids spend the winter on plum and cherry trees and also find passage to a water garden through infested plants. If you spot signs of aphids on your aquatic plants, remove sickly leaves or hose aphids off leaves into the pond as a snack for the fish.

Fungal Diseases

• Aquatic plants under stress are susceptible to fungal diseases. Low oxygen, poor water circulation, plant crowding and temperature extremes are a few stresses that indirectly lead to yellowing foliage. According to Colorado State University, symptoms of root rot on water hyacinth appear as wilting and yellowing leaves and black, limp roots. If you observe these symptoms, remove the afflicted plant from the water garden. Another fungal disease related to plant stress is Helminthosporium leaf spot. On the aquatic plant, papyrus, this fungus causes red spots on plant parts and yellow foliage. Control this fungus by ensuring plants are not root bound and increasing air circulation.

Nutrient-Poor Environment

• Aquatic plants require fertilizer just like your plants above water. Yellow leaves are a sign that plants are hungry for nitrogen, phosphorus or other nutrients. Give your aquatic plants a boost by adding liquid fertilizer to the water or pushing a tablet of fertilizer into the soil. When potting water lilies and lotus, University of Illinois Extension suggests applying four ounces of fertilizer per cubic feet of soil; be sure to feed your water plants every month during the growing season.