How high do temps need to go to 'unthaw' my Nikko?

kuriooo(5)March 4, 2010


I'm in zone 5 MI, and have a Nikko and another semi-hardy to zone 5 hydrangea planted on a south facing exposure.

Last winter was cold and long, and all the flower buds survived the winter, I was so glad as I"ve heard there is mixed success in zone 5 and that most non-flowering Nikkos loose their blooms in late spring through the temps bouncing up and down a lot.

Every day, I"ve been shoveling more snow on top of the hydrangeas to keep them cold as the temps go into the low 40s.

At what point should I worry they are going to become "un-dormant?" Anything I can do to protect the blossoms?


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luis_pr(7b/8a Hurst, TX)

You do that every day? Bless you. I would winter protect them with lots of leaves and remove the protection about 2-3 weeks after your average date of last frost.

If the temps dip below freezing after you remove the winter protection, I would try covering them. If necessary, keep the winter protection longer.

Snow is a very good insulator but I would not do that every day. Sigh. I guess I must be getting old.... Hee hee hee! Oh well.

    Bookmark   March 7, 2010 at 10:42AM
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my concern is the same like kuriooo's: when should I remove winter covers? As long as temps are above zero (0) Degrees Celsius or is it to low? Should temps be at least say : 5 degrees celsius or? I don't know.

    Bookmark   March 7, 2010 at 7:17PM
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Bigleaf hydrangeas may be more susceptible to bud damage from late spring freezes as they are from winter cold. They respond very rapidly to warm late winter conditions and begin to emerge from dormancy only to be cut back by a late frost. I would wait to remove winter protection until you are assured that all chances of abrupt temperature swings and hard freezes are fully past.

    Bookmark   March 8, 2010 at 12:15PM
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So two weeks after mothers day? Mine are the front of the house and such an eye soar. But they are worth it!

    Bookmark   March 8, 2010 at 3:15PM
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Well, I actually have some leaves and burlap covering them, but the stems are poking through the burlap after a long winter of heavy snow on top. I"m actually a little concerned that I'm damaging the buds now, because of the snow. But temps are going to be in the 50s this week, and it is definitely going to get cold again here in Southeast MI.

My last frost date is mid-May, so I"ve got a while to go.

Is it the lack of light that keeps them dormant inside of a winter protection or staying cold? Or both?


    Bookmark   March 8, 2010 at 11:04PM
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Just so I make myself clear......:-) Spring frosts are not a concern. Even macs out of dormancy can tolerate light frosts with ease and with no damage to flower buds - mine, which get NO protection, experience this all the time. What you DO need to be concerned about are abrupt changes in temperatures that can result in hard freezes, like the big Easter freeze of a couple of years ago that decimated all manner of perfectly hardy plants just beginning to push new growth.

I do not see problems with removing winter protection as soon as your climate shows the typical signs of spring. Just be prepared to do some emergency protection should the weather forecast predict unusual lows.

btw, dormancy is both a factor of light (day length) and temperature :-)

    Bookmark   March 9, 2010 at 10:30AM
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whoa...two weeks after last frost would darn near bring me to June 1. Wait that long and you will likely have etiolated growth under the cover. When it has been sufficiently warm long enough, the plant will start growing in the dark.

I start pulling back the mulch as it thaws in April. In my area, by the end of April a hard freeze is bordering on record low temps so, as in the previous post, staying aware of the forcast is a must.

    Bookmark   March 10, 2010 at 7:12AM
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