I overwinter plants hardy to zone 6 (same zone I am in) in pots, using chopped-up leaves as mulch. Pots are sitting directly on ground, I only put a layer no more than 1-2" on top of soil, but more around the pot itself. Also surrounded by a 'cage' made of chicken wire to make sure the leaves don't get blown away. Grouping pots also helps, leaving some space between pots filled with leaves too. Most important, I think, is to make sure there is good drainage. If water sits in the container, the roots may rot. I don't think more than that would be needed unless you try to overwinter plant rated for lower zone than yours - like the fig tree: friend of mine built a wire cage around his fig slightly taller than tree (after pruning so it's not so wide); wrapping this cage with burlap and filling it completely with leaves (straw is good too), covering top of the tree with few inches of it too. I read (maybe here on GW?) that you could build enclosure and have christmas lights inside (not led) and they would warm-up inside sufficiently...and here is a link to thread using fluorescent lights in styrofoam enclosure: http://forums.gardenweb.com/forums/load/farnorth/msg1211132530111.html Rina

Good points: Helps prevent roots from freezing by insulating. For most deciduous trees that is not a problem. For evergreens that survive freezing not a problem because their canopy protects their roots down below. For trees that are not cold hardy, die back and can grow out again from rootstock I'd say a thick layer of organic mulch (wood chips) is indispensable. As was said, organic mulch breaks down adding a slow release fertilizer effect to the tree. But this process is slowed down in the winter. Bad points: We get 3" of rain on average in the Dec-Jan period. A layer thicker than 4" can block water from absorbing onto the ground immediately below. I don't really consider this a problem. If you are using frost cloth part of the trick is to let the ground heat up in the daytime. It may be best to pull the mulch back from the dark ground in winter and let this solar process happen. [can inspect underling drip irrigators too as spring approaches] But a decomposing mulch pile generates some heat that would help in the evenings under a frost cloth, so. . . . Pulling mulch away prevents rodents overwintering in it next to the tree. I have not had a problem with this but it is common problem in other states. For the most part, I'd leave it in place. keeps the ground from getting to cold and maintains soil moisture.

I'm going to have tonnes of woodchip soon as I'm getting rid of several large African Mahoganys. I use a lot of leaves and woodchips to protect the soil during the rainy season. It more than compensates for the small amount of nitrogen draw down. The trees provided a lot of the leaves I used but their chips will last longer. In any case, I've still plenty more Mahoganys (and other trees) to keep up a good supply of leaves. And the new piles of wood chip should keep me going a number of years as well. It's important to keep that organic cycle going. (BTW Funnelweb, I finally got GW to change me back into an Australian male. Guess if you whinge enough .... "It's the squeeky wheel that gets the oil". My first squeek was back in January.)

is this even a thing in z7? in my ground freeze MI ... we want the ground to freeze.. and stay frozen all winter .. in snow cover thats pretty easy ... the snow itself keeps winter sun off the dark soil.. so no thawing of the dark soil from winter sun ... also ... if no snow.. winter winds can pull a lot of moisture out of exposed soil ... and on babe trees .. with not so deep roots ... it could be a problem... since you cant really winter water frozen ground for fear of making an in ground ice cube.. and roots need air as much as moisture .... [not to mention frozen roots that dont really pump water.. and desiccation of evergreen leaves and trunk issues.. in colder zones...] if your ground does not freeze.. and you could basically water all winter long if need be in some extreme winter drought.. then why waste the mulch ... if you need it elsewhere ... one of the problems with the WWW .. imo ... is sourcing of website knowledge ... how do you figure out if the source even applies to your location ... ken