Ponds and Trees

There are few things which look quite so magical as the reflection of trees in water – their sweeping foliage bowing down to touch the water. While the image might be an appealing one and although trees and ponds can co-exist, their relationship does need a little bit of careful policing at times, if it is not to all end in tears.

Trees certainly have their benefits – and high on the list is the shade they offer. A pond – especially a small and relatively shallow one – exposed to full sun throughout the day will heat up alarmingly, which is no good for anything living in it, be it fish, frog or plant-life. In addition, the abundant light may also help promote the growth of algae, bringing the twin scourges of blanket weed and green water. With the shelter of a tree, however, fish and wildlife can seek out the shade when the rest of the pond is getting too hot and there is not so much light available to drive algal blooms so readily.

Tree Problems

However, many pond-keepers are of the opinion that the good that trees can do is vastly out-weighed by the potential trouble they cause. Some trees are poisonous, for instance – laburnum being a well-known example – while bay, laurel, yew and lime may also cause problems, particularly for fish ponds. Others have particularly deep roots and can affect the structure of the soil by significantly lowering the water table – poplar, for instance, are particularly thirsty, while willows are far less greedy and some pond-keepers insist that you should never site a pond beside sycamore.

There are many anecdotal tales of tree roots damaging liners too, though perhaps the biggest problem with trees near ponds is their leaves. The annual leaf-fall in autumn can contribute vast amounts of organic material to the pond in a very shot space of time. Coupled with the gradual slowing down of biological activity as the water temperature falls, this can store up problems for the winter – and fuel major algae problems in the spring. Fitting the pond with a pond net is the only way to avoid routinely raking fallen leaves out of the water.

Suitable Trees

Fortunately a number of ornamental trees can be trusted to sit alongside a pond without causing trouble – and if the pond is large enough to carry it off – the visual effect can be well worth the effort required to manage the leaves in autumn. The trick is to find a balance between the impact of the foliage, fruit and flowers and the potential damage to the aquatic eco-system. For the newly-built garden pond, a tree which grows to maturity fairly quickly is usually called for, though one which ideally remains relatively small. The Mountain Ash and its relatives (Sorbus sp.) are hard to beat for an impressive and showy spectacle of berries and foliage – while remaining fairly compact, with a non-invasive root system. They are an ideal choice for the wildlife pond too, providing a great source of winter food for wild birds.

A variety of other small trees are worth considering, including the various forms of Willow (Salix sp,) Siver Birch (Betula sp.), Crab Apples (Malus sp.) and the May or Hawthorn (Crataegus aestivalis) – not forgetting its cultivated forms, which provide great autumn colour.

Trees and ponds can successfully sit alongside each other and for those of us planning a new pond – or selecting what to plant around it – avoiding the main pitfalls can be fairly straightforward. Inheriting a pre-existing pond amid trees can, however, inevitably pose a bit more of a challenge. Even so, with careful management and an understanding of the potential problems, trees and ponds can be complementary – rather than conflicting – elements of the garden.