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pondering Dormancy

Posted by landperson 8b CA (My Page) on
Sat, Sep 17, 11 at 10:46

Last night I found myself wondering about the relationship (is it linear?) between dormancy and death in a rose. I think when some plants (maybe Hostas) are water stressed they simply retire early into dormancy and then return in the next season (with water of course). I also remember in nursing school being taught that surgical anesthesia puts us into a state that is as near death as possible (from which we can hopefully be brought back). And, so that all makes me wonder whether dormancy is just a pre-expiration for the plant until the necessary requirements for its life are restored (heat in particular) and ....

okay, finally the practical part of my question: IF at the very end of the season a rose were not watered would it simply go into dormancy early and be likely to return in the spring, or would it simply die.

Just curious.

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RE: pondering Dormancy

  • Posted by seil z6 MI (My Page) on
    Sat, Sep 17, 11 at 11:40

Die. That's why it's recommended that you water them very well just before they go dormant for the winter and before you place any winter protection on them.

RE: pondering Dormancy

I think it depends 100% on the climate, and what kind of rose it is. Roses go dormant when it is very cold, very hot, etc. I am told they can survive here in our climate w/o extra water during our 5-6 month hot summer drought, but of course they would not bloom or grow then, just survive.

Seil's answer is correct for the zone 6 in MI, as the roses need to be hydrated going into the winter freeze. In my zone 9 in CA, if I stopped watering "at the end of the season", it would not matter, as the 4-5 months of winter rains (we get about 40 inches- all during the Winter) would still come soon, and the roses would be fine. Does it freeze hard in the Winter where you live in zone 8b in CA? If not, then the answer would be the same as it is here.

I think most questions about roses always depend on the type of rose, and the exact kind of climate.


RE: pondering Dormancy

Thanks, Jackie and Seil.
I am probably only about 30-40 miles north of you, Jackie, so I'm guessing our growing parameters are quite similar. I had a pipe-freezing freeze back in the mid-80's once, but otherwise we get light freezes and "winter protection" is a non issue.

I'm still curious about the science of the difference between dormancy and death and whether they were/are a continuum.

RE: pondering Dormancy

Good morning! This is another of those wonderful questions which is best answered with "it depends".

European OGRs "evolved" in harsh, cold climates (in comparison) and extreme cold and lower light levels for long periods force them into dormancy. These tend to be the ones which require the chill hours to perform well, and the ones which aren't really good in climates not providing those chill hours. Growing them in those areas is like growing high chill stone fruit in warm climates. They may grow, but you'll have little flowering and fruit.

Evergreen roses from China, etc., evolved in a climate without that type of cold, for the most part, and go "dormant" with lack of water. Modern roses, being the mixed bag of confused signals they are, go dormant mainly from lack of water. Xerophytic species such as Minutifolia, Stellata, Persica, will actually go into a suspended animation with lack of water and high heat levels, but explode quickly back into growth with water, preferably winter rains. Some are like native California Oaks, lacking the symbiotic fungi necessary to process summer water unless they germinated in soil with summer irrigation.

Most roses (and other plants) will go deciduous (even evergreen ones) with high water stress to reduce their need for water. They'll remain there until they either sun scald enough to be killed; use up their reserves to the point of death; or are irrigated in time to resume their normal functions.

Roses in more severe cold require water so their cells are full, preventing formation of ice crystals in the cells which pierce the cell walls and cause the "freeze damage" many experience.

It was a real eye opener for me to work the harvest in Wasco one year. Even with day temperatures in the twenties, many roses were fully leafed out and flowering. They had to be sprayed with a heavy horticultural oil to burn off the foliage and force them into dormancy for harvest. Though there was "cold", they had enough sun, rain and ground water to remain productive, requiring them to be forced to stop growing and flowering. Very interesting. Kim

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