What Is A Pond Plant?
Pond plants are traditionally divided into four categories – marginal plants, oxygenating plants, floating plants, and deep-water plants. There is some overlap between the categories, but they are still useful.
Marginal plants grow around the edges, or margins, of the pond where the water is shallow. They usually have their soil and their crown (their growing point) underwater, and sometimes their lower foliage as well. They are generally placed on shallow planting shelves within the pond, but if you don’t have shelves their pots can be stood on things such as house bricks to raise them up to the correct height. In order to be considered a true marginal pond plant, the variety must be able to tolerate fully waterlogged soil or water over its crown all year. A plant which will tolerate permanently moist soil but will not tolerate water over its crown or foliage, is considered a marsh plant. There is a huge range of marsh plants available, but a much smaller range of true marginal plants. Unfortunately, many attractive marsh plants are sold by unscrupulous sellers as marginal plants, but they will not survive in a pond in the long term.
Marginal plants usually have recommended planting depths - these refer to the depth of water over the crown, or growing point, of the plant (which is about the same thing as the depth of water over the soil level). So a plant with a recommended planting depth of 0 - 4 inches, should be grown anywhere from waterlogged soil (0 inches) up to 4 inches of water over its crown. You can actually grow most marginals in less water than this if you need to, provided that their soil is not allowed to ever completely dry out. However, you should never grow them in deeper water than the recommended maximum.
Good examples of marginal plants would be water irises and marsh marigolds (Caltha species). Most people consider marginal plants as essential to make the pond look natural and attractive, and they also provide cover for all kinds of wildlife.
Oxygenating plants are plants that have all their foliage under the water. They may live on deeper shelves or on the bottom of the pond, or even float suspended in the water – they will grow at any depth where there is light. They are the plants that are sometimes called 'pond weed'; they usually have fine, delicate foliage. A good example would be marestail, Hippuris vulgaris. They are typically fast-growing and can take up food through their leaves as well as their roots, which means that they are good at absorbing excess nutrients from the water. This can help 'starve out' algae and blanketweed and keep water from going green. These plants also provide important habitats for aquatic invertebrates, and spawning sites for amphibians and fish. In addition, because all plants give off oxygen, their submerged vegetation will increase the oxygen levels in the pond during daylight hours. This is where the name comes from, although because the oxygen is lost at night this is actually not an important function. They also give a very natural and pleasing look to the pond, with their luxuriant underwater foliage.
Floating plants, as the name suggest, are any plants that float freely in the water and do not have true roots. Some of these plants are also oxygenators (having fine foliage under the water, such as hornwort, Ceratophyllum species), while others are more like waterlilies (such as frogbit, Hydrocharis morsus-ranae) and have all their foliage on the water surface. Floating plants are quick to put in to the pond because they don't need potting, and quick and easy to remove if they ever need thinning out. They also provide shade for the pond and, because they take up their nutrients directly from the water, they will compete with algae and blanketweed and help keep these in check.
Deep-water aquatic plants are plants that grow on deep shelves or on the bottom of the pond, but unlike oxygenators, most of their foliage is on or above the water surface. This category would include waterlilies (although for convenience, waterlilies are usually listed separately in plant catalogues). Apart from waterlilies, good examples would be Orontium aquaticum, the golden club, or Marsilea species, the floating four-leaf clovers. Apart from their attractive appearance, these plants also provide shade for the pond (which can help with green water) and cover for fish and pond wildife.
When Should I Plant My Pond?
People often contact us asking if it is too early or too late to plant up their pond, but in fact you can plant up your pond at any time of the year. The optimum time for most pond plants is late winter/early spring, as this means that they go in their new pots with fresh soil and food just before they start to grow, so they get the most benefit from this. However, this is preferable, not essential, and it also depends on what qualities you have chosen the plant for. For example, if you have chosen a plant which flowers in very early spring, it may be better to get it planted up and established the previous autumn so that it is not moved and trimmed while the flowers are forming. Or if you are planting a natural pond with a soil bottom, it will be pleasanter to plant, and the plants will establish faster, if you plant in late summer or early autumn when the soil and water are warm.
Floating plants are not usually available in the winter as they disappear down to small buds or shoots on the bottom of the pond and we don't sell them as we think people might be disappointed with how they look. If you want these plants, you will usually have to buy them between April and September.
All of our plants are used to living outside in the British climate, and can be put into your pond at any time of the year.
How Many Plants Do I Need?
This is really up to you and your budget. If you add lots of plants and fill up most of the available space, your pond can look mature and established almost immediately, but you will probably need to start thinning some of them out within about three years. If you space them out more, it will take longer for your pond to look full, but it will cost less. Apart from running out of space, it's not possible to add 'too many' plants. If you are trying to combat green water or blanket weed, add as many plants as you can, in order to really fight the algae.
How Do I Choose?
People often ask us what plants they should have for their pond. If you have fish, then having plenty of oxygenating plants and plants with floating leaves (such as waterlilies or Aponogeton, the water hawthorns) will improve the environment for them and also help significantly to combat algae and green water (which are much more common in fish ponds). In this case, try to have between one-third and two-thirds of the water surface covered with a mixture of oxygenating plants and floating leaves. But if you don’t have fish, then you can really choose whatever plants you like.
To make the pond look pleasing, you might want to consider choosing plants that give different colour flowers and/or flowers at different times of the year (Caltha for yellow flowers in spring, Lythrum for pink flowers in early summer, Pontederia for blue flowers in late summer etc). Foliage is also important – try to choose one or two things that are evergreen, such as Acorus, or Equisetum, so that the pond has some winter interest. For a balanced look, choose both tall slender plants and low bushy plants. If you are trying to hide the edge of the pond, choose plants with creeping stems, such as Menyathes trifoliata (bog bean), Hydrocotyle vulgaris (marsh pennywort), or Mentha aquatica (water mint). Plant heights, flower colour and flowering times are all given on this website on each plant's page.
If you want to use plants to encourage wildlife, the single most important thing is to choose plants from each category so that you have a range of habitats within the pond - plants with underwater foliage, such as oxygenating plants, plants with floating leaves, and marginal plants around the edge. It is also helpful to emphasise British native plants, as they are overall more likely to be useful to our local wildlife.
If you specifically want to encourage dragonflies and damselflies, make sure you have some marginal plants with tall stems that the larvae can crawl up as they emerge from the pond before flying away. If you are interested in butterflies and bees, try to choose plants that are on the RHS 'Perfect For Pollinators' list, such as Lythrum salicaria (loosestrife) or Myosotis (forget-me-nots) - search this site using the keyword "pollinators". Finally, try to place some of your marginal plants and marsh plants around the pond’s edge in such a way that it blends with the vegetation of rest of the garden, to give cover so that small animals can enter or leave the pond without coming out into the open.