Diarmuid Gavin: Plant up your pond
My pick of the aquatic plants you'll need to create a healthy, happy ecosystem
Last week we took a look at how to create water features for your outdoor spaces. This week is all about planting up a pond. The water is warm and aquatic plants are growing vigorously... so where do we start?
After sound construction, a good combination of planting is key for a healthy pond. Oxygenators are necessary to keep the water clean, as they suck the nutrients from the water which otherwise encourage a blanket of green algae. Hornwort and the water buttercup are a good choice here but avoid Elodea, Canadian pondweed, as this is extremely invasive.
Floaters are just placed on the surface of the water and provide some additional surface cover and food for fish. Duckweed (Lemna) and fairy moss (Azolla) tend to take over very quickly and carpet the pool. Choose instead native plants such as frogbit (Hydrocharis), which has pretty white flowers in summer, and water soldiers (Stratiotes) with spiky foliage. Don't worry that these plants disappear in winter - they sink to the bottom of the pond to overwinter and will re-emerge!
Buy the appropriate-sized basket (pot) and soil-based compost as recommended by the garden centre. If you have to repot your chosen specimens before setting in the pond, water well before placing. When you do place in the pond or container, make sure the plant is about 10in below the surface of the water. You may have to prop the pot up on some carefully placed bricks to reach this height. As your plants grow, lower the levels of brick until eventually your pots/baskets sit on the bottom.
Remove any decaying vegetation such as dying flowers or damaged foliage. Try to ensure that roughly 60pc of the surface of the water is covered by foliage and add some oxygenating plants to complement the aquatic ecosystem. Introduce some fish, but not too many, and don't add additional feed to your plants, as that can encourage algae. Ask your local stockists for recommendations of species.
Waterlilies (Nymphaeaceae, pictured) are the pre-eminent garden pond plant. They prefer non-moving water and a temperature that is fairly constant. Pick the sunniest part of your pond, as they love light and warm conditions and won't flower well in shade.
Buy them in a garden centre that specialises in aquatic plants, to get the best guidance. Check that the stock beds haven't been infested with aquatic weeds... you only want to buy the lilies, not a piggyback species that may become invasive overnight.
Ensure you choose plants that are just right for the size of pond or container you have. Varieties vary from dwarf to ones which are greedy for space. And make sure that the plants look healthy.
Waterlilies have achieved merit status with the Royal Horticultural Society. For small ponds or containers, try Nymphaea 'Pygmaea Helvola'. They have sweet-looking green leaves with some purple markings and spread 1ft-18in. They produce canary- yellow blooms through the summer.
Nymphaea 'Paul Hariot' will thrive in medium-sized ponds. It has purple leaves and one plant will reach a spread of around 4ft. The beautiful, dramatic flowers change from apricot to pinkish-orange as they mature. Nymphaea 'Escarboucle' produces red flowers and has a spread of up to 8ft. The blossoms can reach a width of 1ft through summer but you will require a pond with a depth of 3-4ft to sustain growth and spread.
If floating lily flowers are the stars of water flora, there's another category which shouldn't be overlooked. Marginals naturally grow in the shallow edges of ponds so these are appropriate if you have a pond which slopes gradually, or the pond has a shelf at the side around 6in depth.
While they aren't necessary for healthy pond life, they play a role in softening the edges of a pond, creating a naturalistic effect.
There are plenty of suitable plants, such as yellow iris (Iris pseudacorus), the flowering rush (Butomus umbellatus) and the pickerelweed (Pontederia cordata), which has cylindicral spikes of blue flowers. For drama, you can't beat the white arum lily (Zantedeschia).