Dahlias – from garden outcast to garden darling

Dahlias have certainly come full circle after falling from grace from the 60’s - 90’s during the rise of formal and then minimalistic garden design. There was no room in the garden for these bright, exuberant blooms.

Over the last decade they have crept back into fashion with social media, in particular Instagram and the rise of home flower farmers bringing the gorgeous blooms to our attention causing their popularity to skyrocket over the last view years. Dahlias have grown so popular they have been compared to Holland’s ‘Tulipmania’ in the 1700’s.

They certainly deserve their time in the sun. Dahlias have wonderful range of shapes, sizes and colours. From dinner plate sized in vibrant hues through to tiny pom poms in delicate pastel, there is something for everyone’s taste. They repeat bloom from mid-summer through to mid-autumn. They are straight-forward to care for and they look stunning, in the garden, as cut flowers, dried on a wreath or in a display.

You should consider the space in your garden when choosing your varieties. The dinner plate varieties take up quite a bit of space and the weight of the sizeable blooms, have a tendency to flop if not securely staked. The cactus and decorative varieties while smaller in flower can also take up a lot of real estate in your border and they can be quite tall. If the position is not sheltered from wind, staking is highly recommended. If space is limited or you’re planting in pots consider the pompom, gallery, anemone or collarette varieties that tend to be smaller in plant size and bloom size.

A dahlia grows from a tuber in the ground. It dies down completely in winter and resprouts in spring. To avoid the tuber rotting if your soil is heavy and wet over winter, it is highly recommended that you lift the tuber after it dies down and you store it in a cool, frost free spot over winter. Replant in the spring. If the tuber is in well drained soil or a raised bed, you can leave it in place but ensure it is well protected from frosts with a thick layer of compost or mulch.

Lifting the dahlia tuber does give you the opportunity to inspect for damage, or to divide the tuber into multiple new plants. You simply need to ensure that there is an ‘eye’ or sprout on the section of tuber you are going to divide off. There are usually multiple eyes on a tuber. This is a great way to increase the number of plants you have or to share different varieties between friends. Alternatively, you can purchase specific named dahlia varieties from a garden centre in mid winter.

How to get the best performance out of your dahlias? Feed them well with a bulb food when they are beginning to sprout and after they finish flowering and start to die down. This will give the plant a boost to start its season and to help the plant store food in its tuber at the end of the season. Once it is in full growth, feed with a fertiliser for flowers such as rose fertiliser or one with a high balanced nitrogen and potassium levels on the NPK rating. This is to support plenty of blooms. Remember to deadhead the finished blooms to encourage the plant to flower again during the season.

In terms of pests and diseases, there are a few to keep your eye out for. Regularly checking in on your dahlias is key to putting a stop to any problems before they become a real issue. As soon as you see the first sign- do something about it! Physically remove the insect or affected part of the plant to slow the spread or stop it completely. Follow up with an appropriate spray.

Slugs and snails will make fast work of the new shoots so ensure you spread some bait around to protect them in early spring. If you head out at night with a torch you will catch them in the act!

If the petals are ragged, earwigs are probably to blame or if there are holes in the centre of the dahlia and petals but no slime trails, take a closer look and you’ll spot a very hungry caterpillar munching away. Removal is the easiest control for caterpillars, otherwise apply a spray that controls caterpillars. Earwigs are harder to control, they are nocturnal and they like to hide so remove any potential hiding places and provide one with a damp rolled up newpaper tied with string that you can get rid of them from daily .

Mites and thrips can be an issue at times, thrips cause a light flecking on the petals, mites are hard to see but cause a mottling on the leaves. Grosafe BioNeem or Groventive will provide control for these.

The disease that can be a common occurence on dahlia leaves, especially in warm humid weather is powdery mildew. Silver powdery blotches on the leaf surface that can spread quickly if left untreated. Removal of the affected leaves at first sight is the best control/prevention. If it has started to spread, Grosafe Enspray 99 is effective at smothering spores on contact so thoroughly spray the foliage. You will need to repeat if it appears again. Good airflow through the plant is helpful in prevention so you may need to thin out some foliage if the plant is particularly crowded. Watering the soil and not the foliage will also help prevent it.

Dahlias are a wonderful addition to your garden, with plenty of colours, shapes and sizes to choose from. Whether they are colour for the garden or for picking to enjoy inside, they will bring you much pleasure.

Written for Gubba by Kelly Jean Reyland from Garden Advice NZ (www.gardenadvice.co.nz)