Dahlias give you five months. They flower from the end of June until the first frosts stop them, long after most of the summer garden has given up, and a tuber planted in May is in flower by July and still going strong in October. We pick every tuber by hand, the same stock our own show plantings come from.
Where Do Dahlias Come From
Mexico, and it shows. The dahlia grew up on volcanic hillsides, in ground that held moisture without ever sitting wet, with sun all day and shelter from the wind, and the closer you get to that in your own garden the better they will do. Almost any soil will grow them. A little extra care simply produces noticeably better plants.
When Should You Plant Dahlia Tubers
Under glass from March, or outside when the frosts are done. There is no rush to plant, because once tubers wake up, about four weeks from planting, they shoot very quickly, and a May planting all but catches an April one that has sat sulking in cold soil. A greenhouse, cold frame or porch will start them early. The border can wait for the last frost to pass.
How Do You Harden Them Off
Gently, and over a week or ten days. Started plants go first to a sheltered location with some protection from wind and sun until they become acclimatised, come back inside overnight if the temperature is heading below 10°C, and want a close eye kept on them for any sign of stress, because wilted or yellow leaves mean things are moving too quickly. If that happens, bring them in and begin again. Sturdy stems and no wilting means they are ready.
How Deep And How Far Apart
Deeper than you might think. Ten to fifteen centimetres is right (4 to 6in), the tuber laid on its side with the eye facing upward, so the crown sits below the reach of a late frost and the roots feed where the ground stays damp after the surface has gone dusty. Straighter, stronger stems follow. Rake a little bone meal in as you go.
Dahlias need room to breathe. A tall variety wants about 90cm of its own ground, and it will use every centimetre of it by August, when what looked absurdly generous at planting has closed completely.
The mediums take 60cm and the dwarfs 30cm. Crowd any of them and you grow poles instead of bushes, tall thin plants that spend the summer fighting for light and flower as though they resent it. Space is where the show comes from.
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Do Dahlias Need Full Sun
Full sun or light partial shade, and the arithmetic is simple: more sunshine equals more flowers. Deep shade is the one position they will not forgive. In a border, set the taller varieties where the surrounding planting cannot overtake them as summer fills in, and keep the short bedders at the front where the light reaches them.
What Soil Do Dahlias Like
Rich and free draining, in that order of effort. Dahlias are heavy feeders, so work plenty of garden compost in a week or so ahead of planting and let the ground settle, because the whole five month performance is built out of what the roots can find. Cold wet ground is the dahlia’s nemesis. Get the drainage right and almost everything else forgives you.
Should You Stake Your Dahlias
The tall ones, yes, and at planting time rather than later. A cane pushed in beside a grown plant goes straight through the tuber you can no longer see, where one set at planting is threaded through by the roots and never touches it. Cut the canes about 30cm shorter than the plant’s final height and they vanish into the foliage by August. The dwarf and bedding varieties hold themselves up.
Should You Pinch Out The Tips
Yes, once, about a month after planting. When the main stem is somewhere near knee height, take out the growing tip just above a pair of leaves, and the plant answers with side shoots all the way down and twice the flowering stems by July. It feels brutal and it works. One pinch is the difference between a pole and a bush.
What Is Debudding And Should You Bother
Only if you are after size. Every dahlia stem finishes in a cluster of three buds, and taking out the two smaller outer ones sends the whole stem’s effort into the centre bloom, which is how the dinner plate photographs you see are actually grown. Left alone, all three open together and half bury one another in the leaves. For the garden it is optional. For the vase it is the whole trick.
How Do You Get More Flowers
Deadhead without mercy. One spent bloom left to set seed tells the plant its season’s work is done, where a stem cut back to a leaf joint every few days keeps it building buds right up until the frosts, so the habit alone separates a good display from a great one. Feeding is the other half. Once growth is properly away, a high potash liquid feed every fortnight keeps the buds coming, and ordinary tomato feed does the job perfectly. Hold the nitrogen back in midsummer though, or you will grow leaves at the expense of flowers.
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Can You Grow Dahlias In Pots
Yes, and the Gallery series was bred for exactly this. Don’t forget to water your pots, bulbs draw a lot of moisture on their push to flowering, and a dahlia in full flower will drink every single day of a warm week, which is the one real rule of container growing. Tomato feed and ruthless deadheading do the rest. From June to the frosts the pot on the doorstep carries the whole performance.
Can Dahlias Stay In The Ground Over Winter
In the right garden, yes, and it is always a gamble. Their big enemy is a cold wet winter, the wet more than the cold, so tubers planted a full 15cm deep in well drained soil, in a sheltered spot, can be left under a thick covering of mulch and will come through most years. Put the mulch on after the first frosts, never onto sodden ground. If your soil lies wet, do not gamble at all.
How Do You Lift And Store The Tubers
Lift after the first frost has blackened the foliage at the tips, because the frost helps seal the tuber. Cut the stems back to about 12cm, dig each plant out whole taking off what soil comes freely, and stand the clumps upside down somewhere airy for a fortnight so the hollow stems drain dry.
Then the tidy up. Remove the last of the soil, cut the stems down to 2cm, trim the roots to a neat cluster and box the tubers somewhere dry and frost free until spring, checking now and then for any that are softening. They must not get a sniff of frost, as an earlier generation of this family used to put it. Damage never shows until a stored tuber tries to grow in April and quietly turns to mush instead.
What Can Go Wrong With Dahlias
Remarkably little that cannot be headed off. Slugs adore the young shoots, so guard the crowns from the day they go in the ground; earwigs lodge in the open blooms in late summer and shake out harmlessly; mildew turns up in a dry August and regular watering largely keeps it away. The one to take seriously is virus, which shows as mottled, puckered leaves on a stunted plant, and has no cure in the garden. Prevention is the whole game. It is exactly why every tuber here is raised from certified virus free stock.
Which Tall Dahlias Should You Choose
Start with the three everyone asks about. Café au Lait is the giant creamy one the wedding trade fell for, its flowers merging to soft pink at the middle; Arabian Night glows the deepest maroon in the border; and Bishop of Oxford sets coppery orange flowers over that purple tinted bishop foliage, a plant with a sheen on it. All three want a cane and the back row. All three repay it.
Which Dahlias For The Middle Of The Border
The medium bedders do the steady work. Bishop of Llandaff is the famous one, fiery red over foliage so dark it reads black, and a century in gardens has not dated it; Jennifer Mary Ellen carries lavender purple flowers deepening to maroon at the heart; and Bishop of York answers Llandaff in golden yellow over the same bronze leaves. Sixty centimetres apart, and by July they close ranks into a border of their own.
Which Dahlias For Pots And The Front Row
The Gallery series, almost regardless of colour. These are proper decorative dahlias scaled down, most of them to about 35cm, flowering more or less continuously from June, bred exactly for pots, window boxes and the front of the border. Alstergruss is flame orange and outstanding for cutting; Art Nouveau is rosy purple with silvered tips; Art Fair keeps it calm in creamy white. No canes, no pinching, no fuss.
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What To Plant With Dahlias
The plants that peak with them. Gladioli send their spikes up through the dahlias’ first July flush and cut just as well for the house; canna brings the same big leaved tropical weight to the back of the group; crocosmia threads arching scarlet through the front and picks up every warm tone the dahlias throw out. All of them go into the ground in the same spring fortnight as the tubers. One weekend of planting, one border that carries you until the frosts.
