Cleaning ponds alone all day gives a person a lot of time to think about life in general, and ponds in particular. I find my mind wandering all over the place sometimes, and have to retrieve it as it gets lost in some corner of itself while thinking about some aspect of pond life and how it relates to the rest of the universe. I had such a moment recently as I worked on a client’s stream. The setting was perfect. It was late morning, I was alone in the yard, the stream sounded just right, and the water felt good on my feet as I went up the stream, removing overgrown plants and fallen leaves, and doing my best to eradicate a plant that I introduced to the pond a couple of years ago, wondering what had happened to my sixth sense of which plants to use and which to avoid.
The pond is made with a flexible liner, covered in stone. I planted it about 5 years ago, when it was new, and have taken care of it since then. There are two streams, each about 25´ long, which converge in a 6´ x 4´ pool, then down about 10´ more of stream and, finally, into the pond, which is about 8´ wide by 12´ long.
The streams have been planted with Iris fulva, Myosotis scorpioides, Ranunculus repens, Ranunculus flammula, Juncus effusus, and so forth. It has been charming as it has developed, and I have been able to move Ajuga, and Adiantum in as the substrate has developed between the stones, all of which gives the entire scene a sense of completely naturalistic randomness, which is important to me. Maintaining it has been a pleasure as I have kept the Bacopa monnieri out of the Anemopsis, and kept the Nasturtium aquaticum, and Echinodorus chordifolius offspring from clogging the stream. It changes with the seasons, and always has something to say to any visitor to the garden in which it sits.
The plant that I was, and have been, struggling to eradicate is Marsh Betony (Stachys palustris). When I acquired this plant, I read the tag on the pot and saw that it said, “fast growing.” I dismissed this as some sort of a marketing ploy, and bought the plant because of the photo of the flower. It produces a spectacular display of purple flowers that rivals those of many other plants. I molly-coddled it through that first winter, having acquired it in November, and made sure that I saved every little piece of it because I was sure that I could use it in my clients’ ponds. Spring came and the plant woke up, grew nicely, and looked pretty. Except for its rough texture, I could see nothing to complain about. The fact that it makes fast growing, heavily branched stolons did not faze me for some reason, and so I moved it to a couple of ponds, including the one described above.
I put the Stachys in one spot on the edge of the pool in which the two streams converge. The first year it did pretty well, giving no hint of the monster that it would become, and was attractive enough to elicit a complement from the homeowner. It went down with winter, as expected, and then came back this spring, seemingly on some sort of a mission to dominate the planet Earth. Before I could say, “Fast-growing my big toe!” it was out of control. It quickly became something like “The Blob,” getting into everything and swallowing any living thing in its path. I have pulled masses of stolons out of folds in the liner, and from under the edge of the liner, from under rocks, and from the surrounding landscape. My plan is to manually eradicate as much of it as possible, then spot spray the rest with an herbicide. I cannot allow this weed to escape on my watch.
All of which brings me to my original point: Which plants should we choose to use in our ponds? And, further, how should we think about their use in our ponds, and, perhaps most importantly, should some species be used at all? The existential questions arise, “What sort of gardener am I?” “Am I the type who will introduce anything, thinking only of what it will look like now, introducing it regardless of its cultural requirements, or the risk that it might pose to the local environment, or am I the type who wants to be more in tune with my environment, and keep only those things that will not overwhelm my yard or, worse, escape cultivation?” Naturally, most of us fall somewhere in the middle.
It is a brave soul here in Southern California that commits to the exclusive use of natives. This is because we suffer a paucity of water-tolerant plants here, being stuck with one or two species of cattails, several grasses or grass-like plants, Anemopsis californicum, Echinodorus berteroi (one of the least attractive member of the genus), a few species of Cyperus, and not much more. It gets very boring very quickly unless we allow exotic species into our collections, which most of us do with glee, since we can grow almost anything here.
Assuming that you have gotten past the existential issues, there are several things to consider when selecting plants to use, including: light exposure, water depth and chemistry, how it will look now and over time, and where it will best serve in one of the two main functions of water plants, they being water conditioning and aesthetics.
There is always a conflict within the hearts of water gardeners, between the desire to have a plant do well, and a need to have them not overwhelm us by their rapid growth. Many times over the years, I have heard people tell me that their pond was doing well, but that the Water Cress or the Parrot’s Feather tried to take over, so they ripped it all out and since then, wouldn’t you know it, the algae have taken over. It never occurred to them that if they merely prune the offending plant, that they can achieve a balance between what the pond needs to stay in balance and what they can tolerate as gardeners.
The use of so-called, “filtering plants,” which are those plants that expose roots to the water (Cress, Hyacinth, Lettuce, Parrot’s Feather, and so forth), is important in keeping water clean because of their role as adjuncts to biological filtration. We all know that beneficial bacteria convert decaying proteins to nitrate, and that plants use that nitrate for their growth, some consuming more than others for that purpose. What many people do not know is that the placement of the plants that we depend upon to filter the water is critical to their ability to do that. Merely sticking a plant into a pond is not a guarantee that it will work for us in the capacity of a filtering agent. It is important to think about where it will serve us best, and what it will need to do its job. For this reason alone, it is a good idea to take plant placement into consideration when planning the layout of the pond. Allowing space for a specimen plant in a 2 gallon pot next to a boulder, or building shelves that can hold trays of soil to get plants off to a good start, or even creating planters along stream sides are things that are sadly lacking in many pond designs.
Because what comes out of the filter is the richest nitrate solution in the entire system, the sooner you can get to it with filtering plants, the better the water quality will be downstream. This is why streams and secondary pools are nice to have in a system. They can be planted so that they are used to strip the water of nearly all of its plant nutrients. In the streams mentioned above, we rarely have any algae of any sort growing in the pond because of all of the plants in the stream. By the time the water gets to the main pond, there is nothing left in it for algae to grow with.
Many plants that are otherwise considered to be “bog plants” can be used as filtering agents if they are allowed to over grow their pots. Once a pickerel plant reaches the edge of its pot, and begins to produce roots into the water, it is just like a big hyacinth, greedily sucking nutrients out of the water. Iris pseudacorus can be used in this way, as well. We need to be mindful of what happens to their seeds, though, because they are very successful in most areas.
One way that I have used Hyacinth and other bog plants in what I call the “rock-filled wonder,” or “quarry” ponds, is to cover the stones on the first shelf with a variety of plants so that they do not grow a lot of algae. Left exposed to the sun, the rocks develop a layer of algae that is difficult to eradicate. Here is southern California, in ponds with black stones in very shallow water, and in the heat of summer, the stones develop a crusty, white layer of calcium from our hard water. Covering them with plants that produce a variety of leaf forms and flower colors is a great way to cover a lot of rocks, and to help the pond integrate more smoothly with the surrounding garden. Using Hyacinth in strategic areas, such as those that are well exposed to the sun in winter, can ensure a nice supply of them as early in the season as the plants will grow in the pond, which makes the pond owner less vulnerable to the vagaries of the local supply. In our area, if the plants are rooted in stones, instead of growing over open water, they will survive most winters pretty well.
When looking for plants for a difficult location, it is useful to think of how a stand of plants might develop naturally. As in the streams mentioned above, I use some species in young systems, not expecting to be able to grow some other plants until the pond has matured. In several instances, I have had large expanses of concrete to hide with plants. Fortunately, there are some species, such as almost any species of Marselea, which can grow almost anywhere and on almost nothing. In the case of Marselea, the rhizomes are tough and wiry, and so, even in death, they make a good framework for debris to get caught, and for other plants to get a foothold in. First the Marselea, or Crassula helmsii, or Bacopa monnieri, or Lippia nodiflora can be planted. Each of these is virtually bullet-proof, and so can be used as primary plantings in difficult areas. Even large species such as Ludwigia repens or L. peploides, can be used in large areas. Once a substrate or framework of plant stems has developed, plants such as Rotala rotundifolia, Myosotis scorpioides, Acorus spp., Irises, Pontederia, Sagittaria spp., or any of a number of creeping or not-too-tall plants can begin to grow. Then, when it is a more solid, higher plants such as Hibiscus spp., Canna varieties, or Cyperus papyrus can be added to give it a fully-planted look that looks as though it has been there for all time. The entire process might take a few seasons to fully develop, but when it does, it is usually worth the wait.
Whichever species we select for our water gardens, we really do need to keep in mind that we are introducing plants to our areas that are almost certainly weeds someplace. We might say to ourselves as we consider a new plant or animal, “Gee, that ought to do well here,” and if we do, we need to remember to be careful with it. It is nice to have a thriving water garden, but we do need to be careful of what we use, and for our own purposes, clever about how we use those plants that we do use.
About the Author
He is also the current President of the Southern California Water Garden Society.