Hydrangea Year: What to Do Each Season, and When

Late winter to early spring: the only window for hard pruning

While the shrub is still dormant, but with the buds beginning to swell, is when new-wood types are cut back to their framework. This is also the moment to remove dead wood from any hydrangea, since dead stems are obvious against the bare framework and there is no penalty for cutting them at any time.

Do not touch the old-wood types now beyond dead wood. Their flower buds have been sitting on the stems since last summer, and every stem you shorten is a flower head removed. If you left the spent heads on over winter for frost protection, take them off now, cutting only back to the first pair of fat buds.

This is also when to check and top up mulch, and to clear away fallen leaves from the base where fungal spores overwinter.

Spring: bud break, frost and the first feed

Once the buds break, the shrub is committed and vulnerable. A frost of a few degrees below freezing after the leaves have emerged blackens the new growth and, on old-wood types, takes the flower buds with it. The plant recovers and looks fine by midsummer, but produces no flowers that year. If a late frost is forecast after bud break, throw row cover or an old sheet over the shrub for the night and take it off in the morning.

Feed as the buds break, not before. A balanced granular fertilizer spread over the root zone and watered in is all that is needed. Follow it with two to three inches (5 to 8 cm) of mulch, kept an inch clear of the stems, which will save you most of the summer watering.

Late spring is the propagation window. The shoots are flexible but no longer floppy, which is exactly the stage softwood cuttings want, and it is the best moment to pin a low branch down for layering.

Newly planted shrubs need water twice a week through their first full growing season regardless of rainfall. Their roots are still confined to the original rootball and cannot reach the surrounding soil moisture.

Summer: water, support and do not prune

Summer is maintenance rather than intervention. The one skill worth practicing is the morning wilt check: leaves flat at dawn mean genuinely dry soil and need a long, slow soak, while afternoon drooping that recovers overnight is normal and needs shade, not water.

Big flower heads catch rain and get heavy. A head full of water on a long stem will bend it to the ground and often crease the stem permanently. Stake or ring-support the heaviest stems before the flowers reach full size rather than after the first storm has flattened them.

Resist tidying. Any cutting done to an old-wood type during summer beyond removing spent heads takes off wood that is about to set next year's buds. If the shrub is genuinely too big, note it and deal with it properly straight after flowering.

1. Check at dawn, not at noon Look at the shrub first thing. Limp leaves in the cool of early morning are the only reliable sign that the soil is dry. Water then, deeply, and leave it until the surface dries again.
2. Soak, do not sprinkle Wet the top eight to ten inches (20 to 25 cm) of soil when you water. Frequent shallow watering pulls roots to the surface and makes the plant less able to cope with the next hot spell.
3. Support before the heads open fully Put a ring stake or a few canes and twine in place while the heads are still small. Trying to lift a flattened stem after rain usually breaks it.
4. Keep the air moving Thin any crossing stems in the middle of a congested shrub. Still, humid air inside a dense plant is where powdery mildew starts, usually on the lower shaded leaves first.

Late summer and autumn: the second decision point

As soon as the main flush of flowers has gone over on an old-wood type, prune it. This is the narrow window: bud set for next year begins within a few weeks of flowering finishing, so a prune done now removes only spent wood, while the same cut a month later removes next year's flowers. Deadhead to the first strong pair of buds and thin up to a third of the oldest stems at the base.

Feed once more at this point with something low in nitrogen and higher in potassium, supporting the bud set rather than pushing new leaves. Then stop feeding entirely about eight weeks before your first expected frost, so the season's growth has time to harden.

Autumn is the best planting season. Soil is still warm, rainfall is reliable, and the roots establish before winter without the shrub having to support a canopy of leaves. It is also the time to make soil pH adjustments, since both liming and acidifying take months to move through the soil and show in the flowers.

Winter, and the notes that make next year easier

In cold gardens, leave the dried flower heads on old-wood types through winter. They shelter the buds immediately below from frost and drying wind, and a shrub in an exposed position is worth wrapping loosely in row cover or surrounding with a collar of straw over the crown. Container plants are far more vulnerable than those in the ground because the rootball freezes solid; move pots to a sheltered wall or an unheated shed.

Winter is when the record pays off. Look back at the dates you wrote down: when the first color showed, when the last flower faded, when you pruned and how hard, when your last spring frost fell, and how each shrub performed. Those five lines explain almost every hydrangea disappointment, and they let you set next season's pruning date before the buds start moving rather than after.

Note the position of each shrub and the hours of direct sun it actually gets, checked in midsummer. Shade creeps up over years as trees and hedges grow, and a written baseline is the only way to notice it happening.