Q: I heard you talk about a different hydrangea than the normal French mop head. What is it?
A: Hydrangea macrophylla, also called bigleaf, mopheads or French hydrangea, has either pink or blue flowers. Flower color is determined indirectly by the soil pH, which affects the availability of aluminum in the soil. In acid soils the flowers will be blue; in alkaline soils the flowers will be pink. Aluminum is available to the plant in acid soils. Research has determined the actual mechanism of color variation is due to the presence or absence of aluminum compounds in the flowers. For blue flowers, maintain a soil pH between 5 and 5.5. Apply aluminum sulfate or sulfur to reduce the pH to this range when you see new growth emerging in April. For pink flowers, maintain a soil pH of 6 or more by liming your soil. “Lace cap” was the other type of hydrangea you heard me discuss. The “lacecaps” have a center of fertile, relatively non-showy flowers and an outer ring of showy, sterile flowers, which together form a pinwheel effect. Hydrangea requires shade (either continuous shade or morning sun and afternoon shade), moist, but not wet soils, and cool winters. After plants are well established, French hydrangea is moderately drought tolerant and moderately salt tolerant. For more complete information on growing hydrangeas, please check out this University of Florida publication: http://edis.ifas.ufl.edu/ep330