Hydrangeas are the shrub for shade and for late summer, when most other shrubs have finished flowering: huge mophead or lacecap blooms in blue, pink, white or purple that last for months, on a big, leafy shrub that fills a shady corner like nothing else. They are also one of the few flowering shrubs that genuinely prefer some shade.
The famous trick with hydrangeas is that the flower colour of some types changes with the soil: acid soil gives blue flowers and alkaline soil gives pink ones, and gardeners have been tweaking it with soil amendments for generations. More important than colour, though, is water — the name hydrangea means water vessel, and these shrubs wilt dramatically in dry weather. Give them moisture, shade and a yearly prune, and they flower for decades.
Hydrangeas at a glance
| Growing factor | What hydrangeas need |
|---|---|
| Sun | part shade |
| Soil pH | 5.5–6.5 |
| Days to germination | 14–28 |
| Days to maturity | 365–730 |
| Spacing | 36–60 inches apart |
| Water needs | moderate |
| Cold tolerance | hardy |
| Family | Hydrangeaceae |
Starting seeds
Hydrangeas give you a choice: start seeds indoors for earlier flowers, or sow direct once the soil warms. For the earliest display, sow indoors a few weeks before your last frost — late winter in Zones 3–5, early spring in Zones 6–8, late winter in Zones 9–10 — and transplant out after the frosts end. For direct sowing, wait until the soil is workable and warming: late spring in Zones 3–5, mid-spring in Zones 6–8, early spring in Zones 9–10. Zones 11–13 are frost-free, so both methods work through much of the year; check your local extension service for the best local dates. Seeds germinate in 14–28 days. Keep seed mix or soil evenly moist until seedlings are up, and give indoor seedlings as much light as you can. Our seed starting calculator plans your indoor sowing date, and the germination time calculator estimates when to expect seedlings.
Transplanting and planting out
Transplant seedlings out after the last frost, on a cloudy day or in the evening so they do not wilt in the sun. Space plants 36–60 inches apart — that spacing is what keeps air moving and disease down — and water each plant in well. Our plant spacing calculator works out exactly how many plants fit your bed, and the square foot garden planner helps lay them out.
Soil and feeding
Hydrangeas grow best in fertile, well-drained soil with a pH of 5.5–6.5. Dig in compost before planting — it feeds the soil and helps it hold moisture without getting soggy — and mulch after planting to keep the roots cool and the weeds down. Feed during the growing season with a balanced fertiliser at the label rate, roughly once a month while plants are actively growing, and stop feeding as the season ends. Our fertiliser calculator works out the right amount for your bed, and the compost ratio calculator helps you make good compost to dig in.
Watering
Hydrangeas have moderate water needs: keep the soil evenly moist while plants are establishing and flowering, and water deeply rather than little and often so the roots grow down. Water at the base in the morning so the foliage dries during the day, mulch to hold moisture in, and watch for wilting in hot, dry spells. Our watering calculator gives a starting point for your bed size, and the watering schedule generator can build a routine around it.
Sunlight and temperature
Hydrangeas need part shade — morning sun with shade from hot afternoon sun. Hydrangeas are hardy and tolerate frost and cold weather well, so they can be planted out earlier and left in the ground over winter in most zones. In frost-free Zones 11–13, heat and a lack of winter chill can limit performance, so give them the coolest spot you have. Check your zone with the hardiness zone finder before choosing varieties. Our sunlight calculator can check whether your spot gets enough sun.
Pests and diseases
The pests and diseases to watch for on hydrangeas are aphids, slugs, cutworms. Hydrangeas are generally healthy shrubs. Aphids can cluster on young growth, and slugs may eat low leaves, but the usual problems are water stress and frost damage to buds, not insects. Check plants weekly, looking under leaves as well as on top, and act early. Hand-pick larger pests, knock aphids off with a strong spray of water, and remove badly affected leaves. Keep the area weed-free and avoid wetting the foliage when you water, since damp leaves invite fungal disease. Our pest identifier helper can help identify what you are seeing, and the plant disease checker helps narrow down leaf and stem problems.
Companion plants
Good companions for hydrangeas are lavender, marigolds, garlic, chives. Lavender, marigolds, garlic and chives are good companions, and shade-loving plants underneath help keep the soil cool and moist, which hydrangeas love. Our companion planting finder can suggest more pairings for your bed plan.
Harvesting
Hydrangeas are grown for their flowers, and the harvest is cutting them for the house or drying them. For fresh flowers, cut when the blooms are fully coloured and feel papery rather than soft. For dried flowers, cut in late summer when the blooms have started to dry on the plant, strip the leaves, and hang them upside down in a dry, dark place. Leave the faded flower heads on the plant over winter — they protect the buds underneath from frost — and prune them off in spring. Our harvest date calculator can estimate your picking date from your sowing date, and the vegetable yield estimator helps you work out how much a bed will produce.
Common problems and fixes
| Problem | Likely cause | Fix |
|---|---|---|
| Flowers wilt every afternoon | not enough water | Water deeply, mulch heavily, and plant in part shade. |
| No flowers | pruned at the wrong time, or buds killed by frost | Prune only in spring after the buds show, and leave faded heads over winter. |
| Leaves turn yellow | too much sun, or alkaline soil | Move to part shade and check the soil pH. |
Flowers wilt every afternoon
A hydrangea that wilts every afternoon and recovers overnight is thirsty. Water deeply at the base, mulch the root zone with compost or bark to hold moisture, and make sure the shrub is in part shade rather than hot afternoon sun. A newly planted hydrangea needs watering for its whole first summer.
No flowers
Many hydrangeas flower on wood grown the previous year, so pruning in autumn or winter removes the flower buds. Prune in spring, once you can see which buds are alive, and leave the faded flower heads on over winter — they insulate the buds below them from frost.
Leaves turn yellow
Yellow leaves on a hydrangea usually mean too much sun or soil that is too alkaline for the variety. Hydrangeas prefer part shade and a soil pH of 5.5–6.5, so check your soil and move the plant if it is baking in full sun all day.
Frequently asked questions
How long does it take to grow hydrangeas?
From planting to maturity takes 365–730 days — about 1–2 years (365–730 days from planting). Seed germination takes 14–28 days, and the total time depends on whether you start from seed, a nursery plant, or a bulb or cutting.
How far apart should I plant hydrangeas?
Space hydrangeas 36–60 inches apart. That spacing gives each plant room for air movement, which keeps disease down, and room to reach its full size without crowding its neighbours.
What soil pH do hydrangeas need?
Hydrangeas prefer a soil pH of 5.5–6.5. Test your soil before amending it — most garden soils are close enough, and guessing with lime or sulphur can do more harm than good.
How do I make hydrangea flowers blue?
Blue flowers need acid soil: the soil pH target for hydrangeas is 5.5–6.5, and the bluer end of that range gives bluer flowers. Do not guess with amendments — test your soil first, and know that white-flowered varieties stay white whatever the pH.
When should I prune hydrangeas?
In spring, once the buds start to show, so you can see what is alive. Cut out dead wood and the faded flower heads, and do not prune hard in autumn or winter, or you will remove next year's flowers.