Dahlias

Dahlias – not just for your granny!

Dahlias are back! They add magnificent splashes of colour to your balcony or garden and are also fabulous as cut flowers. So in the last few years they’ve revived as popular summer flowers instead of being thought of as old hat. They bloom from midsummer and can go on until the end of November. Tall and elegant, or small and a bit more retiring, they wow us with their vibrant colours. These range across reds, purples, pinks, yellows, orange, peach and cool white.

The dahlia is the national flower of Mexico. Mexicans (including the grannies) love a fiesta and the zingy, celebratory colours of these flowers are in synch with this.

Forget banana bread. While we’re stuck in Lockdown3 think ahead to summer sun with oodles of fresh air and creative exercise. Beat those lockdown blues by planning your summer garden display now.

Our top dahlia combos

Dahlia Collerette Red/White

Ornate and reminiscent of papel picado, the Mexican art of paper cutting. These flowers have an outer ring of flat petals surrounding a smaller inner ring often in contrasting colours. Their central stamens are a cheerful buttercup yellow and they’ll grow up to 1m tall.

Dahlia Cactus Orange/Yellow/White

Starburst dahlias with fat and tactile heads of fine petals. Each flower is a vibrant orange or yellow or a contrasting cool and calming white.

Dahlia Pompon Pink/Purple

These are large spherical flowerheads with a geometric texture and pattern. Their colours range from lively purple and magenta pink to pale rose.

Dahlia Combi Violet/White

These double flowers are reminiscent of sea anemones. A profusion of deep violet, white and striped and speckled burgundy.

How do I grow them?

Dahlias have tubers which look similar to bulbs and perform the same essential task of storing nutrients. They need an open sunny site with lots of water and a rich, free-draining growing medium. Plant them around April and May after the danger of frosts has passed.

To plant:
  • If you’re planting directly into the ground, you’ll need a hole about 30cm deep x 30cm square for each plant. Scatter about 15cm of compost into the bottom of the hole. On very heavy clay, add a sprinkling of grit too.
  • Place the tuber in the hole and backfill with compost. Water in well. Plant your dahlias about 30cm apart.
  • Tall varieties will be helped by a bamboo cane next to them to provide support
Pots:

In pots, you’ll need a pot about 30cm in diameter for one plant.

5 tips for keeping them in prime condition

  • These are hungry plants (all that celebrating!), so once a fortnight feed them with a liquid balanced feed
  • They’re also thirsty. In very dry weather, it’s a good idea to water them well once a week.
  • Tie them in to the stake every couple of weeks
  • Pick flowers or deadhead from the bottom of the flowering stem to encourage new flowers
  • Slugs and snails will be tempted to nibble so it’s as well to provide some protection

Overwintering

Glamorous and beautiful, dahlias are also tender and protest at frost. But with a bit of attention they’ll come through the winter and pop up again next spring.

Traditionally the tubers have been lifted from the ground and stored in a frost-free place over winter. But garden writer and broadcaster James Wong says those days are over – dahlias are tougher than we’ve been led to believe.

How do I coax them through?

Once frost has blackened the foliage, cut it back to leave about 10cm of stem. Cover them in at least 15cm of organic mulch, such as bark, straw, leaf mould or compost. This will insulate them from the cold. Mulching has the added benefit of discouraging weeds, helping to control moisture loss from the soil, and gradually breaking down to improve the structure of the soil and add essential nutrients.

Lifting:

Step 1

If you do decide to uproot your dahlia tubers, cut the stems back as you would if leaving them in the ground. They need to be stored somewhere frost-free but cool, dark and dry like a shed. It’s important to keep them at a low temperature – you’re trying to mimic their natural dormancy cycle. Warmth may make them sprout and they’ll go into shock if it’s still a bit chilly when you plant them out again in spring.

Step 2

Carefully dig or lift the tubers out of the soil and gently brush most of the soil off. If you’re worried about damaging them, just gently shake off as much as you can. Take to your chosen cool location. Place them upside down so that any moisture still in their hollow stems can drain out.

Step 3

Allow any soil still clinging to them to dry out well. Then slide them into a brown paper bag, wrap in newspaper or place in a cardboard box until late spring when there’s no chance of frost. If you feel like splashing out, nestling them in sand in a tray will also help keep them dry.

What should I do if they’re in pots?

  • Compost in pots often gets colder than soil in the ground – there’s a greater surface area exposed to the cold and less of it to provide insulation. So the plants are at greater risk.
  • The best way to protect your tubers is to cut the foliage back and put the pots in a frost-free place. But if you can’t, all is not lost! There are other things you can try.
  • Wrap them in layers of horticultural fleece. Move the pots against a sheltered house wall which will provide some warmth, and huddle them together so that they provide insulation for each other like a mini colony (or ‘waddle’ – yes, really) of penguins.
  • To improve drainage and reduce the risk of waterlogged compost, put pots up on pot feet.
  • Dahlias give you a lot of bang for your buck. In the right conditions and in the right combination, they’ll flower from June until early December. We think they’re the stars of the late summer garden.

Other related blogs you may find of interest

https://www.pashleymanorgardens.com/events/dahlia-days/

Written by Andy Williams

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