Wildlife ponds 3: planting and aftercare
Plant life
To make your pond as much like a natural pond as possible, you should put a layer of soil on top of the liner and plant into this. The drawback is that aquatic plants will spread very rapidly and, unless cleared frequently, will soon choke the pond. To limit management work, a good practical compromise is to use planting containers in the pond, supplemented by planting pockets around the edge. You will lose some wildlife value by doing this, but many creatures, including frogs, toads, newts and some dragonflies, are quite happy in these conditions.
For planting, use rotted turves or, failing that, ordinary garden soil that has not been treated with any chemicals. Spread gravel on top of the soil, especially in planting containers, because this helps to keep it where you want it.
You need both submerged and marginal plants in any pool – see pond plants for suggestions. As a rule of thumb you should have enough plants to cover about half the surface of the pond, to avoid problems with excessive algal growth. Water lilies come in a wide range of colours and sizes and are valuable for this purpose as well as being decorative, but native species are too vigorous for any but large ponds. Plant at any time in the growing season, i.e. April to September.
Expect your pond to take some time to settle down after planting. It is normal for some algae to appear early in the year and then disperse, but if this problem persists or duckweed spreads rapidly, it is a sign of high nutrient levels in the pond and you should plan to desilt it the following autumn.
Animal life
It is worth acquiring water snails from a pond supplier because they help to keep the pond clean but otherwise, unless your garden is very remote from any other pond or waterway, you can safely leave nature to supply all the residents you need. Alternatively, seed it with a bucket of water from a friend's established pond, but beware of bringing in invasive plants like duckweed at the same time.
Do not introduce ornamental fish if you want frogs and dragonflies, because they eat their eggs and larvae. It is also best not to collect frogspawn because of the risk of spreading disease.
Maintenance
Keep an eye on the water level throughout the summer and top up if necessary, using rain water if possible. Do not be too fussy about this though, because it is quite normal for pond water levels to fall in summer and many plants and animals are adapted to it. Many marginal plants, for example, grow as happily in wet soil as they do in shallow water.
Oxygenating and floating plants spread vigorously, and often root into the silt that accumulates on the base of the pool. It is best to thin regularly every autumn rather than going in for wholesale clearance which may seriously disturb the balance of the pond.
When leaves fall in the autumn, try to keep them out of the pool and rake out those that do get in. At the same time, cut back some of the emergent plants above the water level. This helps to keep nutrient levels down, so that plants do not grow too vigorously. Never clear more than half of the vegetation so that you leave enough eggs and larvae behind for next year. Pile the material on the bank for a day or two to let mobile creatures escape back to safety before you barrow it away for composting.
Every five years, or sooner if you have problems with algal growth or rampant duckweed, remove the accumulated silt from about half of the pond and, again, pile it on the bank for a while before removal.