Extreme Temperatures and Sun Scorch
While sunflowers thrive in heat, sudden temperature spikes above 95°F can stress young plants—causing leaf curl, halted growth, or scorched foliage. I recall one blistering week where my sunflowers froze in place, refusing to open even one bud! Similarly, brief cold snaps can nip seedlings or delay flowering.
To buffer extremes, use shade cloth during the hottest afternoon hours in scorching climates, and cover tender seedlings with row covers on cool nights. Proper mulching and consistent watering also help regulate root-zone temperatures, ensuring your sunflowers stay comfortable enough to produce those huge, nectar-rich discs.