Helen Yemm on how to grow spring flowers

This week Helen Yemm advises on making the most of delightful native fritillaries, taking care if you’re pruning a lively pieris, and how to avoid accidentally injuring yourself in the garden...

A reader at an informal “Thorny Problems” session in Dorset recently asked for more advice on growing Smyrnium perfoliatum, a late-spring, glowing lime-green biennial umbel (often mistaken for some kind of euphorbia). She’d had little success in the past – is there a knack?

Not exactly, is the answer, but it is important to understand a thing or two about the way the seeds and seedlings behave in order to establish the permanent ebb-and-flow colony sought by an increasing number of “Smyrnophiles”, it would seem.

First, as is the case with many members of this “cow parsley” plant family, you have to mimic nature and sow seeds promptly, when fresh. Allot them a specific site, rather than just cast them around, so you can monitor their presence. Second, on germination, the double or triple seed leaves bear no relation to the rather coarser adult leaves of the plant and appear to die off completely during their first summer.

This is the point at which you may lose heart and even plant something else in their stead. However, if undisturbed, the tiny dormant plants will put in an appearance the following spring, producing bold, shiny leaves not unlike celery, growing extremely rapidly to around 16in (40cm) and flowering in May/June before setting masses of black seed.

So where do you start? Single, eye-catching plants are often sold at fairs and gardener gatherings in late spring. Pounce on one or two, enjoy the flowers and let them go to seed (to start the process described above). Or carry an old envelope in your glove compartment and beg some seed from a successful Smyrnophile (who’s bound to have plenty to spare), head home and sow straight away.

Snake’s head fritillaries

These little native fritillaries, with their delicately patterned nodding flowers, grow from bulbs that are most often planted in September, along with other spring stars, such as alliums and daffodils, and they flower the following year in early to mid-April. They tolerate some shade, and thrive and multiply most rapidly by self-seeding in soil that is heavy and damp.

Although they make pretty front-of-border plants, they look best growing en masse in grass that doesn’t have to be cut in early spring and can be left un-mowed until at least late July or August. Recognisable seedlings produce two leaves in their first year, and may flower in their second or third.

If you are impatient and/or gardening on a small scale (and little self-seeding patches do look quite enchanting if you can spare a lawn-corner somewhere), you could buy a few pots of flowering bulbs around now, plant them in short turf that does not dry out too drastically in the summer and allow them to just set seed and get on with it, adding more bulbs in September.

Pruning overgrown pieris

You certainly can prune your pieris. Like other spring-flowering woodland evergreens such as camellias and rhododendrons, pieris can be cut back immediately after flowering. Your shrubs will then, in theory, flower on the new growth they make subsequently, but very possibly (depending on the variety and on how radical you were with your pruning saw) not for a couple of years.

You don’t say quite enough about these shrubs. Are they forms of P. formosa (the largest) or the slightly smaller P. japonica? Did you cram them into too small a space when you acquired them (in which case they are probably quite young, and could be moved rather than pruned) or are they ancient whoppers on which the whole garden depends for structure? Or have you one of each?

Either way, I advise you to be cautious: both species are quite slow-growing, and depending on their age and situation, may not recover quickly – and pruning these woodlanders hard is not something you want to be doing very often or they will rarely flower well. But if prune them you must, perhaps cut one back quite hard this year and see how it responds before handing out any stern treatment to the other.