Why Dahlias Stop Flowering: 3 Common Causes and Fixes
August is a peak time for dahlias, as these showy blooms burst with color and dazzle with their intricate petal arrangements. But, in the current heatwaves we’re experiencing, these perennials can struggle to put on such a spectacular display. Luckily, if your dahlias have stopped flowering, it’s easy enough to fix before fall.
Growing dahlias takes patience, perseverance, and careful management if you want to get a showstopping display. The scorching temperatures and lack of rainfall this summer are likely to be the most common cause behind a lack of blooms. Forgetting to deadhead and nutrient deficiencies in soil can also cause a lack of flowering – that’s why it’s a good idea to always have some gardening snips to hand (like these Fiskars garden snips on Amazon).
The good news is there’s still plenty of time left in the growing season to revitalize your dahlias and get them flowering once again. Here, with insights from an expert, we talk through the top three reasons why dahlias stop flowering and how to fix it.
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1. Heat Stress
(Image credit: Getty Images/Jacky Parker Photography)
The reason dahlias stop flowering prematurely is because they’re experiencing stress in their growing environment. During hot summer weather, heat stress is often the culprit.
‘Dahlias thrive in the temperature range between 60-80°F. Extreme August heat spikes above this range can cause plants to go temporarily dormant and stop producing new flower buds,’ explains Plantum plant expert, Marina Prokaten.
Other symptoms of heat stress include leaf scorch, wilting, and pest damage, due to being more vulnerable.
Alongside improper watering, this can cause a decline and the premature death of your dahlias.
‘During hot, dry periods when the soil dries out quickly, dahlias need a deep soak 2-3 times a week. Always water deeply at the base of the plant – overhead watering wets the foliage, which rots developing buds, damages heavy blooms, and drastically increases the risk of flower-stopping fungal diseases,’ Marina describes.
By keeping your plants hydrated and using a shade cloth (like this from Amazon) during a heatwave, you can combat heat stress and nurture your dahlia back to healthy blooming.
Marina Prokaten is a resident plant expert for the Plantum app, which helps users identify plant species, diagnose their conditions, and get specific care advice. She has three years of experience consulting on botany-related topics for Plantum.
2. Lack of Deadheading
(Image credit: Future)
One of the best ways to get non-stop flowers from your dahlias is by keeping on top of pruning and deadheading.
Once pollinated, dahlias form seed pods that need to be removed to encourage more flowers. They can be easy to miss, as they look similar to flower buds, yet are more cone-shaped. If you neglect removing them, it signals to the plant the flowering season is ending and it begins slowing down.
The best thing to do is remove spent blooms as soon as you spot them, following the stem down to the next set of leaves and making a clean cut. These Felco F2 pruning shears from Lowe’s would work well for dahlias.
You can also pinch out dahlias to encourage a more prolific display and disbud dahlias to get longer stems with bigger flowerheads.
Pruning dahlias like this will redirect the plant’s energy into putting out more blooms before the summer season ends.
Just take care to avoid pruning mistakes when trimming these perennials, as you could sabotage your late-summer display by accidentally removing buds.
3. Nutrient Deficiency
(Image credit: Clive Nichols/Getty Images)
Dahlias are very hungry plants and when they’re flowering, they use up a lot of energy and nutrients in the soil. If they start to slow down, it might just be they have a nutrient deficiency and are struggling to put out blooms.
Likewise, if you have been fertilizing your dahlias, Marina warns you could be using the wrong type:
‘Using high-nitrogen plant food promotes lush foliage instead of flowers. To keep buds forming through August, feed your flowers with a low-nitrogen liquid fertilizer every 3 -4 weeks from mid-summer to early autumn,’ she advises.
Look for fertilizers with an NPK ratio higher in phosphorus and potassium, as this supports blooming. This TPS dahlia fertilizer from Amazon is a good choice.
You can also use this Amazon soil test kit to determine which essential plant nutrients are lacking in your dahlia’s soil and amend as needed.
What to Shop
These pruning snips are ideal for tending to dahlias, with a micro-tip blade to remove spent blooms.
Terracotta Watering Spikes
These terracotta watering spikes release water to surrounding soil gradually, ideal for keeping dahlias hydrated in hot weather.
This liquid fertilizer is a special formula to support dahlia growth and blooming. Dilute with water to apply.
Marina notes to also look out for summer garden pests and diseases on your dahlias:
‘Aphids attack delicate young growth and floral buds, draining energy and preventing buds from opening. Use neem oil (from Walmart) or insecticidal soap to tackle the issue early on.
‘Powdery mildew typically strikes in late summer, covering foliage in a white coating and depriving the plant of the energy required to set flowers. Prevent powdery mildew by maintaining adequate plant spacing for airflow, keeping foliage dry when watering,’ she says.
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