Dahlias have made more comebacks than the Rolling Stones. They are now fully liberated from allotments and competition growers, and grown in borders, containers and raised beds — anywhere they can be squeezed in. After centuries of breeding, dahlias are available in a kaleidoscope of colours, and when you combine this with the intricate range of flower forms the choice becomes huge. It’s a case of pick your favourites and off you go.
Dahlias have 14 classifications of flower forms, including single, cacti, pompon, ball and decorative. Some have dark bronze leaves, an ideal foil for the flowers, to increase the range further. They are surely one of the best-value plants too, producing masses of flowers from one tuber, and they make a fine, long-lasting cut flower to bring indoors.
How to grow and pot up your own tubers
If you are buying or have bought tubers or dug them up last year and stored them over winter, now’s the time to pot them up and grow them undercover. This gets them growing away nicely so that when the fear of the last frost has passed strong plants can be planted out and will flower earlier.
Half-fill a two or three-litre pot with some multipurpose compost. Place the tuber in the pot centrally with the stem facing upwards and backfill with more compost. It’s that simple. If you’re potting up your own tubers they will be larger (and may need a bigger pot), and the central stem will stick out the top — don’t bury it. Then label it, place somewhere light and frost-free (a greenhouse if you have one, or indoors where it’s light but away from central heating). Water thoroughly, then don’t water until you see shoots, then water regularly but only lightly.
Shoots will appear in two to three weeks. As these shoots grow, pinch out the tips of the main shoot down to the main leaves with your fingers, or use a sharp, clean knife. As it grows on further remove all but five stems (tough but worth it!), which will make it grow stronger. You can pot up the cuttings to make more plants.
Plant out in your garden — but wait until the last frosts
Dahlias are what we call “hungry plants”, requiring a rich, fertile soil that doesn’t dry out. They can cope with most average garden soils, but the more prep you do before planting the better the results will be. A sunny spot out of strong winds is best. Add plenty of organic matter or well-rotted farmyard manure, and a handful of bonemeal with each when planting. Plant potted dahlias to the depth they are grown in the pot. If you’re planting dahlias direct mid-May (which is possible, but they’ll flower later and less prolifically), plant the tubers horizontally about 12cm deep with their “eyes” (the nodules where the shoots come from, like a potato) facing upwards.
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Once in strong growth, feed twice a month with a liquid feed such as tomato feed, and do not let them dry out. Most will need staking, so ideally put your stakes in the ground early so as not to disturb the roots later.
When growing dahlias in pots and containers,choose shorter varieties that will look good in proportion to a pot. Use a peat-free multipurpose compost. Pots are particularly prone to drying out, so be vigilant with watering and feeding.
• The seven easiest dahlias for autumn
Deadhead throughout summer
To keep your plants flowering, deadhead when blooms have faded. What’s tricky is that once all the petals have fallen from a spent dahlia, the hard, green part at the base of the flower (the calyx) closes over, and what is left looks very similar to a bud. The difference is the buds are rounded and the dead heads are slightly cone-shaped.
Watch out for pests
Earwigs are the one pest to watch out for. They nibble soft young petals and leaves, stripping them or leaving large holes. The easiest way to catch them is to fill upturned pots with straw or shredded paper and place on canes next to plants. In the day time the earwigs will hide in the pots to avoid sunlight and you can then get rid of them.
My nine favourite dahlias
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Dahlia ‘Black Narcissus’
Stunning, dark, wine-red cactus form with medium flowers. Each long petal is slightly rolled inwards. Height 1.2m.
D. ‘Chat Noir’
A classic, widely available semi-cactus form with huge (15cm across), deep red velvety flowers. Height 1.1m.
D. ‘Honka Red’
Exquisite, star-shaped, bright red flowers with clear yellow eyes. Fab as a cut flower. Height 60cm.
D. ‘Verrones Obsidian’
Another star form with deep red, almost black petals with a golden yellow centre. Great in a pot or front of border, but don’t crowd it out. Height 60cm.
D. ‘Moor Place’
Ball dahlia with the most intricate and perfect petal arrangement. Deep purple colour. Tall too, so appears to float over grasses and perennials. Height 1.2m.
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D. ‘Wizard of Oz’
Soft pink pompom shapes held high above green foliage. These work better in softer-colour borders mixed in with whites, blues and purples. Height 80cm.
D. ‘David Howard’
Much loved miniature, a decorative type with burnt orange flowers and dark foliage. Height 1m.
D. ‘Twynings After Eight’
A strong-growing, simple, open form with white flowers that carry a pink veining and yellow centre. The dark foliage sets them off to perfection. Height 75cm.
D. White Swan
Decorative dahlia with full flowers, creamy on the inside and pure white at the end of the petals. Dark green foliage. Height 1m.
