Plants are an essential element in any water garden; not only do they supply a link to the rest of the garden planting scheme, but they also help to keep the water clear and supply oxygen for fish. They range from those species that require only their root tips to be moist to those that thrive in deep water.

The six classes of water plants are as follows:

1. Oxygenators

Oxygenators help to keep the water clean and clear by absorbing the dissolved mineral salts that might otherwise encourage algae growth. Without them, the surface of a pond could turn into a solid mass of green in just a couple of weeks. Their presence is therefore very important in any pool - but absolutely vital if you plan to keep fish.

Examples include curly water thyme (Lagarosiphon major), which has the added benefit of stems that are capable of hiding baby fish from predators. There are a number of oxygenators to avoid however, as they tend to become very invasive; these include broad-leaved pondweed (Potamageton natans) and Parrot's-feather (Myriophyllum aquaticum). Most oxygenators are best grown in containers to limit their spread.

2. Deep Water Plants

These plants thrive in water 30-90 cm (12-36 in) deep, and include species such as the water lily (Nymphaea), cape pondweed (Aponogeton) and water poppy (Hydrocleys). They tend to produce broad leaves that float on the surface along with attractive blooms in season. Not only are they eye-catching, but their large leaves cut down the amount of light that reaches the pond, reducing the production of algae.

3. Surface Floaters

Floating water garden plants have hair-like roots that project into the pond and so obtain all their nutrients directly from the water; they do not need to be planted in soil. As they absorb minerals from the water, they assist in keeping the pond water clear which can be very useful when establishing a new pond. However, as the pond matures, you may want to remove some of the floaters in favour of more ornamental deep water plants.

Examples include water chestnut (Trapa natans), water hyacinth (Eichhornia crassipes) and water soldier (Stratoites aloides).

4. Maginals

Marginal plants grow naturally in mud at the edges of pools or in shallow water about 7-15 cm (3-6 in) deep. Consequently, the majority of ponds are equipped with a planting shelf just below the water line to accommodate these plants.

Marginals often have decorative flowers or foliage, and can also provide cover for wildfowl and other small creatures. Although they can help to shade the water, their prime function is ornamental; without them, the pond might look stark, dull and too horizontal.

Examples include water plantain (Alisma plantago), blue water iris (Iris laevigata), bulrush (Scirpus zebrinus) and arrowhead (Saggitaria japonica plena). Some species such as water mint (Mentha aquatica) and brooklime (Veronica beccabunga) also help to oxygenate the water.

5. Bog Plants

Bog-loving plants thrive in the moist, shallow areas that border the pond. However, care must be taken when planting them next to a pond as their roots may penetrate the liner and cause the pond to leak. Some example include: false goat's beard (Astilbe × arendsii), bleeding heart (Dicentra spectabilis), giant rhubarb (Gunnera manicata) and varieties of Hosta and Iris.

6. Moisture Loving Plants

These plants prefer a soil that is moist, but not waterlogged and look effective when planted around natural, informal pools. Examples include groundsel (Ligularia) and Himalayan cowslip (Primula florindae).