Dahlias and Geraniums Not Blooming in Heat: Nitrogen, Temperature, and Photoperiod Effects

Gardener's dahlias and geraniums in same pot stopped flowering. Used high-nitrogen fertilizer. Asks if that's the problem for dahlias too.

Deep Dive (The Long Island Gardener)

2010 summer heat waves (80-90°F) are major factor. High nitrogen promotes foliage over flowers, but heat is stronger force.

• Heat damages thylakoids (photosynthesis), reduces "stay green" trait.
• Geraniums set buds 45-80°F; optimum 70-72°F.
• Dahlias: short days induce flowering; need 10-12 hr days for tuber formation, but 12+ hr for flower development. Heat delays bud set.
• Plants were forced into bloom by growers; now confused.

Prediction

As days shorten and cool, both will rebloom. Don't overfertilize; use organic fertilizer, quality potting soil, add earthworms. Pinch spent blooms. Be patient.