Aquatic Gardening

There are several points you need to consider before building your pond or water feature. Should it be formal or informal, natural or modern? Do you want to keep fish, grow plants or attract wildlife? Are there children to keep safe?

Once you have answered these questions you need to decide where you want to site the pond or water feature. A pond should be kept away from big trees and shrubs so ensure their roots don't puncture the lining. If you want to keep fish you need to have a pretty deep pond to stop it freezing over the winter. The smallest you should build a pond is 60cm (2ft) deep and 1 x 1.5m (3 x 5ft) across. However, the bigger the better.

If children's safety is an issue or you prefer not to have to maintain a pond then a water feature is an excellent compromise. You could build a wall fountain or a pebble pool which can be sited in sun or shade near to a power supply. If you do not have external power then a wide plant container or half a barrel, without drainage holes, is ideal. You can still grow small aquatic plants or use floating oxygenators such as water hyacinth. You will need to protect them during winter or empty the container and start again in the spring.

Ponds

Formal ponds tend to be circular or rectangular with straight, steep sides. They are mainly used to grow water lilies or to keep fish. Informal ponds can be any shape you wish and usually attract wildlife. As fish tend to eat eggs, larvae etc. you are best not keeping fish if you want a true wildlife pond. You will need to build in a few planting shelves around the edges and at least one sloping side to allow creatures to climb out. All sorts of plants can be grown in an informal pond from marginal plants, bog plants or deep-water plants. Which ever plants you choose you must include oxygenators to ensure a good healthy environment for wildlife and plants.

Looking after your Pond
Spring: most ponds will turn green in spring but it will clear itself in a few weeks. However, new ponds could remain green for up to twelve months. Pull out blanketweed and leave on the side for a day or so to allow creatures to escape back into the pond. Remove duckweed with a small fishing net.
Summer: Feed fish between May and September. Pull out oxygenators if they threaten to take over the entire pond.
Autumn: Remove excess silt from the bottom of the pond leaving about 1 inch to allow plants to root. Remove floating plants once the die, cut down marginals and pull out dead lily leaves. Keep autumn leaves out of the pond by covering with a net.
Winter: If you keep fish place a plastic ball on the surface to avoid the pond freezing over totally. If you don't keep fish there is no winter maintenance required.

Building a Pond
The easiest way to build a pond is to use a butyl rubber or plastic sheet. To work out how much to buy, dig your pond to the size and shape required then measure the length, width and the deepest point. Multiply the depth by two and add to the length then again to the width. Add 50cm (20in) for overlap on both the length and the width. This is the size of sheet you need.
When digging the pond ensure that the bottom is firm and flat and free from stones. At least part of it needs to be 60cm (2ft) deep for fish and deep-water plants the rest can be 45cm (18ins) deep.
Build in some shelves around the sides 15cm (6ins) wide and 20cm (8ins) below the surface. Slope one side to allow wildlife to escape. Ensure that all pond sides are level by using a spirit level, don't use your eye.
Spread 2.cm (1in) of soft sand over the base, shelves and slopes then cover with pond underlay followed by the liner.
Start filling the pond. Once full, trim the liner to 30cm (1ft) overlap. Cover the overlap with paving stones or turf. Make sure no liner is exposed to the sun as it will rot.
Lower the plants into place. Wait six weeks before introducing fish.

Water Features

You can buy basic bubble pool kits at most garden centres and they can be adapted to any type of water feature. The kit consists of a reservoir with lid, a pump and water outlet spout. The reservoir is sunk into the ground and filled with water. Place the pump at the bottom of the reservoir on a couple of bricks to keep out silt. Place the lid on top and feed the water spout through the hole onto the pump. Once it is in place add a decorative finish such as pebbles, slate, gravel, millstone, etc. When it is turned on the water will spurt through the spout and fall back into the reservoir and recycled. You may need to top up the reservoir during very hot weather.

Water Plants

There are four types of water plants: deep-water aquatics, marginals, submerged oxygenators and free-floaters. For your pond to remain healthy you will need a few plants from each type except free-floaters.

Water plants tend to be grown in plastic baskets which stand on the planting shelves or floor of the pond. When you buy a new plant it will tell you the depth it likes. Note that it is the depth of water over the top of the roots not the depth of water it stands in.

Plants should be divided only when they stop flowering which could be as long as seven years. Lift the basket out of the pond and remove the plant. You may need to cut the basket away if the roots have grown through the sides. Split the clump as you would a border perennial. Choose a strong piece with healthy young shoots and replant into a basket of aquatic compost. Don't use normal potting compost and be careful not to use pesticides or weedkillers anywhere near the pond. Top off with gravel to hold the compost in place. When repotting waterlilies ensure the rhizomes are sitting on the surface of the compost. Sink the basket back into the pond.

Marginals
These plants grow in shallow water round the edge of the pond. They not only look good their roots use up lots of minerals which would otherwise feed algae. Examples of marginal plants include Japanese water iris (iris laevigata), the cardinal flower (lobelia cardinalis) and flowering rush (butomus umbellatus).

Deep-water
These plants grow in much deeper water and should be placed at the bottom of the pond. Waterlilies are a deep-water aquatic but they like still water, don't plant near a fountain or waterfall. Examples of deep-water aquatics include water hawthorn (aponogeton distachyos), arum lily (zantedeschia aethiopica) and waterlilies (nymphaea)

Oxygenators
These plants live under the water and the provide oxygen used by fish and other pond-life. Be careful which oxygenators you choose as many are invasive. A good one is Lagarosiphon major which is evergreen and can just be dropped into the pond to root at the bottom. It will need to be weeded out every so often. Another good example is the water crowfoot (ranunculus aquatilis).

Floating Plants
Free-floating plants provide shade to a pond. Some are not hardy and will die in winter, some duck down into the water for winter and reappear each spring. An example of a tender floating plant is water hyacinth (eichhornia crassipes) and frogbit (hydrocharis morsus-ranae) will come back in the spring.

Bog Gardens

If you have an area in your garden which never dries out, the easiest way to deal with it is to turn it into a bog garden. Bog gardens look particularly good next to a pond. This can be achieved by extending the pond liner into the required area and piercing it with a fork to allow some of the water to drain away. Add garden soil enriched with well-rotted garden compost or manure ensuring that the compost cannot fall into the pond.

You can plant any moisture-loving perennials or marginal plants that like very little water over them. Examples include hostas, primula and mimulus cardinalis.