Like Brits heading for the Costas, zinnias are happiest when basking in the sun

A new week, a new month, but the same series. But were have made it to Z, and this is the end.

When I started gardening it was drilled into me that zinnias were not worth growing: they needed too much heat, hated rain and being transplanted and they were useless in our climate. But I saw them growing and blooming and there was so much to like about their rather prim and starchy flowers that I tried them, and discovered that they would grow in climates cooler than their natural homes in SW USA and Mexico.

Zinnias (named after Johann Gottfried Zinn) are not all annuals, some are shrubs, but we are only concerned with the annual ones here. The big-flowered, tall zinnias are derived from Z. elegans and may now be called Z. x hybrida. They come in a wide range of colours and flower shapes, including the currently popular scabious-shaped (above) and loosely formed but spectacular cactus-flowered and in the brightest of reds and well as amazing greens. These are all rather sparsely-branched, upright plants, ideal for cutting – and few flowers last better in water than zinnias. From a garden display perspective, other species and their descendants, with basal branching, smaller flowers and a more spreading habit are better. But it must be said that plant breeders have done sterling work when it comes to zinnias and there are some wonderful new varieties.

Zinnia angustifolia has a compact habit and narrow leaves, in pairs as with all the genus, and rather delicate, narrow-‘petalled’ flowers. It was used as the basis for the hybrid Z. x marylandica, created at the University of Maryland in the 1980s which is most often seen as the brilliant ‘Zahara’ series – compact and colourful and the best of all zinnia worlds. Zinnia haageana has blooms with zones of colour and a mass creates a tapestry effect – well worth trying. And then there is Z. tenuifolia, a straggly plant with small, bright red flowers with thin, sparse petals. Often sold as ‘Red Spider’, though I am pretty sure it is the straight species, it is pretty in a strange and subtle sort of way and if you like your zinnias big and bold you will be bitterly disapppointed.

Butterflies will not be disppointed though, whatever kind you grow. This has been a case of littering the words petal and flower with apostrophes so I do not offend the pedants. These are Asteraceae after all and each ‘flower’ (there I go again) is truly a head of lots of flowers, the outer florets being flat and petal-like and the central, disc florets being relatively inconspicuous. But, in zinnias, those disc florets are pretty showy in their own right. As they open, they form a ring of spidery golden flowers and these are heaven for butterflies, as well as bees.

So, choose your seeds carefully, making sure that you have tall ones with the big flowers if you want them for cutting. I have to admit that I am always scared to cut the first flowers because, if I need anything longer than a 15cm stem, with more than one or two nodes (and pairs of leaves) I find I am cutting off a lot of unopened buds. Fortunately, all things being well, zinnias grow very quickly. So, having dealt with their merits, how do we grow them?

Robinson wrote ‘ They are among the most effective of summer-blooming plants and they flower well until autumn. Their blooms are not easily injured by inclement weather, but retain freshness and gay colour when many flowers present a sorry appearance.’

He was clearly a fan. But her warned ‘Zinnias are always attractive but require a deep loamy soil and a warm open situation… Nothing is gained by sowing before the middle or end of March, as if the young plants have to stand before being planted they become root-bound and seldom fully recover.’

Zinnias also hate to be transplanted so, although these are half-hardy annuals we can’t treat them casually as we would marigolds. Young zinnias also hate cold, wet compost.

So we know that they dislike root disturbance, hate the cold and wet, dislike being stunted in pots and need warmth and sun.

That leaves us a few options.

We can sow, direct, where they are to bloom, in a sunny spot in late April. The trouble with this is that zinnias seeds are often expensive and casting them into the garden to the mercies of the weather with herds of snails and slugs passing by every night is nerve-wracking.

So I prefer to sow in cell trays. They are the last seeds I sow in spring, in April under glass. It is actually useful because a lot of the earlier annuals are now out of the propagator and I only have beans, courgettes and other squash in there. I fill the cell trays, water to firm the compost and put two seeds per cell and cover with compost. They germinate quickly and seedlings are usually showing within a week at 20c. They are hardened off and one of the seedlings pinched off if both grow. DO NOT remove all the smallest seedlings, if both grow, if you have sown a mixture – often the smallest seedlings grow into the best colours!  Then plant them out as soon as they have a couple of pairs of true leaves. And protect from molluscs.

You then just have to hope for a good summer. If, like me, you live where summers can be unpredictable – which basically means just the opposite – predictably wet – you need to find a sheltered, warm spot in full sun. They do well in patio pots in nice, comfy multipurpose compost, as long as they are well fed and watered – and I would use the shorter kinds for this. I planted a few in the polytunnel last year and they did fine, but then so did those outside, to be honest.

Cold, wet weather results in botrytis and mould – you just can’t avoid this. But when they are shining in the sun with their prim, almost artificial flowers, they are worth all the worry.

Would I grow them every year? Well yes, I would, and I do. After all, the one week I don’t by a lottery ticket could be the week I win, and the year I don’t grow zinnias will probably be the warm, sunny year when they would have done really well! I can’t risk that!

how to grow zinnias