Planting hydrangeas is best done in the spring or fall. Spring planting can be one to two months before your average last frost date, depending on the climate of your location. Fall planting should not be delayed beyond October 15th, as this is when temperatures begin to cool below 50 degrees Fahrenheit (10 C). Avoid planting during periods of freezing temperatures and extreme cold spells. The moisture content must also be correct for hydrangea growth; a soil that does not drain well will cause detrimental effects to both plant growth and quality.