It's time to think beyond the traditional in-ground flower plant. For a new twist on the backyard flower garden, turn your attention to floating aquatic plants like the water hyacinth (Eichhornia crassipes), an aquatic perennial flower in U.S. Department of Agriculture plant hardiness zones 9 through 11 that you can also treat as a summer annual. Showy lavender or purple blossoms add a flash of color to your pond or container water garden. With the proper care, your water hyacinth will flourish.
Water hyacinth can be invasive within its hardiness zones. If you live in USDA zones 9 through 11, do not plant water hyacinth and try an alternative aquatic plant. Regardless of where you live, do not grow this plant in ponds or waterways that connect to storm drains, streams or other natural waterways, or in places where wildlife may pick up the plant and carry it to new areas. Completely enclosed container water gardens may be the safest bet, but don't grow the plant if it's problematic in your area. Check with your local county extension office to see if there are regulations in your area concerning water hyacinth.
Location and Spacing
If you grow too many floating plants, they won't allow enough sunlight to penetrate the water. In contrast, if you have too few floating plants, the excessive sun can provoke algae blooms and other problems in your pond or container. For the best results, use one water hyacinth or any other floating plant for every 5 square feet of water surface.
Water hyacinth requires full sun. That's a minimum of six hours of direct sun every day. If your water garden does not get enough sun, move the water garden to a sunnier spot if it's a portable container garden. If your water garden cannot be moved, consider growing a different floating plant.
If you want to keep your water hyacinth floating in a specific part of your water garden, anchor it in place. Tie a nylon string around one of the water hyacinth's stems and tie the other end of the string around a rock or brick placed at the bottom of your water garden.
Water Top Ups
Water hyacinth do not require regular water changes, but you must top up the water garden whenever it loses water through evaporation. Check the level of your pond or container garden every couple of days in summer. Add water if you notice the water level being lower than the highest water mark on the pond or container's sides.
In the wild, decaying organic matter, dead insects and other organic debris help to fertilize aquatic plants. In your pond, occasional fertilization helps to supplement water nutrient levels and keep the water hyacinth looking its best.
Marginal pond plants and other aquatic plants that grow in submerged pots do best with fertilizer tablets pushed into their soil. In contrast, floating aquatic plants, like water hyacinth, require liquid fertilizer added to the water.
Follow the label guidelines on the specific pond or water garden fertilizer product you use, as instructions vary by product. For example, when using a 0-0-3 fertilizer for ponds, add 1/2 tablespoon for every 15 gallons of water twice monthly. Make sure you use a fertilizer labeled for use in ponds.
Pests and Diseases
The water hyacinth has no serious disease problems or insect problems. A few general cultural practices can ensure that pests and diseases never become an issue:
- Do not overcrowd the water hyacinths. Poor air circulation increases the risks of diseases and insect problems.
- If you're growing water hyacinths outside of their USDA plant zones, wait to set them outdoors until daytime temperatures are a minimum of 70 degrees Fahrenheit and evening temperatures are a minimum of 50 F.
- Keep the plants in a sunny spot.
- Never introduce dying or injured plants into your water garden.
If you notice aphids and other soft-bodied insect pests, crushing them with your fingers or a gloved hand can keep insect populations at levels too low to cause problems. Or, make an oil spray. This kills pests without endangering water quality or the aquatic plants. Mix 2 parts of vegetable oil with 8 parts of water, plus 1 teaspoon of liquid dish soap. Mix thoroughly and spray it directly onto pests. For the best results, apply the spray in the evening and rinse the water hyacinths with fresh water the next morning. Repeat once every 10 days until pest problems subside.
Overwintering Water Hyacinth
Water hyacinths thrive in warm weather and die if exposed to cold winters. Unless you live within their preferred USDA plant zones, grow them as annuals or overwinter them indoors. If you choose to overwinter water hyacinths indoors, bring them indoors before the first frost date in your region. Put the plants in a tub and set the tub near a window where it can receive at least six hours of sun per day.