Water is vitally important to the wildlife garden. Amphibians such as frogs and toads breed in ponds, water snails and the larvae of insects such as dragonflies and damselflies live in ponds, diving beetles and pond skaters rely on the pond habitat. Insects such as bees, wasps and hoverflies need shallow water to drink, and birds require water for drinking and bathing. Winter bathing for is essential to fluff out their plumage and protect them from the winter cold.
When it comes to designing and building a pond, the bigger the better – 4 square metres is generally the minimum size needed to create a balanced environment. One area of the pond needs to be very shallow, with very shallow edges to allow wildlife to get in and out of the water and to drink from the side safely. Planting shelves can be designed in for marginal plants. It should also have a depth of at least 60cm at some point in the centre. This will benefit a range of wildlife and allow you to grow a range of plants.
An open, sunny place without overhanging trees is best for the siting of a pond. I would always specify a heavy duty butyl liner, which is the toughest kind of liner and can last up to 40 – 50 years. Polythene liners need protection from sunlight – ultra-violet rays can make any exposed liner crack. Also, polythene liners use solvents in their creation which can leach into the water and therefore are not good for wildlife. I would use a geotextile layer to cushion the liner, and if necessary put in a drainage pipe or gravel drain underneath to allow the ground water to be drained off and not accumulate under the liner creating a ‘hippo’ which can push the liner up. ‘Hippos’ can also be created by decaying organic matter underneath the liner, so make sure there are no leaves in the hole before placing the liner in. You also have to ensure there are no stones or sharp shards which might puncture the liner. The best option to be sure of creating a pond that will suit your situation and last, is to have it professionally designed and built.
When it comes to planting, use low nutrient clay to plant into, not topsoil which is too full of nutrients. Oxygenators are crucial to creating the balance needed in the pool and oxygen needed by wildlife living in the water. They grow densely and provide egg laying and nursery sites and cover for many aquatic creatures. Use native plants such as Ceratophyllum demersum or Ceratophyllum submersum (Hornwort) and avoid Canadian pondweed (Elodea canadensis). Deep water plants such as water lilies (Nymphaea), have leaves on the surface which help to shade the water from sunlight, which can cause algae to grow. Water lilies like still water; ideally about half the surface of the pond should be covered with these. Marginal or emergent plants which grow in the shallows, offer shade and cover for animals. Dragonflies and nymphs use them to crawl out of the water and pupate. If you want bulrushes, I would avoid Typha latifolia and Phragmites communis which can be invasive, and use Typha angustifolia instead. Other marginal plants you could use include Iris pseudoacorus, the native yellow flag iris, Butomus umbellatus the flowering rush Caltha palustris, marsh marigold and Myosotis scorpioides, water forget-me-not. The best time to plant these is April to early May.
If you have room for a bog garden alongside the pond, this will extend the range of interesting plants you can grow and the type of habitat available to wildlife. Line your bog garden with a heavy duty butyl liner sandwiched between geotextile layers, perforate it to allow for some drainage and prevent stagnation, and fill with low nutrient clay. There are a great many plants to choose from including Irises, Filipendula, Ligularia, Rodgersia, Gunnera, Eupatorium, to name a few. Again, if you want a good job, I would suggest having it professionally designed and built.