Dahlias are demanding divas – but they’re worth it

Like so many gardeners of my acquaintance, I’m a dedicated dahlia-lover, a person easily capable of whiling away a winter’s evening or two by browsing the online catalogues of specialist suppliers in pursuit of the choicest varieties. The result is that the delivery of large packages of dahlia tubers is one of my guilty pleasures at this time of year. But it’s not just the thrill of virtual purchases made real that I relish. There’s also the tingle of excitement that comes with knowing that so much latent beauty is contained within those same fleshy root structures, magically hardwired into each dahlia plant’s genes as the result of centuries of promiscuous cross-pollination and careful breeding.

Bafflingly, the dahlia still has its critics. There are those, for example, who still see this genus of late summer/autumn flowering plants as brash and overstated, its showy blooms the floral equivalent of Coronation Street's Bet Lynch in a leopard-skin dress.Yet one of the things that distinguishes the genus is its huge variety of flower colours, shapes, heights and sizes. So if the flouncy, ruffled or quilled blooms of the big dinner-plate or cactus dahlia varieties just aren't your thing, then concentrate on the simpler, subtler, pollinator-friendly flowers of single flowering, collerette and star types as well as species dahlias. Examples include the Honka, Happy Single and Bishop series,  Twynings After Eight, Apple Blossom, Dahlia coccinea, D merckii and D spectabilis.

Vigilant protection

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Dahlias flowering in abundance in June Blake's garden in County Wicklow

The matter of their extravagant good looks aside, others argue that dahlias are demanding divas, requiring vigilant protection from slugs, snails and late spring frosts, as well as careful staking, regular deadheading and the very best of growing conditions – weed-free, moisture-retentive soil enriched with manure and seaweed powder, full sun, shelter and space – in order to flourish. All this is true. But just look at the rewards, which come in the shape of months of brilliant, bountiful floriferousness from late July until the first harsh frost.

Convinced? Then lose no more time in sourcing the tubers of individual varieties from specialist suppliers for potting on in February/ March. Recommended suppliers include all good Irish garden centres while for specialist online suppliers, see the stockists listed below (see this week's Dig In).

Tubers, as mentioned earlier, are the fleshy, overwintering root structures of these herbaceous plants, which are traditionally dug up each autumn and overwintered in a frost-proof garden shed. The best way to encourage them back into growth is to soak them in a bucket of lukewarm water for a couple of hours before potting them on into 2lt plastic pots, using a good quality, soil-based potting compost and making sure to plant to the correct depth so that the top of the tuber (the remains of last year’s flower-stalk) is just below the surface of the compost. If the tubers are large ones that you’ve dug up and overwintered yourself, then they may need to be divided before being potted up. Do this using a sharp knife, making sure that each division contains at least a couple of “eyes”, the growing points (much like potatoes) at the top of the tubers from where the new shoots will emerge. Water and label the pots carefully before placing them somewhere bright and frost-free but not too warm. A glasshouse or polytunnel is ideal, but a sunny porch or conservatory is fine while even a cold frame will do. Just make sure to give them plenty of frost protection on cold nights in the shape of layers of horticultural fleece.

You’ll also need to take very careful precautions against slugs and snails, which love to eat the emerging tender shoots. So sprinkle some organically-approved slug pellets on to each pot and make a habit of inspecting the emerging plants twice daily for any signs of damage (sharp scissors at the ready to slice any slugs in two).Water the pots regularly enough that the compost is damp but not sodden. Once emerging shoots have reached a height of 10cm, you could also take cuttings, an excellent and affordable way of increasing stock of favourite dahlia varieties. For a detailed guide to division and taking cuttings, see jrg-dahlias.co.uk.

Dahlias are also easily raised from seed sown under cover in February-March, a fast and affordable way of producing large numbers of plants. All you need is a basic electric propagator (the seed needs plenty of heat to germinate) and somewhere bright and frost-free to put the seedlings until they can be planted outdoors. Recommended seed suppliers include UK-based Chiltern Seeds (chilternseed.co.uk) and Avon Bulbs (avonbulbs.co.uk).

Whether raised from tubers or seed, your dahlia plants should only be planted outdoors (don’t forget to harden them off first) after all threat of frost has passed, typically mid- to late-May. Nip out the growing tips above the fifth or sixth  set of leaves to encourage bushiness, and continue to take precautions against slugs.

Kept staked and regularly dead-headed, these flowery divas will reward you with their sumptuous blooms for months on end.

THIS WEEK IN THE GARDEN…

While it’s still a little early to sow seed of most vegetables, others such as chilli peppers, peppers and aubergines all need a really early start in order to be properly productive. Bear in mind that their seed can be slow to germinate and need plenty of heat (25 degrees), so sow under cover, using an electric propagator if at all possible. Once seedlings have germinated, move them somewhere bright and slightly cooler (17-21 degrees) but away from direct sunlight and cold drafts. Pot on into individual small pots once the seedlings have developed their first set of true leaves.  Recommended seed suppliers include Cork-based brownenvelopeseeds.com and Dublin-based mrmiddleton.com

While onions are traditionally grown from sets (small baby onions), growing them from seed is a great way of avoiding the accidental introduction of soil-based diseases, allows you the choice of a far greater range of varieties and is considerably cheaper. Sow over the next few weeks, in gentle heat and under cover. Recommended stockists include Irish Seed Savers (rishseedsavers.ie) and Real Seeds in the UK (realseeds.co.uk)

Dates For Your Diary

Saturday 4th February (10am-1pm), Dalkey Garden School, Mornington, Saval Road, Dalkey, Co Dublin, Willow Weaving Workshop with Annmarie Bowring (€50 includes light refreshments), see dalkeygardenschool.com:

Wednesday 8th February (8pm), Kill O'The Grange Parish Centre, Kill Lane, Dublin 18, History of the Botanic Gardens, Plants and People, a talk by Paul Maher on behalf of South County Dublin Horticultural Society, (visitors €5);

Saturday, 11th February, Crown Plaza Dublin, Northwood Park, Santry, Dublin, the Garden and Landscape Designers Association (GLDA) celebrates its 21st seminar this year with guest speakers Sue and Bleddyn Wynn-Jones of the well-known Welsh nursery Crûg Farm Plants, Greek landscape architect Thomas Doxiadis, Dutch garden designer Noël Van Mierlo and British garden designer and landscape architect Emma Mazzullo, tickets €50 (students), €70 (GLDA member, pre-reg), €95 (non-members), price includes refreshments and lunch, to book, see glda.ie or telephone 01-2940092;

Weekends in February, Woodville Walled Garden, Kilchreest, Loughrea, Co Galway, Snowdrop Weekends every weekend throughout February (11am-5pm) with guided tours by head gardener Marie at 2pm and a special Snowdrop Day on Saturday, February 11th with guest speaker Assumpta Broomfield (from 2pm, admission €10), see woodvillewalledgarden.com