An Ode to Dahlias

Becky_Alton
5 September 2022

Dahlias are originally from Mexico and it is the national flower for the country. Their bright, showy rainbow colours and numerous sizes & shapes were introduced into the UK around 1798. Dahlias flower from July up to October - usually a little later here in Cornwall due to the mild autumns.

So much beauty

There are types that will suit every need and they are classified according to the size/character of the flowers. Some of the sections are as follows; Peony flowered, single & collarettes flowered, Anemone centred, giant flowered, Cactus flowered, pompon flowered, and orchid flowered, to name a few.

At Heligan, every year we invite the Cornish Dahlia society to plant up nearly 1500 Dahlias with a showstopping array of blooms within the garden. These flowers have a strong connection with the Victorians, who felt that dahlias symbolise devotion and love, so they were used widely for wedding celebrations and bouquets.

How to grow your own

Dahlias will grow well in practically any soil type and with little attention other than staking and supporting, and the addition of compost or well-rotted manure every so often will help with even better results. They love a sunny spot but need a bit of shelter from strong winds. Shady spots should be avoided as this will make the plant grow tall and weak.

Dahlias aren’t deep rooting plants so they will need supports. The best time to add supports are straight after you plant them, placing stakes in the corner of the dahlia beds and lying metal fencing mesh with larger holes which you can buy from hardware stores, over the bed around 1-2 ft off the ground. This will help the blooms with support and they will grow through the mesh. You can always tie the plants individually after they start growing taller. Dahlias included in borders or dwarf varieties probably won’t need as much attention, but you can always tie them in to a few canes.

When to plant

If like me you don’t have the biggest area to grow in, you can always use pots. Make sure the pots are big enough to home the tuber so they won’t become pot bound once the dahlias start to grow, and fill them up with some peat free compost.

Dahlias must be planted in the ground after the last frost. This will be different all over the UK so ignore the calendar and get watching the weather reports as closely as possible. This also depends on the soil type you have as some soils will take a lot longer to warm up as well as the site you are looking to plant them in. If once you have planted them out an unexpected frost is on the horizon, cardboard, straw or even an upturned pot can help protect the tuber in the soil from the cold frost.

Protecting from pests

Dahlias are susceptible to pests in the early stages of growing when the foliage is tender – things like earwigs, slugs and snails. I’ve found having my dahlias in pots has prevented these pests at the beginning of growing ensuring the dahlia has a good head start. Deterrents such as coffee grounds, crushed eggshell and beer traps can help in an organic attempt. Tidy garden beds can help with any hiding places for pests as well as irrigation methods such as a soaker hose. This will wet the soil around the plant keeping the leaves dry which will help deter slugs. Nematodes that you water in can help with small areas but sometimes the most effective way is to hand pick through your beds.

When the flowers are blooming, earwigs like to eat the petals but having earwigs present isn’t bad as they also keep control of aphids and mites, so I try to help with the habitat. Earwigs like dark, moist places to hide so keeping your beds clear of any groundcover will help. To help lure earwigs away from your blooms I tend to put a small terracotta pot upside down on a stick which I’ve stuck into the ground, away from my Dahlias, stuffed with straw.

What to do at the end of the season?

After months of blooms that have created dozens of posies for friends and family what do you do with you Dahlias once they start to fade? Dahlias will not tolerate freezing temperatures, so wait until the plant has died back and when this happens, dig them up and bring the tubers indoors. You can cut back after the first frost as this will turn the stems and foliage black. Leaving the tubers in a little longer, maybe a few days after the frost, can help toughen the tubers skin.

Once you’ve removed from the ground, make sure you label the tubers and check that they are healthy. Let them dry out for a few days out of direct sunlight. Some tubers maybe large enough to divide meaning you will have more plant for next year. Bonus! If dividing your tubers, each one must include an “eye” as this is where the first growth comes from. This takes practice so you could wait until spring as some “eyes” may start to grow.

Keeping them nice and safe until spring

Once they have dried out, store them over winter in a place which depends on how much room you have. I tend to pot all my Dahlia tubers back up in fresh compost and keep them in my shed or greenhouse. This means they are protected from frost also; so I can keep an eye on them. You can also store them in boxes in other growing mix such as vermiculite or black bin bags, but ensure they have ventilation.

Always check your tubers throughout the winter periods, making sure they are not too wet or too dry. When spring arrives, you can thoroughly go through your saved tubers only keeping the best ones, or if they are in pots start watering a little more and look out for growth.

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