Hydrangeas bring big clusters of flowers to gardens where many sun-loving shrubs struggle. They can brighten a partly shaded border, fill a substantial container and remain attractive as their flowers fade in autumn. But they are not all the same plant. A mophead hydrangea and a panicle hydrangea can require completely different pruning, so knowing which one you have is the first job.
Identify your hydrangea before you prune
Mophead and lacecap hydrangeas usually belong to Hydrangea macrophylla, with some similar-looking H. serrata varieties. Their flowers develop mainly from buds carried through winter on older stems. Remove those stems at the wrong time and you can lose a season's display.
Panicle hydrangeas, H. paniculata, make cone-shaped flower clusters and commonly bloom on the current year's new growth. Smooth hydrangeas such as H. arborescens also flower on new growth. They can generally be pruned more decisively in spring.
Check the plant label for its species and mature size. A compact shrub suitable for a pot will behave differently from a vigorous panicle hydrangea capable of filling a large border.
The best position for hydrangeas
Most shrubby hydrangeas prefer moist, fertile soil that drains well. Light shade or morning sun with some afternoon shelter suits many mophead and lacecap varieties. Plants grown in strong sun may need more watering, especially on sandy soil.
Panicle hydrangeas are often more tolerant of sunshine if their roots have sufficient moisture. Very deep shade, however, can reduce flowering. Avoid planting directly beneath large trees where roots compete for water.
A sheltered position helps protect flower buds from late spring frosts. In exposed Lancashire gardens, a warm wall or protected border can be especially useful for the types that carry flowering buds through winter.
When should you plant hydrangeas?
Spring and autumn are reliable planting times when the ground is neither frozen nor saturated. Container-grown plants can be planted at other times if the weather allows, but they require more attention during hot, dry spells.
Before planting, water the pot thoroughly. Prepare a wide hole no deeper than the original rootball and loosen the surrounding soil. Incorporate well-rotted organic matter if the ground is poor, while taking care not to create a waterlogged pocket in heavy clay.
Set the shrub at its former growing depth, backfill and firm gently. Water well, then spread an organic mulch over the root area, leaving a gap around the stems.
Growing hydrangeas in pots
Compact hydrangeas make striking patio plants, but they need a generous container with drainage holes. Use good-quality peat-free compost suited to the plant and the result you want. A pot much smaller than the mature root system will dry rapidly and restrict growth.
Choose a stable container that won't tip when the flowers become heavy after rain. In summer, check moisture below the compost surface every day or two, more often in hot weather. A wilted container hydrangea may recover when watered, but repeated severe drying damages buds and flowers.
Move potted hydrangeas to a sheltered spot if late frost threatens their developing buds. Keep the pot raised so rain drains freely; wrapping the pot alone won't reliably prevent the rootball freezing.
How much water do hydrangeas need?
The name is a clue to their thirst, but they still dislike sitting in waterlogged soil. Newly planted shrubs need regular watering while establishing. Mature plants generally cope better, though extended dry weather can quickly affect their broad foliage.
Water slowly around the root area rather than sprinkling the leaves for a few seconds. A layer of garden compost or bark mulch reduces evaporation and competition from weeds.
On a hot afternoon leaves may droop temporarily even when moisture is available. Check the ground before deciding to pour on more water. If the soil is already saturated, investigate drainage and root health.
Does soil change hydrangea flower colour?
For certain H. macrophylla and H. serrata cultivars, soil conditions affect flower colour. Blue flowers generally require sufficiently acidic soil with available aluminium. In more alkaline conditions, the same suitable cultivar may flower pink.
This does not apply to every hydrangea. White-flowered varieties generally don't turn bright blue simply because you add an acidifying product, and panicle hydrangeas follow different colour changes as their flowers age.
If maintaining blue flowers matters, use a suitable variety and an appropriate ericaceous growing medium, then follow specialist guidance. Avoid randomly adding chemicals to garden soil without understanding its pH and the plant's needs.
What should you feed a hydrangea?
In decent garden soil, hydrangeas often need little extra fertiliser. A spring mulch can improve growing conditions while helping the roots retain moisture. A plant in a container may require occasional feeding because nutrients are gradually depleted.
Use fertiliser according to its label. Heavy nitrogen feeding can produce generous leaves but relatively few flowers. If flowering has been disappointing, check light and pruning history before increasing feed.
A newly planted shrub may spend its first season establishing roots instead of covering itself in blooms. That alone does not mean something is wrong.
How to prune mophead and lacecap hydrangeas
Wait until mid-spring to tidy most mopheads and lacecaps. Leave faded flowerheads in place over winter where practical, because they can provide some protection to the buds below.
Cut each old flowerhead back to the first pair of strong healthy buds underneath. Remove dead or weak stems at their base. On a mature, crowded shrub, you can remove a few of the oldest stems to encourage replacement growth without eliminating every flowering shoot.
Don't cut the whole shrub close to the ground annually. That common mistake can produce plenty of fresh leaves and no flowers.
How to prune panicle and smooth hydrangeas
Panicle and smooth hydrangeas generally bloom on new season growth. In late winter or early spring, shorten last year's shoots to suitable healthy buds, following the needs of the particular species and cultivar.
A harder cut can encourage strong new stems with larger flowerheads, but it may also produce growth that needs support. Lighter pruning often results in more, smaller flowers on a bigger shrub.
Always identify the plant first; a pruning method that is right for a panicle hydrangea can spoil a mophead display.
Why isn't your hydrangea flowering?
Late frost damage to the buds is common on older-wood flowering types. Overenthusiastic pruning is another frequent cause. Deep shade, severe drought and an immature plant may also limit the display.
If leaves become brown at their edges, check whether strong sun, wind or irregular watering is stressing the plant. Yellowing foliage might indicate nutrient availability or root problems, so don't assume one symptom has only one explanation.
Look for signs of vine weevil in containers and powdery mildew on foliage. Choose a suitable response only after you identify the cause.
Propagating hydrangeas from cuttings
You can take healthy softwood cuttings in spring or early summer, preferably from stems without flower buds. Remove lower leaves, trim large leaves if necessary and place cuttings into a moist, free-draining propagation medium.
Keep them sheltered and bright, out of strong direct sunshine, while roots develop. Avoid leaving the pot saturated. Once rooted, grow the young plants on in separate pots before placing them outside permanently.
A shrub worth understanding
Give a hydrangea enough room, protect it from prolonged drought and learn which wood carries its flowers. Those three decisions matter far more than complicated feeding routines. A well-sited plant should reward you with colour over many summers.
Source
Royal Horticultural Society: How to grow shrubby hydrangeas.