The methodology used to arrive at the Canadian Zone Numbers differs from the USDA’s approach and so one zone 4 location may not be equal to the other zone 4. They both use different averaged annual minimum temperature ranges -not actuals- so your real life actual temperatures can be colder than these averages.

For example, on Jan 1st, Calgary hit a low of -36.2C. That is lower than the minimum zone 4 temperature definition of both USDA and AAFC/Agriculture and Agri-Food Canada.

Based on your results, I would not try another z4 macro unless the rating is clearly given as Canadian Zone 4 and unless you think you may have had sub-zone 4 temperatures for a short time this last winter that will not re-occur again. ;o))

In what town do you live now? I seem to think you were in Calgary, no? Maybe you can grow it in a pot and move it somewhere warm during winter instead of planting outside. Most new releases of remontant macros now a days tend to be compact, around 3 feet, meaning they are not huge like the 5-6 footers that we used to buy decades ago and which where to difficult to move/store indoors due to their big dimensions.

Thanks, luis and rouge!

Luis, I was in Calgary before but now I am in Edmonton! It is further north but actually for the purpose of gardening, plants and trees do better here due to the more consistent temperature during winter here than in Calgary! Calgary is wild with the chinooks - good for humans but not so good for the plants!!! LOL!

I was just really missing the gorgeous Endless Summer hedge that I had when I was in Ohio (zone 5). Yes, even that was pushing it a bit but then they were in a protected location so they did very well! But I have given up trying now - the Pop Star just did it in for me! LOL!!! I think that FB has been successful in growing some macrophyllas in the ground but I just have not had such luck! Sigh!

I have seven Pop Star hydrangeas. They are all in containers. Five were in my shed for winter. The two that were in containers that were too large to move survived winter much to my surprise. They were against the house in a more protective location and I did cover them with tons of leaves so that must have helped.

chrysalids, one of these days, I will try container planting again! I tried that before, but it did not work out well so I just gave up.... so what zone are you in please? How early do you get blooms for Pop Star? Also, how soon do you take them out of your shed, and do you acclimatize them gradually as you take them out of your shed during spring please? Thanks!

@ ostrich, I am in zone 6a in the northeast. I took the hydrangeas in containers out of my shed mid-April when I was sure that there would be no more cold snaps. I never acclimatize them gradually. We had a warm spring so I took them out earlier than usual. The buds had begun to open up in early April which made me worried about them staying in the shed for much longer. All the hydrangeas including the Pop Star had full blooms by mid-June. Again, this is due to the unusually warm spring that we had in the northeast.

chrysalids, I so wished that I were in Zone 6!!! SIGH!

It is amazing that you didn't have to acclimatize these babies! I tried to do potted tender roses before but they did not do well for me.... I guess roses must be fussier???

I was recently in USDA zone 3b until the upgrade of 2023 made me 4a. Yippee! ;-)

I was gifted this H. macrophylla 'Bloom struck' a couple of years ago. Planted from pot in May of 2022.

Took right off and by June 16, 2022, it really looked okay.

It's first winter in the ground, we had oodles of deep snow all winter and cold, and the plant came through that one with zero winter kill. The big trouble here is that after the snow melted, we had freezing temperatures that took out some of the branches and flower buds present from the season before.

6-30-2023:

After some pruning of dead stems, there were still some early flowers from the previous season's buds. Nothing spectacular but for first winter in the ground, I got something even though the blooms were pinkish white in color.

8-29-2023:

After the early flowers died and were deadheaded, more buds came from new wood and even though a little on the pink side, it was a pleasant display.

Last winter we only had snow for short periods of time and not any terribly low temps.

The plant was covered with a 2ft. high cylinder of dead leaves, but it basically still froze to the ground except for a few stems in the 1" long category.

So, no early flowers from last season's buds.

The plant pushed new stems and soon flower buds.

This is what it looks like this morning. 7-19-2024:

Blue again and all blooms coming from new wood and new buds.

My biggest trouble is, it's getting full sun, all day which has scorched some of the flowers and has to be watered every day to prevent sun damage.

Other than that, I plan of just a covering of wood mulch over the root zone this winter. The leaves I used stayed wet and went mushy during warmer spells during winter so didn't offer much winter protection really and the only obvious return will be from several inches of wood much protecting the roots, so we'll have another comeback from the ground next spring.

:-)

Excellent post "Bill. I love the detail.

5-4-2025:

I moved that blue hydrangea, pictured above, from the front yard a few days ago. It was suffering badly in that location and was powerless providing shade without building some sort of structure. So, if you can't move the shade to the plant, you have to move the plant to the shade.

I'll see if it does anything later this season and report on that.

Wish i could grow the macrophilias. I have a limelight and an annabelle that survived for me

Mine didn't like the transplant but new shoots are coming from the ground already.

It needs water frequently to thrive.

Noticed a little cauliflower forming.

The shade begins around 3pm and gets a little dappled/ambient sun until sundown. So much better this way.

I'm in Zone 5b, NW Illinois and my "Pop Star" did come back. We had a mild winter and I also covered it really well with a ton of mulch. Mine has a few buds.

7-18-2025:

Looks pretty good considering it was just transplanted this spring after a fairly cold winter.

Thought I'd better get a picture now; just in case something happens.

If it does get a lot better later this season, we'll see but to me, it's a success and it should get better as the root mass increases for next year.

The color was a 'Viking Purple' but looks bluer on the picture. :-)

5-2-2025:

Transplanting it was the things nightmares are made of. j/k

Must've been over 200 lb. (wet) root ball. ;-)

Below is the destination hole, just before re-planting (root ball is on a tarp that's covering my little blue snow sled).

8-10-2025:

Not bad for a new location this season. ;-)

10-9-2025:

Put to bed for the winter, with an extra thick covering of wood mulch.

I've tried keeping the old wood and buds until spring but that doesn't work this far north. So, protecting the roots over winter at least gives me new growth that produces new buds and flowers next season. ;-)

It enjoyed the mixed sun and shade in its new location.

Didn't have leaves drooping like it did in direct, all-day sun.

It needed watering in late season due to lack of rain.

Hydrangea Macrophylla 'Bloom Struck'.

8-18-2026:

All good things must come to an end.

After a not too bad winter with a snow cover of ~2ft. deep the whole time, an early warm up in the middle of April, followed by well below freezing temperatures the next week, must have affected the above plant. It came back very weak and with plenty of water and some fertilizer, it appeared promising for making a comeback.

Then the weeks of upper 90's to low 100's dragged on, accompanied by a terrible dry spell.

I watered twice a day, every day but even in the new shady area, the plant continued to decline, to the point that it was me that was getting exhausted, trying to save it. So with my summer dry spells and coarse sandy soil, I removed it just because it would be too much work to keep it happy.

I need more drought resistant plants here, to even have a facsimile of a garden that's not too water intensive (note color of grass from a month of dry, hot weather/dry 2ft. deep). i.e. The cotoneaster on the right flourished and grew 18", with just occasional watering.

It was fun while it lasted. :-)