I have a customer who wants to bring their hydrangeas back to the blue-ish/purple color they were when we planted them. The customer has been adding soil acidifier, but there's been no change. Would it be a good idea for me to have a soil test done? I am thinking he is not using the correct amount to achieve his goal.
I would definitely recommend a soil test. A soil pH of 5 - 5.5 is needed for hydrangeas to achieve the blue color desired. Depending on what the present soil pH is, more acidifier (aluminum sulfate or sulfur) may be needed than is presently being applied. MSU Extension has self-mailer soil test kits available at most county offices or by ordering through the MSUE bookstore at: http://shop.msu.edu/product_p/bulletin-e3154.htm