Q: Last year my daughter gave me a hydrangea that had a gorgeous deep mauve bloom. I planted it and it has grown very well. But I was surprised when the bloom opened and is now blue. What do I need to do to have the deep mauve blossoms?

A: The gift hydrangea was grown in a greenhouse where the pot’s soil pH could be precisely manipulated to influence the bloom color. Once you planted it outdoors, our naturally acidic soil caused the bloom to revert to blue. Apply a cup of lime around the plant now and in August to raise soil pH. The easiest way to get purple blooms is to start with a variety that likes to be pink naturally. I have suggestions for how to do it at bit.ly/purplehydrangea