February 2018 - Dahlias

Crocus Caretip

It may not be wonderful gardening weather this month, but the days are appreciably longer and the strength of the sun is improving day by day, hinting at the promise of the year to come. The ground is already warming up and it’s time to start thinking ahead and that’s one of the advantages of being a gardener. You’re always thinking six months in advance so summer’s in your mind long before it arrives, even on the dullest of winter days.

There’s one colour-packed plant with enough flower power to straddle summer and autumn and it’s the dahlia. The taller ones are superb in the garden and there are diminutive beauties for patio pots. They cut well and they come in every shade, including those elusive sultry reds that add so much opulence to autumnal golds and mauves. They vary in form, from round pom-pom to bee-friendly single. There are also gentle waterlilies and cactus dahlias that explode like fireworks in the border. Or you could go for giant, attention-seeking decoratives because they’ve never been more popular.

If you’re a cut flower lady, or gentleman, dahlias should be on the top of your list because they’re ‘cut and come again flowers’ that persist for weeks on end. Pick them twice a week and they’ll go into November - if the frost allows. Although they’re not great at struggling up through other plants, you can add them to the garden in two ways. They’re perfect for cutting gardens, bedded out in straight lines. Or you can create gaps for them in the borders, by giving them a dedicated space. Fill the gap with spring bedding, such as tulips, wallflowers, pansies, polyanthus and forget-me-nots for instance, and then remove the plants at the end of May. Place your dahlias in the gap in early June. Dahlias shouldn’t go out before early June, because they’re not only susceptible to frost damage, but cold weather retards them.

The best way to grow from the garden is order tubers now whilst there’s a good choice. Keep the tubers in a cool frost-free place until March and then plant them in a good compost in large pots. Keep your potfuls in a frost-free greenhouse if possible. Dahlias respond to warmth and they will shoot as the temperatures rise. Once the shoots get to four inches or so in height pinch out the tops to make your plants bush out and then plant them outside in June. You can also take cuttings from the pinched out tops.

Dusky dahlias in shades of red look so good with warm orange, purple and lime-green, whether in the garden or in a vase. The average dahlia lasts for four to five days in water, but the Dutch-bred Karma range has been bred for cut flower use so Karma varieties last a couple of days longer than the others. The dark stems are almost rubbery to the touch and the flowers are held well above the foliage. ‘Karma Choc’, a deep red with dark foliage, is in the top rank. Other good sultry forms include the spiky Nuit d’ete, the similar ‘Rip City’ and the strong growing ‘Chat Noir’. These rise up to three feet, but ‘Arabian Night’ is a taller more upright dahlia that produces lots of flower in the brighter shade of dark red. There are also two collections, 'Opulent' and 'Dark-Flowered' containing some of these sultry dahlias.

Some dahlia varieties seem to go on forever and the 1920s’ peony-red semi-double ‘Bishop of Llandaff’ is admired as much for its dark ferny foliage as its bee-friendly flowers. It’s ability to perform in cool and hot summers alike sets it apart and it’s spawned many single-flowered children all christened Bishops. None are quite as good as the original ‘Bishop of Llandaff’. However one seedling is a close rival and that is the soft orange ‘David Howard’, a fully double decorative with khaki foliage. It’s been around for sixty years and is still first-rate. ‘Thomas A. Edison’ (1929), a strong purple decorative, is another great survivor and of equal merit, standing out among others because it rises to four feet in height. When plants are popular for years it says a lot about their constitution and their charm. ‘Purple Haze’ is another reliable purple that pushes out lots of flower.

There are lots of warm oranges on offer and these glow in the garden or vase, adding a golden touch that matches the mood of autumn. Many of these warmly tinted dahlias have sultry foliage too, so they add a lot to a border. ‘Jescott Julie’, known as a double orchid because the two-tone pale orange and apricot-orange petals are long, is another excellent dahlia for the front of a border. These are warm, soft oranges, but there are day-glo orange-pink dahlias that hover between pink and orange like shot silk. They include ‘Karma Fuchsiana’, a very popular cutting dahlia. There’s also a Burnt Orange Dahlia Collection that contains warm oranges and yellows.

Paler warm-tinted dahlias are highly popular because they come in unique colours. ‘Gallery Leonardo’ a soft, salmon-pink, is one of the best of the Gallery Series. These are shorter dahlias designed to be grown in containers. And then there is the coffee and cream coloured ‘Cafe au Lait’, a florist’s variety which has large flowers. These dahlias look terrific in a vase alongside stronger reds, but they do need careful placing nearer brighter ones in the garden setting.

There are also soft whites and pale yellows and these mingle well in vases of deep reds, strong purples and pink-purples. ‘Eveline’ is a top quality dahlia in vase or border, and the purple tinting on white petals adds vibrance and warmth. ‘Lake Carey’, ‘Diana’s Memory’ and ‘Lady Kate’ all come in white shaded in mauve and purple. Soft yellows are also popular and ‘Glory van Heemstede’ is the colour of lemon syllabub. It would be a perfect contrast planted close to blues and mauves and there’s a 'Blues and royals' collection containing ‘Blue Boy’, ‘Blue Wish’ and ‘Purple Haze’. Add a stronger vibe with 'Irresistible pink' dahlias, which blends rich pink varieties.

Pom-pom and ball dahlias are petal-packed flower sculptures and they offer a contrast to open-faced decoratives and spiky cactus dahlias, as well as lasting well in the vase. Pick one, just one, and place it in a posy vase to create plant perfection in seconds. The reddish-purple ‘Downham Royal’ has been popular since 1972, when it was launched, and deservedly so. The butterscotch-orange ‘Sylvia’ has exactly the same soft ball shape. ‘Wizard of Oz’ is a soft pink with green undertones. ‘Rocco’ is a deep purple and ‘Red Fox’, is a rich red. Or you could go for the 'Ruby and amethyst' collection, all ball dahlias in jewel-box colours.

Single and open-centred dahlias are also highly popular because they produce lots of simple flowers that happily mix with asters and other daisies, whilst attracting bees and butterflies. Many have dark foliage and these include the white semi-double ‘Classic Swanlake’ and the single ‘Twynings After Eight’. The latter is a substantial dahlia with mauve tinting on the white flowers. Anything with the Bishop in its name is also a bee-friendly single. Dahlia Star Wars is perfect for a patio pot and the apricot single flowers stand out well against dark foliage. You can find dahlias like these in our collection of 'Blockbuster dahlias for bees, butterflies and pots'. Slugs can be a problem, so avoid pots with a rounded lip at the top, because slugs can hide between meals. There’s also more deadheading because the flowers go over far quicker than doubles.

The star-shaped dahlias, such as ‘Honka’, make quite an impact in the border because they produce lots of minimalist flowers. In autumn light, they look like giant spiders and the yellow ‘Honka’ was used to great effect in the double borders of RHS Wisley.

At the other end end of the spectrum are the sock-it-to-you dahlias with very solid middles and they include the blood-orange fuzzy ‘Mel’s Orange Marmalade’ and the blue-purple ‘Bayou’. If bigger is definitely better, go for ‘Vancouver’ a massive rather shaggy purple dinner plate.

Do I Lift Them?

This depends on where you live. If you’re in a milder position of the UK in most years it will be fine. However there’s always a risk you’ll lose them. There are two problems to consider too, if leaving them in. Dahlias shoot very late from the ground, sometimes as late as May, so they create a gap in the border that can be a waste of space in smaller gardens. The other problem is that dahlias develop large tuberous roots, when left in the ground for a few years, and this limits flowering, so you have to lift and divide every third year or so even if you opt to leave them in.

How to Lift and Store

After the frost has cut down the dahlia, cut the stems back to three to five inches and lift the tuber, gently shaking off the soil. Make sure there’s a label. Store the tubers in a frost-free place in dry compost. Under the greenhouse bench is fine as long as there is a frost-breaking heater. Deep plastic crates with holes in the side are ideal. Fleece them in severe winters.

Cut Back Summer-flowering Clematis
Cut back summer-flowering, small-flowered clematis to the lowest buds. These flower in July, August and into September and this includes the viticella types.
Finish Pruning Roses
This should be done as soon as possible. Aim to create an airy shape on your roses and remove the 3 Ds, any dead wood, any dying wood or anything that looks diseased. Hybrid teas can be cut back to between 10 -15cm. Floribundas should not go lower than 45cm. Shrub roses and English Roses should be cut back by a third.
Order Seeds
These will be going quickly so order all your seeds as soon as possible. Write labels so you’re ready to go.
Sow Annual Umbellifers
If you didn’t sow your umbellifers in autumn, sow as soon as possible to get larger plants of Orlaya grandiflora and Ammi. These both have tap roots, so prick out the seedlings as soon as possible into individual 9cm pots. Add perlite to the compost to help germination.
Prepare for Sowing and Planting Outside
Get the ground ready. Rake through plots already dug over and turn and weed any that are still not done.