How to Prune Endless Summer Hydrangea
Why the best cut is usually a small one, and where in Canada this hydrangea is a gamble.
How to prune Endless Summer hydrangea in Canada is mostly a lesson in restraint. It is a bigleaf hydrangea (Hydrangea macrophylla) bred to flower on both last year’s wood and this year’s, and the University of Massachusetts points out that even on these reblooming cultivars most of the flowers still come from the old wood.
So every stem cut in fall, and every live stem cut in spring, is a stem of early flowers you will not see. The University of Minnesota’s comfort is real, though: because the Endless Summer series flowers on new wood too, it blooms whether you prune it or not.
Endless Summer pruning at a glance: Do not prune in fall. In spring, wait until new growth shows, then cut dead stem tips back to the first pair of live buds and take fully dead stems out at the base. Remove a few of the oldest stems on a mature plant. Deadhead in summer. In Zone 4 and colder, expect leaves more often than flowers.
Why Spring, and Why Late in Spring
The University of Massachusetts says pruning should be done in spring as new growth resumes, when living branches can be told from dead ones. The University of New Hampshire gives the same advice for bigleaf hydrangeas: wait until new growth appears. Cut too early in spring and you are guessing which stems survived.
In most of Canada the leaves show late, often well after your last frost date. A stem that looks dead in April may leaf out in May, so give it time before you write it off.
Step by Step in Spring
- Wait for the first leaves. Swelling green buds along a stem mean it is alive to that point.
- Find the line between dead and live. The University of New Hampshire’s test: a live stem is green inside when you scratch it, a dead one is brown.
- Cut dead tips back to about 6 mm (a quarter inch) above the first set of live buds.
- Take fully dead stems out at the base.
- On a mature plant, remove a few of the oldest stems at ground level. The University of Massachusetts suggests taking out stems three years and older to keep the plant’s structure.
Spring on an Endless Summer is mostly small cuts back to the first live buds; the lopper is for the odd old stem you take out at the base.
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Deadheading in Summer
The University of Massachusetts suggests removing old bigleaf flowers when they turn brown, cutting just above the next set of leaves. If the plant has grown too tall, it says, shorten it right after the flowers fade, and better still, plant it where it can reach its natural size. The University of Illinois puts the cut-off for old-wood bloomers at August 1, because next year’s buds start forming in August and September.
Where Endless Summer Is Risky in Canada
The University of Massachusetts rates bigleaf hydrangea for a mild US zone, says it needs protection one zone colder, and notes that even the cultivars sold as hardier commonly suffer winter damage. Those are US zones, so they rank the plant rather than placing it in a Canadian garden. Here is how this site reads Canadian cities for an old-wood hydrangea like this one:
| City | Canadian zone | Our read |
|---|---|---|
| Victoria | 8b | Flowers reliably most years |
| Vancouver | 8b | Flowers reliably most years |
| Kelowna | 6b | Usually flowers; protection helps in a hard winter |
| Calgary | 3b | Risky: often leafs out without flowers |
| Edmonton | 4a | Risky: often leafs out without flowers |
| Saskatoon | 3a | Risky: often leafs out without flowers |
| Winnipeg | 3a | Risky: often leafs out without flowers |
| Toronto | 6b | Usually flowers; protection helps in a hard winter |
| Ottawa | 5a | Sheltered spot and winter protection; expect off years |
| Montréal | 5b | Sheltered spot and winter protection; expect off years |
| Québec City | 5a | Sheltered spot and winter protection; expect off years |
| Fredericton | 5a | Sheltered spot and winter protection; expect off years |
| Charlottetown | 5b | Sheltered spot and winter protection; expect off years |
| Halifax | 6a | Usually flowers; protection helps in a hard winter |
| St. John’s | 5b | Sheltered spot and winter protection; expect off years |
Zones are this site’s city data (Natural Resources Canada). The right-hand column is our own guidance for plants that carry their flower buds through winter, not a published rating: extension hardiness ratings for hydrangeas use US zones, which are built differently from Canadian ones.
The new-wood flowers are the safety net in the colder rows: after a hard winter the plant can still flower later in the summer, just less. If you want reliable flowers every year in Zone 4 or colder, a panicle hydrangea such as Limelight is the better bet.
Winter Protection and Colour
In Zone 5 and colder, protection is what keeps the old-wood flowers. The University of Minnesota also recommends a ring of hardware cloth about 1.2 m (4 feet) tall around bigleaf stems, because rabbits browsing the stems remove the buds as surely as cold does. The full method, from the leaf-filled cage to uncovering in spring, is in Hydrangea Winter Care in Canada.
Endless Summer turns blue or pink with the soil. The University of Massachusetts gives a soil pH of 5.5 or below for blue and 6.5 or above for pink; Hydrangea Colour and Soil pH explains how to move it. Pruning does not change the colour. For every other hydrangea in the garden, keep the printable pruning chart handy.
Frequently Asked Questions
When should I prune Endless Summer hydrangea in Canada?
In spring, once new growth appears and you can see which stems are alive. Cut dead tips back to the first live buds and remove fully dead stems at the base. Do not prune in fall.
Can I cut Endless Summer hydrangea back in the fall?
It is better not to. Most of its flowers still come from buds formed the summer before on old wood, so a fall cut removes them. The plant will still flower on new wood, just later and less.
Will Endless Summer bloom if I prune it?
Yes. The University of Minnesota notes the Endless Summer series flowers on both last year's wood and new wood, so it blooms whether you prune it or not.
Is Endless Summer hydrangea hardy in Canada?
The roots usually are; the flower buds are the problem. In Zone 6 and warmer it usually flowers well, in Zone 5 it needs a sheltered spot and winter protection, and in Zone 4 and colder it often leafs out with few or no flowers.
Why is my Endless Summer hydrangea not blooming?
Usually a hard winter killed the old-wood buds, or the plant was cut back in fall or early spring. Too much shade, too much nitrogen and drought can also cut flowering.
Should I deadhead Endless Summer hydrangea?
You can. The University of Massachusetts suggests cutting old bigleaf flowers off just above the next set of leaves once they turn brown. Finish any shaping cuts by August.
Sources
- University of Minnesota Extension — Pruning hydrangeas for best bloom
- University of Massachusetts Amherst Extension — Why Hydrangea macrophylla Don’t Flower
- University of Massachusetts Amherst Extension — Growing Hydrangeas
- University of New Hampshire Extension — Pruning Hydrangeas
- University of Illinois Extension — For showy blooms, pruning hydrangeas is all about the timing
- Canadian zones and frost dates: this site’s city data, from Natural Resources Canada and Environment and Climate Change Canada.