Cold Weather Gardening Tip: Ah, so that's why!

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Cold Weather Gardening Tip

By SongofJoy
November 9, 2012

Watering before a predicted freeze helps outoor plants, especially container plants, make it through a hard freeze by allowing the plants to take up moisture before the soil or ground is frozen, preventing water from reaching the root zone. Making sure your outdoor plants have adequate hydration is one of the best ways to protect them from harsh weather.

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Name: Renée
Northern KY
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KyWoods
Nov 8, 2012 8:10 PM CST
I remember hearing that you should water before a freeze, but I couldn't remember why. Hilarious! Thanks!
Name: Carole
Clarksville, TN (Zone 6b)
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SongofJoy
Nov 9, 2012 4:41 AM CST
I tip my hat to you. It's difficult for me to want to water in the cold sometimes even when I know I should. *Blush*
The best and most beautiful things in the world cannot be seen or even touched -- they must be felt with the heart. ~ Helen Keller
Name: Rick R.
near Minneapolis, MN zone 4a
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Leftwood
Nov 9, 2012 11:09 AM CST
It's hard to know if the author is talking about temporary freezing or long term, so I don't know if what I have to say is relevant. If watering is for the long term (winter), then I have some important points:

--- One wouldn't want to water a container just before a freeze. (I am assuming we are talking about winter dormant plants.) Plant hydration in cold weather takes a whole lot longer than in the summer or at room temperature. Not only is this because of the temperature itself, but most plants that go dormant in winter also slow their inherent ability to take up water. Watering the evening prior to a freeze would more likely detrimental than advantageous. Water uptake by the plant would be negligible in, say, six hours, and excess water in the soil wouldn't have time to drain thoroughly. If the soil in the container freezes, this frozen excess water is likely to damage roots as it quickly expands, not to mention cracking the container if it is vulnerable.

Better to water containers a couple days before a predicted freeze. Remember, if it is cold out, plants don't use much water, either. If we are talking about plants in the ground, then it doesn't matter. The ground won't freeze abruptly so as to cause such problems.

--- For marginally cold hardy herbaceous materials, the advice to water does not apply. Marginally cold hardy plants are marginal because they have difficulty attaining sufficient cold hardiness. Usually, it is because these plants don't begin the transition from summer growth to winter hardening early enough, and/or don't attain enough freeze resistance in time for the cold weather. Watering can help prolong the summer phase and delay the transition. Withholding water, or at least withholding extra water usually helps begin the hardening phase.

In addition, slightly withered root structures tend to survive colder temperatures better than fully turgid ones. (Remember, an herbaceous plant has no leaves to support.) Less water within the plant itself means soluble compounds are more concentrated in the plant's sap. The more concentrated an aqueous solution, the lower the freezing point. Thus, the plant has more cold hardiness. In fact, this is a major mechanism used by nearly all plants to resist freezing. Naturally moving water out of vulnerable plant tissues leaves a higher ratio of non-water compounds to water. This results in a solution that resists freezing better.

A good analogy is salting your ice covered driveway. You are creating a water and salt solution that has a lower freezing point,(= lower melting point). So the ice now melts at the same temperature where it was frozen before (and without the salt). But if the ice still doesn't melt, you put on more salt. This makes the solution more concentrated with salt (= a higher ratio of non-water compounds[salt] to water). The melting/freezing point lowers even more, and the ice melts.

--- The big push for watering winter dormant plants in the fall is for evergreens. For herbaceous and deciduous woody plants and barring a fall drought, watering more than normal shouldn't be necessary unless you're planting or transplanting.
Name: Carole
Clarksville, TN (Zone 6b)
Cherish today
Charter ATP Member Garden Sages Plant Identifier I was one of the first 300 contributors to the plant database! I helped plan and beta test the plant database. I helped beta test the Garden Planting Calendar
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SongofJoy
Nov 9, 2012 11:26 AM CST
Thanks for adding all those points, Rick. Not talking about marginally cold-hardy herbaceous plants, mostly container specimens. I thought some of it would be obvious but maybe not. And as stated, "before the soil is frozen". Anyway, glad you added some info for clarity in case there are questions.
The best and most beautiful things in the world cannot be seen or even touched -- they must be felt with the heart. ~ Helen Keller
[Last edited by SongofJoy - Nov 9, 2012 1:02 PM (+)]
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