Water Plants

One of the highlights of a water feature is the anticipation of watching that first water lily bloom open up in spring. The excitement of seeing nature stretch its wings after a cold winter is perhaps best seen in the water garden.

Plants love to grow, and we love to watch them, but often things can go wrong. Here are a few tips to help.

Water plants are just like any other plant; they need nutrients, water and light to survive. Water and light are easy to provide, but the nutrients can be more difficult. Fertilizing the aquatic vegetation is accomplished several different ways. Most commonly fertilizer tablets are pushed into the soil surrounding the plant, and are taken up by the roots. Some fertilizers are added directly to the water. The main difference in the liquid and tablet fertilizers is which plants they help. The fertilizer tabs are great for the plants whose roots are in the soil (lilies, bog plants), the liquid helps plants with roots suspended in the water (hyacinth, parrot feather).

Probably the biggest mistake people make is not fertilizing enough and often enough. In the height of the growing season water lilies need two fertilizer tabs per gallon of soil every two weeks to bloom profusely. Any of the commercially available fertilizers are fine. In the Southeast, the weather warms up enough in early May for things to really get going. Much before then the water is too cold for the plants to grow well.

The first plant to bloom is usually the iris, followed by many types of lilies. Lotus and tropical lilies won’t become active until late May, and often into June, when the water temperature is above seventy degrees. Water hyacinth and lettuce are also tropical and like warmer temperatures too. Parrots feather, another floating plant, can start growing well around sixty degrees, especially if it is potted. If lilies and lotus are fertilized well, and regularly, you can expect them to be blooming continuously from late May well into October. While the lilies and lotus re-bloom, many marginal or bog plants bloom only once, and are finished.

In late October, right after the first frost, you will notice the plants wilting and looking unhappy. Now is the time to remove all the dead or dying plant leaves before they fall off and decay in the pond. Virtually all plants just need to be cut back to the soil level, and placed in water deep enough to keep them from freezing, at least ten inches. Irises are a notable exception, because they are actually evergreen. If you were to cut them back, they will grow back in early spring; but you won’t get as many blooms, so usually it is better thin the iris out, and place in deeper water for the winter.

While you are winterizing the plants, it is tempting to re-pot the extra growth now while you are in the pond. This is perfectly fine, but if you can plan ahead the best time to re-pot is in early fall, a good month before first frost, in our area this is usually early September. This will give the re-potted plant time to grow into its new home and become more established for the next season. You will be rewarded with lots of blooms and vigorous growth. Many people use a potting medium specifically designed for aquatic plants. This aquatic soil is an excellent product, but it is quite costly, especially for multiple plants. An affordable alternative would be 2/3 screened top soil (no twigs or sticks) and 1/3 sand. This mix provides plenty of substance for the roots, while still being easy for the roots to spread into. Most plants just need to be planted at the crown (where the roots start to grow), in the center of the pot. Lilies and iris have a tuber, and new growth occurs at the growing end of the tuber; consequently they spread outward in only one direction. If we plant the tuber in the middle of the pot, it will quickly be at the edge, and need to be re-potted again. If we place the tuber at the side of the pot, with the growing end facing the other side of the pot, it will grow across the pot (through the center) to the opposite edge. This will give you a little more time before the plant needs re-potting again.

To finish the re-potting process, a few handfuls of large gravel on the surface of the soil helps to keep the soil in the pot, and not in your pond. This also keeps the fish from digging up the plants, with large Koi, use larger gravel (up to three inches) to keep the soil in the pots. If you keep them wet, and fertilize your plants regularly you should be rewarded with lush growth
and lots of blooms.

Fortunately, aquatic plants aren’t plagued with many problems. Here are some quick things to remember: The less light you have the less blooms you will get. The plant will still grow and be happy, but it just won’t bloom very much. Both koi and goldfish love to eat plants. Koi especially can make quick work of any exposed vegetation. Aphids are the only insect pests to worry about, they like plants right at the water surface (lily pads, hyacinth, lettuce). Many controls are available, just read the cautions first to be sure it is safe for fish (diluted malathion 1: 10 works well). Lilies do best in 18-24” of water, and marginal (edge) plants prefer a maximum depth of six inches above the soil.