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Is a plant, whether in the ground or in a pot outside, more resistant to frost damage when it's soil is drier or freshly watered?

context: mid-Spring right as hardwood trees are budding. I'm mainly interested in potted young deciduous trees but would also appreciate learning what's best for other kinds of plants. It's raining a lot around this time so I figure the trees on the ground can handle a night of near freezing temps after being freshly watered. What's best for the potted trees though, to be watered or not to be watered (and dry from having minimal watering) right before a 0dC night?

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If you're asking whether the soil in your potted trees is better being damp when you know cold weather is coming, yes, it is, so watering if necessary, preferably in the morning to give the plants time to take up the water, is a good idea. Frost damage can still occur on newly opened, young leaves, but frost and freezing are not always the same thing - there are 3 or 4 different types of frost, notably air frost, ground frost, grass frost, hoar frost, all with varying degrees of freeze. Grass frost is the type where man made surfaces show no sign of frost, but the grass and plants do. As your plants are in pots, make sure you don't leave them in a place that gets early morning sun, to give the frost time to dissipate before the sun hits the leaves, and that will spare them from some damage too. More guidance on watering here, though it's primarily more about possible freezing than frost, but may still be of interest https://www.todayshomeowner.com/when-to-water-plants-before-a-freeze/

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  • Just above 0dC is expected in my area tomorrow night so I'm watering today. Potted trees are in an enclosed porch now, and night before the frost I may hang up covers on the porch windows to dim/block the eastern light and add some insulation. If it was colder I may also wrap the plants in some row cloth as @stormy suggested or towels around their pots, or if it was real cold I'd bring'em into the basement for the night. Potted plants may be more challenging but also offer more flexibility while they get through smaller growth stages!
    – cr0
    May 7, 2017 at 0:32
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    If they're in an enclosed porch, specially if it has a roof, with temps as you describe, the frost won't get at them, and that sort of temperature is insufficient to freeze the soil in the pots, so not too much of a problem really.
    – Bamboo
    May 7, 2017 at 1:25
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Watered believe it or not. The best solution is to WATER with an oscillating sprinkler BEFORE morning. Watering like this actually slows the already frozen cells in thawing. Fast thaw is what kills most plants or plant material subjected to a freeze or frost. Watering slows the thawing down. Healthy plants will be able to recover. So yes, water them. Get up in the dark mornings to check your garden for freezing. If there was a freeze and you've got frozen plant material start watering. Seriously, this slows the thaw process down so that there are less plant cells bursting when those cells go from frozen to thawing.potato plants after a night of freezing. I barely got out there to water but only the tops froze. Plenty of foliage to continue to make potatoes. I just lopped the ruined foliage off.

BUT WAIT! You've got to get some 'row cloth' to wrap your babies in BEFORE night time and the chance of freezing. This stuff, white, permeable to water and light...is a gardener's best friend. Also stops insects during the time they want to lay eggs on or near your plants. Just dump soil all around the edges so the flies or moths are unable to crawl beneath.

This row cloth is purported to maintain temps that are 10 to 20 degrees higher than the outside temperatures. Plants in pots are very susceptible to cold and freezes...the weakest part of plants are first; the deciduous leaves which usually abscise to fall and depart the plant to protect the plant. The next are the roots. In a pot, plant roots are terribly unprotected from cold. If the frost or freeze is no big deal plant roots should do fine. For very sensitive plants or plants planted in pots left out side in an exotic zone (tropical plants trying to endure non tropical zones and temperatures) I have used heated wraps, Christmas lights and lots of burlap to allow those plants to survive a few too cold nights...wind. Row cloth on the potatoes in my picture would have not allowed those leaves to freeze. I forgot to deal with freezing that night. Bummer but not a deal breaker. ROW CLOTH. Gotta have it to extend your seasons and protect from sporadic freezes!

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  • Good point about slowing the thaw! I was asking about watering as prep before the frost. Is it better plants go into the frost dry or wet? It sounds like go in dry so they can be watered after the frosty temps are receding?
    – cr0
    May 6, 2017 at 23:27
  • Just added more info for a far better answer. Plants needing water will not do well as they are already stressed. ROW CLOTH. Have you heard of it?
    – stormy
    May 6, 2017 at 23:32

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