Macrophylla hydrangeas, better known as the blue and pink mophead and lacecap hydrangeas, are the most popular type of this versatile shrub. The lacecaps bear a ring of flowers around florets in the centre; the mophead hydrangea has large flowers resembling pom-poms. With the right location for morning sun and afternoon shade, well-drained soil and proper watering, hydrangea macrophylla can enhance your yard in late summer with its colourful blooms and fine foliage.
All hydrangeas thrive in morning sun and afternoon shade, especially hydrangea macrophylla. In northern U.S. climates, these shrubs can tolerate full-day sun. In southern U.S. climates, they cannot withstand afternoon sun. Wherever you live, your hydrangea will not do well in deep shade. Do not plant near shade trees.
Most hydrangeas will grow to 4 by 4 feet in size, so choose your location accordingly. Plant in soil that is rich, organic and drains well. Following the manufacturer's instructions, use a soil test kit to check your soil's pH level. Hydrangea macrophylla does best in acidic soil. Using a trowel or small shovel, dig a hole that's twice as wide and just as deep as your hydrangea's root-ball. It's best to plant in spring or fall; avoid summer heat. Fill the hole partway, then water; finish filling, water again and add mulch.
Once planted, add mulch around your hydrangea bush so it retains water but prevents weeds. Water your hydrangea macrophylla well, especially when it's young, so it doesn't dry out during heat. Add compost and peat moss to the soil at the base of the plant; fertilise in spring and again in late summer. (Another choice is to use a slow-release, balanced fertiliser just once in early summer.)
Trim off old flowers and broken branches in the spring. In late summer, after blooming, prune above the top buds. For larger flower clusters, reduce by half the number of stems to thin your plant.
You can lower the soil's pH level, if necessary, by adding aluminium sulphate every two weeks. Be sure your hydrangea gets plenty of moisture to sustain it during droughts. Transplant hydrangea macrophylla only when they are dormant, and water thoroughly once. For the first two summers after transplanting, your hydrangea will need plenty of long, deep waterings. To change the blossom colour, alter the soil's acidity. Adding aluminium sulphate makes the soil more acidic. For blue flowers, the pH level should be between 5 and 5.5. Raise it to 6 for pink flowers by adding lime, which makes the soil alkaline.
Don't let your hydrangea stand in soggy ground that does not drain well. This is where the compost and peat moss can help.