Hydrangeas are very impressive plants, growing up to six feet tall and spreading just as wide. Their blooms are huge, round bouquets of florets that come in colors from light pink to rich blue. Blue hydrangeas and pink hydrangeas are actually the same plant. It all depends on the minerals that are present in the soil as to whether the blooms will be one color or another. To have blue hydrangeas, adjustments can be made when planting to ensure they keep that color.
Select an area in the landscape approximately 4 x 4 feet to allow the hydrangea to grow to maturity without needing to be trimmed. The area should receive diffused light.
Avoid planting blue hydrangeas near cement or concrete, as the lime in these will turn the soil alkaline and can change the color of the hydrangeas.
Plant hydrangeas in late spring or fall. Avoid planting in the heat of summer, if possible.
Dig a hole around three times as big as the root ball and deep enough so that the entire root ball will be covered when the hole is backfilled.
Remove the hydrangea from its pot and loosen the roots by hand. Place the hydrangea in the hole at the same depth as it was when growing in the pot.
Test the soil with the pH kit to see if it is acidic with a pH below 5.5. Lower the pH of the soil, if necessary, by adding used coffee grounds.
Backfill the hole with the soil, ensuring that the soil level is not too high around the plant. Firm the soil into place.
Add a solution of one tsp. of aluminum sulfate per gallon of water to the soil to help the hydrangea to bloom blue.
Ensure that the water you use to irrigate the hydrangeas has a pH higher than 5.5.
Feed the hydrangeas with a fertilizer that is high in potassium and low in phosphorus, such as a 25/5/30 combination. Avoid using superphosphates and bone meal when growing blue hydrangeas.