Click picture for link to instructions on pruning and dead-heading hydrangeas. Hydrangeas need moist, well-drained soil for optimal growth. The pH level of the soil will determine the color of the hydrangea blooms. Acidic soils typically produce blue flowers and neutral to alkaline soils result in pink flowers. Adding coffee grounds or other organic material to your hydrangea's soil will reduce the pH level and make aluminum more available to the plant, resulting in more blue blooms.