Plants are essential for any pond. They help clean the water and provide food and shelter for fish, wildlife and beneficial insects. The easiest way to grow pond plants is in a pot, set beneath the water on that wonderful ledge you made, or on bricks or blocks stacked on the bottom of the pond. Potted pond plants are much easier to handle than planting them directly into the pond.
There are four main types of pond plants: underwater (or submerged) plants, water lilies, marginal plants and floaters.
Underwater plants including anacharis, cabomba, milfoil and vallisneria (tape grass) are the real workhorses of a pond. These plants, which feed through their delicate, undulating leaves, are the most important plants to grow in your pond. They remove excess nutrients from the water and thus starve out the algae. You can actually keep your pond nice and clear by growing a lot of submerged plants in addition to floaters.
Underwater plants are usually sold in bunches of six or more cuttings each. Since these plants don’t take in the nutrients from the soil, you just pot the bunches up in small pots with coarse sand or rock. Anything to keep the plant submerged will suffice. Lead weights were used in recent years, but have since been discontinued. The recommended plant rate for keeping water clear is one to two bunches per square foot of pond surface. It seems like a lot, but it works!
No pond would be complete without water lilies. Besides being beautiful to look at, these plants have a practical side. They have very large leaves that float on the surface. This floating leaf blocks the sunlight and prevents algae from growing. Water lilies are very easy to grow, and perform best when their pots are set so the crowns (the area where the stem join their tubers) are covered with six to twelve inches of water.
Tropical water lilies can survive outdoor winters only in the frost-free region. Most hardy water lilies can over-winter right in the pond, providing the water lily does NOT freeze solid. That means the pond should be at least two feet deep, or a pond heater is used during the winter months in addition to an aeration system.
To winterize hardy water lilies just cut back the foliage after the first killing frost, then place the pot all the way down to the deepest part of the pond. If you have less than two feet of water in your pond and you don’t heat or aerate the pond, you need to remove the lily in the late fall, trim back its leaves and place the plant in a black plastic garbage bag and place in an area where the temperature stays approximately 50 degrees. Check the lily periodically throughout the winter as it might require some water to keep it moist (it should not be dried-out).
Marginals or bog or edge plants thrive in the water-logged conditions along the margins of a pond. Marginal plants like to be in wet rich soil but they don’t want to be submerged deeply like water lilies. These plants like to have their feet wet, but not too wet. Most marginals should be placed with the top of the pot/container a few inches below the surface of the water or bog. Warm water is the essential key. These are the plants you built that shelf for. Some plants in this category do best at different depths of water, but you should start them all in the shallow water first. As they grow, start experimenting. Some do the best in a shallow stream.
Most marginal plants are grown for their foliage, not their consistent blooms. Some exceptions include the pickerel rush which has spikes of blue flowers, and water cannas (our favorite) which are relatives of the tall canna lilies that grow in well-drained flower beds. Some of the most attractive marginal plants are the tall, spiked ones such as cattails, rushes and sweet flags. This is especially true when they are arranged along the water’s edge to look as a natural habitat.
Tropical marginal plants include Papyrus, Taro, the three foot tall Egyptian Paper Plant, Lobelia and many others. In our region, marginals must be brought indoors before the temperature drops below 40 degrees. Store them in shallow saucers of water in an area that gets bright sunlight all day. You can treat them as house plants, but don’t get concerned about their appearance. Your main goal is to just keep them alive until spring! Hardy marginal plants should survive cold winters right in your pond. We don’t even lower ours to the deep part of the pond. There really are plants that survive winters after being frozen solid!
Floaters are plants you take home from the nursery in plastic water-filled bags just like goldfish. Instead of growing these plants in pots, you float them on your pond. The leaves provide shade while the roots dangle in the water, drawing out excess nutrients and thus helping to prevent algae blooms.
Floaters include water hyacinth, a robust succulent with pretty purple orchid-like flowers, and water lettuce which looks a little like chartreuse cabbage. These are very effective and tend to grow extremely fast during the hot, humid months. They make a delicious addition to any compost pile when they become too numerous.