In praise of pretty perennial nasturtiums
Enjoy their flowers from now until late summer
What’s not to like about nasturtiums? For many of us they were the first plants we grew as the seeds of annual types are large enough for children to handle and sow easily. The popular annual,
Tropaeolum majus, is edible and used as a companion plant (it lures aphids away from beans). It’s for all these reasons that I’m thrilled 2019 is Year of the Nasturtium.
Not all nasturtiums are annuals, however. I grow perennial types that aren’t as easy as annuals but are worth the extra effort. My favourite of the perennial climbers is Tropaeolum tricolor. Although the much-loved annuals are summer-flowering this climber is an early starter and I’m expecting flowers in the next few weeks.
It’s kept in the frost-free greenhouse until the frosts pass us by, but if you grow one undercover, you’ll be ushering all your guests into the greenhouse to look. The RHS give this plant a hardiness rating of H2 – tolerant of low temperatures but not surviving being frozen. For those without a greenhouse you’ll be pleased to hear I’ve known it to grow at a pace in a north-facing, glass porch. I would keep it out of direct sunlight in a south-facing position as this will cause the foliage to scorch. How to grow Visitors to the garden are always intrigued by this tropical-looking plant, that has tubular flowers of orange, yellow, red and purple. Each flower is about 2.5cm (1in) in length. For success grow the tubers in a pot of loambased compost and push some hazel twigs into the compost so it can scramble up to its 1m (3¼ft) height on its own. You’ll read that the very thin stems can grow to over 2m (6½ft) but they’re so fine they tend to flop and make an attractive mound over the twig supports, so 1m (3¼ft) is tall enough. In late November new foliage arrives which is delicate, and leaves look like a five or six-leaved clover. Shortly afterwards the flowers appear in late February or March. In May I move this plant outside and place it in a sheltered spot and once the flowers have faded at the end of May it’s placed back under cover to rest. The plant is summer dormant, so when most other nasturtiums are in full growth this stunner enjoys a well-deserved beauty sleep and the foliage quickly fades away. My potted specimens are rarely watered over the summer. Plant the tubers whenever you like but keep them dry until September. Tubers aren’t easy to come by, but you can often find them at specialist plant fairs.
Another climber that’s trouble free and sparkles when grown through a yew hedge is T. speciosum (flame creeper). It enjoys having its roots in the shade and will romp up the hedge to about 2m (6½ft) in summer providing you with bright red blooms. If climbers aren’t for you then perennial
T. polyphyllum is tempting. I grow this in a south-facing, well-drained raised bed that’s topped with gravel and fronted with a drystone wall. A rockery is perfect for this hardy, tuberous perennial that almost slithers across the ground like a snake. The silver foliage alone is worth having but add the tubular, yellow summer flowers and you have a winner. The bees will love it as much as you.