Dahlias can stop forming new flower buds during severe August heat, but adjusted watering and pruning can restore blooms before autumn, according to plant experts at Homes & Gardens.
High temperatures combined with dry soil frequently cause dahlias to halt flower production in late summer. Gardeners can restart the blooming cycle before the season ends by addressing heat stress, removing dead flowers and adjusting soil nutrients.
Dahlias are tuberous perennial garden plants widely cultivated for their vibrant late-season displays that typically last until the first frost. Homes & Gardens, a lifestyle and gardening publication, consulted plant specialists to explain why flower growth stalls in August and how growers can intervene.
Managing heat stress and watering
Heat stress is one of the primary reasons dahlias stop flowering prematurely. Plant expert Maryna Prokaten said dahlias grow best in temperatures between 16 and 27 degrees Celsius. When August temperatures exceed that range, plants can enter a temporary state of dormancy and stop setting new flower buds.
Additional signs of heat stress include scorched leaves, wilting and increased vulnerability to pest damage. Prokaten noted that combining heat stress with improper watering can weaken plants and even cause premature death.
During hot and dry periods when soil dries rapidly, gardeners should water dahlias abundantly two to three times each week. Water must be applied directly to the base of the plant rather than from above. Overhead watering wets the foliage, which can cause flower buds to rot and elevates the risk of fungal infections.
Installing shade netting over garden beds during extreme heat waves also protects plants from excessive sunlight, helping lower plant stress and support continued flower production.
Deadheading faded blooms
Failing to remove withered flowers is another common reason dahlias cease blooming. Once a dahlia flower is pollinated, the plant begins developing seed pods. Left unchecked, seed production signals to the plant that its reproductive season is closing, prompting it to slow down flower development.
Gardeners should deadhead spent blooms immediately by making a clean cut directly above the next pair of leaves. This pruning technique redirects energy away from seed creation and back into forming fresh flowers.
Nutrient requirements and disease control
Nutrient deficiencies can also impair flower formation, as dahlias consume substantial energy during their peak growth phase. Slowed growth or a drop in flower count often indicates that the soil lacks key minerals.
Selecting the correct fertilizer is critical for encouraging blossoms. Prokaten explained that fertilizers containing high levels of nitrogen encourage lush leaf growth rather than flower buds. Nitrogen primarily feeds vegetative growth in plants, whereas phosphorus and potassium stimulate root development and flower production.
To maintain bud formation throughout August, Prokaten advised feeding dahlias with a liquid fertilizer low in nitrogen every three to four weeks from mid-summer until early autumn. High-phosphorus and high-potassium formulas should be prioritized, and soil test kits can be used to pinpoint specific nutrient deficits.
Pests and fungal diseases must also be monitored closely in late summer. Aphids can damage young shoots and unopened buds, preventing flowers from expanding properly. Meanwhile, powdery mildew, a common fungal infection, covers leaves in a white powdery residue that deprives the plant of energy needed for flowering. Providing adequate spacing for air circulation between plants and avoiding wet foliage during watering helps prevent powdery mildew outbreaks.
Ukrainian news agency UNIAN previously detailed seven essential steps gardeners should take during August to ensure dahlias remain covered in flowers until the first frosts. Plant specialists highlight August as a decisive month for dahlia development, when routine maintenance determines late-season performance.
