A Drop of Exotica: Water Hyacinths
If you've got a taste for the tropical and your pond is nestled in among exotic Colocasia, canna lilies or bananas, this is the water plant for you.
Mind you, if you're growing it for its flowers it can be a bit of a lottery. It has its roots in hotter climates than ours, it doesn't always flower in the UK unless we have a good hot summer.
If that is the case, you'll be rewarded with that lovely flower stem with clusters of pale lavender flowers, stained darker blue on the top petals. Think of this as hitting the jackpot: most years you'll only get leaves, but what wonderful leaves they are.
Look closer and you'll see bulbous, air-filled spongy sacs at the base of each stem, allowing it to float freely on the surface of the water (no fiddling about with aquatic pots and compost required). The dense purple-black roots hang down into the water below, feeding from nutrients in the pond - and water hyacinths are greedy enough to give even the most rampant algae a run for their money. That means if you suffer from green water or blanketweed, water hyacinths can be a good way to keep the problem under control.
It can double its size in a matter of weeks: far quicker to cover a pond than a water lily, it's a great filler in a new pond where too much of the surface water is open to sunlight.
With that rate of growth, you might expect it to get troublesome, and indeed in its native waterways in warmer parts of the world, it's a real nightmare, highly invasive with a habit of blocking local waterways.
Luckily here a good frost will stop it in its tracks, so it's never had a chance to become a problem.
You can overwinter a water hyacinth: but you'll need a heated greenhouse, plus lots of light (not a feature of a British winter, on the whole).
We have no heat on the nursery, so we've never been able to keep it - and many people who have tried say they succeed until February or March but then fail. Most people just pull out their hyacinths at the end of the year and throw them on the compost heap. That might seem extravagant, but they're not that expensive and are available again from mid to late May onwards after the risk of frost has gone.