Question: How can I get my hydrangea to change its flower colors?

Answer: Florists’ hydrangeas are botanical oddities, in that their flower color changes with changes in the acidity or alkalinity of their soil. They bloom rich blue in acid soils and bright pink in alkaline soils. Truth is, it’s probably best to accept the color you already get, rather than trying to change them. If you miss in your attempt, you’ll have floral bracts with very muddy brownish colors. For the record, however, you would add agricultural lime to turn an acidic soil to alkaline, and you’d use aluminum sulfate to get plants to bloom blue in alkaline soils. If you’re going to attempt the latter, however, you should also plant them in pure organic matter, including peat moss and bark mulch. For the record, other hydrangeas such as oakleaf and pee gee types have white bracts that are not affected by the soil’s acidity or alkalinity.