Marginal plants are perhaps the most versatile plant group in the water garden. They add beauty, color, texture, and valuable filtration, and are called marginals because they’re typically planted around the edges, or “margins,” of the pond.
Marginal plants typically thrive in wet soil or standing water that covers the crown of the plant anywhere from two to six inches. Some species even thrive in water more than two feet deep. Marginal plants come in an overwhelming assortment of genera, providing you with many shapes, textures, colors, and sizes. Choose a miniature sweet flag that’s only a few inches tall, or a tropical thalia whose flowers are borne 10 feet above the surface of the water. The most common and readily available varieties of marginal plants include iris, sweet flag, pickerel plant, canna, thalia, bulrush, and cattail, to name just a few.
The Elegant Iris
Aquatic irises, a popular sight in many water gardens, are among the first plants to bloom in the spring. They comprise such a large and diverse group that they are sometimes treated separately. This category includes, but is not limited to Louisiana iris, Japanese iris, Siberian iris, and native aquatic iris such as blue flag. The Asiatic/European yellow iris has become naturalized in North America and is often found in ponds. There are literally hundreds, if not thousands, of cultivated and natural hybrids within each group.
Beautification and Naturalization
With so many different shapes, sizes, and colors, choosing marginals could be overwhelming. On the flip side, it’s not hard finding a marginal plant to fit the needs of your pond.
Besides adding beauty and naturalization, marginal plants add valuable filtration to your pond. They consume a tremendous amount of nutrients that would otherwise feed algae. We know that ponds are great for attracting wildlife, and marginal plants can help in that effort by giving frogs and toads shelter and protection from weather and predators. Marginal plantings also provide shelter for many types of birds who drink or bathe in your pond, and the sweet nectar of many of the flowering plants can attract butterflies and hummingbirds. Butterfly weed, cannas, and lobelia are especially good for this.
Tropical and Hardy
Marginal plants are available in both hardy and tropical species. A combination of tropical and hardy should be planted in your pond in the same way you mix annuals and perennials in your flower beds. Hardy plants reliably re-appear to greet you each season, getting bigger, and giving your pond a mature look with each year of growth. Tropicals only last one season, but they’ll add an exotic touch to your pondscape.
If you prefer not to spend money on plants that won’t return each season, keep in mind that tropicals can be over-wintered as houseplants. Simply pot them in plastic or ceramic sealed containers without drainage holes. Fill the container with soil, and top with gravel. Give the plant a sunny window and keep it saturated with water and it will survive indoors. You can incorporate a grow light if you think it’s not getting enough direct sunlight.
Maintaining Marginal Plants
Taking care of marginal plants is fairly simple. Remove any dead, discolored, or excess plant material as needed. Marginal plants (unless they’re in pots) generally do not need to be fertilized, as they will flourish from the nutrients in the pond.
For winter care, cut the plants back and, in the spring, remove any remaining dead plant material to make room for the new, bright green shoots that emerge.
Remember, the growth of marginal plants that are directly planted in the gravel of your pond is not restricted. Be careful to avoid overly aggressive species (like water celery) or they could take over your pond. No matter which marginal plants you choose, you’ll need to do a little thinning from time to time to keep them in check.
A Final Note
The flowering waterlily might be the highlight of your pond, or the lotus your pride and joy, but marginal plants play a crucial role in the function, maintainability, and beauty of a properly conceived water garden. Without them, the pond could look a bit barren and unnatural.
Marginals provide texture, color, and blooms that soften the nearby rocks, and help transition the pond into its surrounding landscape. It’s fun to experiment with different plants over the years, so have fun choosing and placing plants in your water garden. Play with colors, textures, and heights of marginal plants and you’ll soon feel like an artist working with a watery canvas.