It’s officially dahlia season, and for most varieties, the wait for those first displays is finally over. Many of us will be left wondering the same thing, though: Why aren’t my dahlias blooming?
It’s a common problem, sadly – and even if you’ve mastered the art of growing dahlias in pots or garden borders, no-show blooms happen to the best of us. It can come down to the wrong fertiliser, soil, or watering schedule, to name a few culprits.
I checked in with plant experts to help you figure out why your dahlias aren’t blooming. Below, you’ll find the most common causes.
1. Too much fertiliser
Feeding your dahlias is important, but overfeeding can do more harm than good – and it could be why your dahlias aren’t blooming. More specifically, too much nitrogen in a fertiliser can be a problem.
‘While nitrogen helps leaves grow, too much of it can stop the plant from producing flowers,’ explains Julian Palphramand, head of plants at British Garden Centres. ‘It’s best to use a feed that isn’t too heavy on nitrogen, so check the ingredients when buying from your local garden centre.’
A fertiliser like Vitax Dahlia Feed, £8.99 from Amazon is designed to promote strong growth and plenty of flowers.
2. Too little sun
Dahlias thrive in the sunshine, and too much shade is actually one of the most common reasons why dahlia leaves turn yellow. It can affect your plant’s flowering potential, too.
‘Dahlias need at least six hours of direct sunlight a day,’ says David Fryer, head of technical at Mr Fothergill’s. ‘If they are planted in too much shade, they will still grow but may not produce flowers.
‘Even in a sunny position, persistent dull weather can delay flowering, but usually, flowers will follow once the sun returns.’
3. Underwatering (or overwatering!)
An incorrect watering schedule can spell disaster for most plants, and dahlias are no exception. Overwatering can cause dahlia tuber rot, but it can also hinder flowering further down the line – and so can underwatering.
‘Dahlias are thirsty plants, so it’s important they get plenty of water, especially during prolonged dry and hot spells,’ says Alex Biggart, brand manager at 123 Flowers.
'Grown in containers, especially terracotta pots, they will dry out quicker. They dislike water-logged soil, so ensure your soil has adequate drainage, too.’
4. The slugs got there first
One of gardening expert Sarah Raven’s two golden rules for growing dahlias is potting them up first so that the plants mature a little before they enter the outside world – but if you planted the tubers outside directly, or bought very young plants, the tender shoots (and flowers-to-be) might have been eaten by slugs.
‘They typically go for the new shoots and flower stems, and damage often isn't noticed until it's too late and the buds are gone,’ explains David from Mr Fothergill’s.
Slugs were the downfall of my dahlias a few years ago, but I found that copper tape (like this copper slug tape, £5.99 from Amazon) kept them at bay when I tried growing them again the following year.
5. You aren't deadheading them enough
You should generally deadhead dahlias to make room for new blooms and prolong their flowering period. If your dahlias aren’t blooming, there simply might not be enough energy and space on the plant. That’s why deadheading is one of the most important ways to keep your dahlias blooming.
‘Sometimes, after an initial flush of flowers, dahlias may stop blooming,’ says David. ‘To ensure a long flowering season, always remove dead flower heads. This prevents the plant from diverting energy into seed production and encourages more blooms instead.’
Just make sure you use a clean, sharp pair of snips, like the Darlac Compact Snips, £13.49 from Amazon.
Dahlias can be sensitive plants, so make sure you aren't making any of the above mistakes. That way, you'll grow your best displays yet.
