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May 15, 2017 4:57 AM CST
|I'm wondering about temperature sensitive plants. For instance, rhubarb is a northern plant; but I've been successful in growing it in Arkansas. So here's the question: Is it air temperature or soil temperature that is critical? If it's soil temp, a thick layer of mulch should ameliorate the problem.|
May 15, 2017 8:53 AM CST
|This is an interesting question, Rich. As I understand it, for plants that need a certain amount of cold dormancy like rhubarb, it's not so much about either air temperature OR soil temperature but the combination of the two, giving the plant the necessary number of "chilling" hours each winter. Well, I guess the cold air is what cools off the soil, but the soil needs to stay cold for some (I'm not sure how many) hundreds of hours per winter. So a place that is shaded in winter would also help with this as then the sun wouldn't warm up the soil.
So, for growing rhubarb in a (more or less) southern state like Arkansas you are at least getting enough cold weather to chill the plant for long enough that it goes dormant, and re-generates itself each winter to comes back healthy in the spring. If you get a couple of warm winters, you might see the plant declining gradually, though.
You would definitely NOT want to mulch your rhubarb in the winter as that would tend to keep the plant warmer when it needs the cold to stay dormant for it's required sleep. In summer, I'd definitely be mulching it, though, to insulate the root system, keep it moist and generally keep the soil cooler.
For other plants such as stone fruit trees, I think it's prolonged low air temperatures more than soil that they need to keep them from breaking dormancy. But, obviously the one begets the other to a certain extent anyway.
"Success is stumbling from failure to failure with no loss of enthusiasm." –Winston Churchill
May 19, 2017 5:16 PM CST
|At some point, there's no zone-cheating that one can do for a plant, it's either just too cold or not cold enough, over winter. But where the leap is not too great, a mulch is a great way to attempt/augment a microclimate spot. It would moderate the soil temp, and prevent the ground from getting as warm as bare ground on unusually warm winter days, and keep the ground warmer during a cold snap, as well as moderating moisture levels, once it has been in place long enough to have had an effect on the soil below. Whether or not it actually works in a particular spot depends on more variables than just the mulch, but absolutely worth a try, possibly in conjunction with other measures, but not a plant I know to suggest anything specific.
...and I'm assuming the mulch would be an organic one. If not, look for info from someone with experience with a non-organic mulch.
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