Marginal plants are simply the aquatic plants found growing around the edges, or margins, of your water garden. To create a natural-looking pond, a good selection of marginal plants is very important. There are hundreds of varieties to choose from and they come in all shapes, sizes, textures, and flower colors.
Other than just adding beauty and naturalization, marginal plants also serve many other purposes in the water garden. They add valuable filtration to the pond and they remove elements that would otherwise feed algae. They attract and provide cover for wildlife, and you can also select from among many different hardy or tropical varieties.
In an ecosystem pond, marginal plants are generally placed directly into the gravel. This lets them thrive naturally and filter the water more effectively. Certain plants like thalia, bulrush, and reeds can be problematic and may even damage the pond liner. You should either avoid planting them altogether, or plant them in an aquatic pot, surrounding the pots with rocks and gravel to maintain the natural look of the pond.
Streams are another great place for marginal plants. Again, they provide valuable filtration as the water flows past their roots. They also soak up additional nutrients, minimizing algae problems. Just picture the last time you saw a stream in nature and all the wonderful plants growing in the water along its edges. That’s the look you want to create.
Start by selecting the proper plant for the water depth, sun exposure, and location. Water depth is an important consideration when it comes to choosing aquatic plants. More specifically, the concern is with how much water a plant will tolerate above its crown. For this reason, most marginals are planted on the first shelf of the pond. Select plants of different heights, foliage types, and flower colors to create a pleasing mix.
After selecting the plants, it’s time to place them in the pond. Start off by washing away most of the soil from around the root system. You don’t want to disturb the root system of the plant, so be careful and avoid removing too much. Once the soil has been removed from the plant, push the gravel back and place it in the pond, filling the gravel back in around the root system.
The same process can be used for planting in a stream – carefully selecting aquatic plants that like or tolerate the stream’s moving water. Not all marginal plants can thrive in moving water.
If the plant you decide to use is overly aggressive, you should consider leaving it in a pot to help contain the spread of the roots. Remember, most aquatic plants prefer width over depth in their respective growing areas so give them plenty of room to spread out. Many marginals are shallow-rooted, therefore depth is less of a factor than surface area.
To plant, fill the hole-less aquatic pot with 2-3” of heavy topsoil, placing the fertilizer in the bottom of the pot. Unlike the marginals you planted in the gravel, you will need to fertilize these plants as they are not as effective at drawing nutrients from the pond because their roots are contained by the pot.
Finish filling in around the plant’s roots with heavy topsoil. Then fill the pot to within one inch of the top, firmly pack the soil, and cover it with a ½ to one-inch layer of gravel. Remember, when you’re done, the gravel level should be about even with the previous soil level.
Taking care of marginal plants in an ecosystem pond is fairly simple. Remove any dead, discolored, or excess plant material as needed. Marginal plants (unless they are in pots) do not need to be fertilized, as they will flourish from the nutrients in the pond.
For winter care, simply cut the plants back to two or three inches above the water level of the pond. In the spring, remove all dead plant material. And remember, the growth of plants that are directly in the gravel is not restricted – they will need to be thinned so they don’t engulf more of the pond than originally planned.
The flowering waterlily may be the apple of your water gardening eye, but marginal plants play a crucial role in the function, maintainability, and beauty of a properly-conceived water garden. Without marginal plants, the water garden will look out of place and unnatural. They provide many textures, colors, and blooms that soften the edges and help blend the pond into the surrounding landscape. So when you’re in the planning stages of a water garden project, don’t forget the marginals because they’re simply part of Mother Nature’s recipe … and we all know better than to argue with her.