Pot luck: unusual patio plants that love water

Now’s the time when garden centre shelves are groaning with bedding plants destined to fill patio pots everywhere. With great reason – no other group of plants is as good at offering never-ending flowers throughout the summer.

However, there are downsides. The annual production of millions of bedding plants in heated conditions, only for them to be wiped out and rebought the next year, churns out a lot of carbon. Not to mention the expense of forking out for them every year. Most have lush growth, which means come mid-summer you’ll be out every day with the hose, especially for patio pots. They require slavish devotion and return a hefty water bill. An alternative that can add far more surprise and delight, for a lot less input, are aquatic marginals.

With massive architectural leaves and dazzling flowers, the large plants that grow on the banks of rivers or bogs can make excellent subjects for pots. Simply pick planters without holes to keep the moisture sealed in. Glazed ceramic filled with aquatic plant compost works a treat, as will many of the plastic, fibreglass or composite pots that are now sold with holes as “optional extras” to be punched though on their base. In my experience these require far less irrigation than porous terracotta or wooden planters filled with conventional bedding – more like once a week than once a day. For newbies, it’s also easier to get watering exactly right by simply keeping the level topped up to the rim of the pot, which takes all the guess work out of it.

Thalia dealbata.Photograph: Linjerry/Getty Images/iStockphoto

I love the elegant, boat-shaped leaves of the powdery alligator-flag, Thalia dealbata, that leap above the water’s surface on slender stems. Growing up to 150cm tall, its purple or white flowers that emerge on long antennae above the leaves perfectly complement its glaucous blue and silver foliage.

If you crave something graphic and minimal, the water horsetail – Equisetum hyemale – has it in spades. Looking like miniature culms of bamboo, just without the canopy of fluffy leaves at the top, it is central to modernist, Japanese-style gardening, yet is (perhaps surprisingly) a British native. Known for its extremely vigorous growth, it can be a real thug if left to roam in any water feature that isn’t lake-sized, so confining it to a patio pot is the only way to keep its megalomaniac tendencies in check.

If you are up for a little more work, in exchange for knock-out visual impact, you have to give the water canna (Canna glauca) a go. This has thinner leaves and much more delicate flowers than the big, blousy bedding types, and as the name suggests, requires boggy conditions to thrive. There’s also the wonderful imperial taro (Colocasia antiquorum “Illustris”) that kicks out enormous shield-shaped leaves in charcoal brown, with acid green veins. As with the water canna, it is not frost hardy so will need lifting in the autumn, overwintered as a house- plant, then planted out again next spring.

Email James at james.wong@observer.co.uk or follow him on Twitter @Botanygeek