Can I mix lime in the dirt when I plant my hydrangeas to keep them pink and red?

Great question! I do not recommend adding lime into the soil, even though that will increase the soil pH and therefore encourage alkaline-induced red blooms. The problem is that lime is available in various formulas so getting the correct balance may be tricky. I recommend you watch this video all about soil amendments and fertilizer that goes over how to change your bloom color in detail.