Diarmuid Gavin: Perfect plants for the garden pond

Ponds are an important part of sustaining wildlife, and this common native is a welcome starter course for pollinating insects. Its large round or kidney-shaped leaves also provide good cover for frogs early in the year.

This month, the water lilies have bloomed, their exquisite petals opening daily to salute the sun. As well as their serene beauty, the large lily pads provide cover for fish and frogs. When planting, don’t put them in too deep — the leaves should be able to float on the surface of the water. They prefer still water and dislike the turbulence of fountains and pumps.

If the leaves are starting to be crowded and bunching up out of the water, this means your lily has become congested and will need dividing — a job that can be done in spring or autumn.

They’re vigorous plants and will respond to an annual spring feed. You can get special aquatic, slow-release fertilisers which come in a tablet form that you insert into the compost. Position water lilies in full sunshine for best performance.

The water mint, Mentha aquatica, is marching across the pond, as if on an invisible layer of soil. It will flower next month with pretty pale lilac flowers. These will attract tortoiseshell, peacock and comma butterflies and the leaves provide cover for dragonflies to lay their eggs. Water mint can be used as a flavouring in the same way as the garden herb. Like its terrestrial cousin, it’s pretty vigorous, so remove some of it if it is getting out of hand.

River horsetail, Equisetum fluviatile, has a prehistoric appearance, and fossil records indicate its presence 150 million years ago. Its strange stems poke out of the water, looking a bit like bamboos with dark nodes or joints. It’s an interesting addition to a pond and I also love the exotic appearance of Cyperus paperus, Egyptian paper rush. Unlike horsetail, this is tender so will need over winter care. However, in summer, it will be the focal point of your pond, its tall stems topped with feather-duster-like tufts with small flowers at the end of each.

Every pond needs its oxygenating plants, those that absorb carbon dioxide and breathe back oxygen into the water. Often they don’t look like much, for example the long green strands of hair that make up Hornwort (Ceratophyllum), but their work is vital for a healthy pond, competing with algae and absorbing nutrients. Buy them in bunches and drop them in the pond and let them go to work. You need around one bunch of these per square foot of water.

If you want something a bit more decorative, I’d recommend Water Violet (Hottonia palustris), which produces pretty lilac flowers above the water.

I wage a continual battle with duckweed, which loves my pond. Get yourself a net and fish out as much as possible. This is something you need to do regularly, however. It’s far less of a problem in the pond where I have water lilies — their wide leaves provide shade, which duckweed doesn’t like.

Plant of the week

Baptisia australis

Baptisia is sometimes known as False indigo because it was used as a dye but considered inferior to Indigofera, the original source of indigo. However, there’s nothing inferior about its violet blue, pea-like flowers, making this a very popular border plant. It has a deep tap root that will seek out water, making it quite drought tolerant but also, like other plants with tap roots, not great to move once planted or to lift and divide. Plant in full sunshine in well-drained or stony soil.

Reader Q&A

I’m potting a Bloodgood Acer in a 120-litre pot. Is this too big to keep it under eight feet? It’s currently five feet. Any advice for the best layers to put in the pot? Ken

The size of pot is perfect and will restrict the acer from getting too big while allowing its roots to establish nicely in your growing medium. Rather than worrying about the size of the pot, give some consideration to the planting medium. A maple such as this is going to love a good rich humus material but it is also important to have really good drainage, such as old terracotta crocks or a layer of pebble. How you look after the plant once its potted will be the secret — regular watering at this time of the year and supplementary feeding during its growing period will result in a healthy plant and a beautiful composition of pot and plant.

Submit your gardening questions to Diarmuid via his Instagram @diarmuidgavin using the hashtag #weekendgarden