A great looking pond always has a full complement of plants that bring it to life and encourage wildlife to flourish. Here's Dan Everton's guide to choosing the correct plants for your pond.
A pond wouldn't be complete without plants. They are part of the eco system, a natural method of filtration, capturing nitrate, phosphates and other nasties, absorbing carbon dioxide and then oxygenating the water.
They also provide cover, nesting areas and food for fish and other pond life while helping to restrict algae growth. Not least of all, they look good, an attractive addition to the pond and garden as a whole.
What plants you choose depends on such factors as how large the pond is, how deep, how much light it gets etc. If you have an extensive pond clearly you can invest in a range of large and small plants to create an aquatic landscape.
If the pond is not so large, you'll want a smaller selection of plants that won't dominate the water. Don't over plant and choose carefully, noting the potential height and spread of any plant as you would normal garden plants. A clue might be in the name, there's lots of 'dwarf' and 'pygmy' plant varieties out there.
Plants fall into several categories: Bog or Marginal, Deep Water, Floating and Oxygenators.
When your pond was constructed, shelves should have been included, about 6ins - 15ins below the water surface, while the main body of water is preferably anything from 1½ - 4ft deep. A marshy area created next to the pond is an added bonus.
Bog and Marginal Plants
Plants for the wet marshy portion include Cotton Grass, Creeping Jenny, Forget-Me-Not, Primula and the dainty pink Cuckoo Flower. These are planted directly in the soil but, to restrict their spread, you may want to plant them in a container. Also choose the species carefully as some prefer a waterlogged but not submerged soil while others can tolerate less moisture.
Marginals, that either grow tall or 'raft' over the surface are planted in baskets and will occupy the shelves. The depth i.e. how far the water is above the top of the basket is important and depends on the species. For example, Sweet Scented or Flowering Rushes will be 3 – 5ins, Bog Arum 2 – 4ins and Marsh Marigold 0 – 3ins. Ensure that the taller marginals, rushes and irises are in large baskets that provide a secure anchorage.
The most popular Deep Water Plant is the water lily with which everyone is familiar. The leaves float on the surface while anchored to the bottom of the pond. Even if you have a small pond there might be a water lily for you, Nymphaea candida perhaps, that has a planting depth of only about 12 ins and spreads to approximately 2ft. Pygmy Water Lilies are even smaller and can be planted in water to a depth of only six inches.
Be careful when you put water lilies into the pond, by placing bricks under the basket they can be lowered in stages, so the leaves aren't totally submerged.
Floating Plants and Oxygenators
True Floating Plants like the invasive Water Hyacinth and the Water Lettuce (note these are not frost hardy but the native Water Soldier will survive the winter by dropping into the water) live on the water surface developing a root system that, together with the shade that the plant provides, is effective in restricting algae growth. By lowering the water temperature, the shade will also provide a cool retreat for fish.
Oxygenating Plants such as Hornwort or Spiked Milfoil float in the water feeding on decaying organic matter, cleaning the water and releasing oxygen into it. A good supply of oxygen is essential for pond life and plants to thrive, but make sure they don't take over the pond as this can be harmful to fish and avoid invasive species such as Parrot's Feather altogether.
When it comes to planting, for marginal and deep water plants you will need a basket if they are bought bare rooted. Some container grown plants will also need potting on. The baskets are usually black plastic with lattice sides, and you can choose between round, square or kidney shaped.
Inside the basket, hessian squares are placed to prevent the soil from being washed away and these will also restrict the plant from becoming too large and invasive. Synthetic hessian, that claims to be longer lasting and finer than the traditional material, is also available.
As a growing medium you must always use specialist aquatic compost, usually loam based with added grit to give weight and stability to pond plant containers. A layer of gravel on top of the compost is always a good idea to make sure it stays in the basket. Then just lower the basket into position to the correct depth.