Hydrangeas will thrive in most soil types. However, the pH of the soil will change the colour of the flowers of some varieties. Some plants that usually offer pink flowers will appear blue if the soil is acidic. You can change the colour to blue by feeding with a fertiliser low in phosphorous and high in potassium. Alternatively, you can grow your plant in an ericaceous compost in a pot to keep it blue.
To change a plant from blue to pink is trickier. You will need to raise the pH by adding dolomitic lime. It's quite common for a plant to produce a few different coloured flowers on one plant in the first year of growth. Few gardeners concern themselves with trying to change the flower colour – but it is interesting to know why plants may vary.
A moist, well-drained soil in a position of dappled shaded is ideal. Avoid south-facing positions, especially if the soil if very dry. For a north-facing wall, grow the reliable climber Hydrangea anomala subsp. petiolaris.
Hydrangeas are best planted in spring or autumn. Never plant them deeper than they were in their original containers.
When planting climbers, train them up the wall onto galvanised wires. After a season of growth they'll make their own way as they have aerial roots.
Take softwood cuttings in spring and early summer. In the morning look for young, non-flowering shoots that have three sets of leaves. For best results prepare cutting material straight away. Alternatively, keep them in a plastic bag in a cool shed.
Remove the two sets of lower leaves and shorten the stem of the cutting. Cut just below a node. Insert the cuttings into a pot of cutting compost. More than one cutting can be placed in a pot as long as the leaves don’t touch. Water in and cover with a clear plastic bag. Ideally keep them in an unheated greenhouse.
Once you see clear signs of growth pot on plants, keeping them in a shady spot.
Hydrangeas are very easy to grow and there are few pests and diseases that hinder them. Container-grown specimens may be prone to vine weevil attack and some plants will be damaged by frost. To avoid frost damage, leave the faded flowerheads on the plant and prune at the correct time.
As there's such a wide range of hydrangeas, it's important to note that one pruning technique does not suit all. Climbing types are pruned in summer after flowering. Others are pruning in spring or late autumn.
The faded blooms of hydrangeas are attractive in the winter months. Ideally, leave them on the plant over winter as on some types this protects the plant from frost damage.
When pruning mophead types it's vital that you don’t deadhead below the top set of plump buds that are forming under the flower head. This is where the new flowers will form. Cut plants back to just above these fat buds.
Lacecap hydrangeas are tough so can stand deadheading in autumn. Both mophead and lacecap types will benefit if some of the oldest stems are cut back completely at the base of the plant. This will encourage new stems and should be done in February.
Hydrangea paniculata and Hydrangea arborescens flower on the current season’s growth so they should be pruned in spring. Prune old stems back to four buds. If you avoid pruning hydrangeas the flowers will soon get smaller and smaller.