This topic has come up often. You may be able to find old threads on "overwintering".

The one agreed-upon requirement for midwestern growers is to send the plants into the winter with good moisture in the pots. If they freeze wet, they'll be fine. If they freeze dry, you may have significant winter loss.

Beyond that, there are apparently lots and lots of ways to overwinter stock successfully, limited only by means, materials at hand, and imagination. I block out the pots, and cover with fabric and/or mulch. I suggest you talk to local growers to see what works well in your area.

I would personally be hesitant to pot plug/bare root in the fall, simply because that is a limited root system, and may have problems with winter dessication. Unless you have absolutely no facilities at all, why not pot in late winter, grow on in hoop houses, and have the stock ready for spring sales?

Good luck with your project. This business can be very rewarding. Sometimes, too, it is a royal pain in the butt!

Brian

Can't say how well it will work in your climate but here in zone 7/8 I overwinter a lot of perennials outside under horticultural fleece without too many losses.

Sometimes I have had better success than under tunnels as there is less dehydration and smaller night/day temperature differences.

In terms of plant hardiness in containers, generally evergreens are the least hardy, then the woodies and the true perennials that die back are the toughest. If in doubt, choose stuff that is at least one hardiness zone less than yours.

Good luck

Vouts

I am in z6 - so this info should overlap somewhat. Although here in z6 - There is a good fall planting season -and in z4 I avoid doing alot of fall planting - so I don't know where you fall? Anyway at one local perennial nursery where I worked - we wintered perennials over in one of three ways - A> we moved the 1 - 2 gallon plants pot to pot outside and covered with evergreen boughs (unsold x-mas trees) in late december. These were usually older plants and tough common varieties. B> We kept one hoophouse unheated and filled it pot to pot with 1-2 gallons and trays of 4" pots. These were younger plants, newer varieties where hardiness was in question and also things that bloomed really early (so we didn't miss the bloom under the bough covering). This house had fans going when the temps rose and was watered occaisionally. C> Lastly there were some things put into a heated hoophouse. These were plants that my boss felt were tender and also anything she wanted me to propogate during the winter. Again these were 1-2 gallons and 4" pots. There was another heated house for all the bareroot and liners and seedlings that were potted up in the late winter early spring - though some of that stuff went went directly outside too.
Hope this helps!

Whatever you do don't use straw. We used it last year and had a mole infestation in spring. Took months to get them and they ate hundreds of roots. Althought the straw helped overwinter some plants it was too much protection for others such as mugo pine. We have a small nursery with a greenhouse and sell about 5000 plants per year. My advise at this size would be to try and get rid of as many plants as possible. In the spring we import bare root plants and plugs and dig up propogation beds (which don't need any protection! if you grow perennials as we do) This year whatever we have left, it may be a few hundred. We will stick in the unheated greenhouse very late in the fall, around the beginning of December, and take them out in late March. Mind you we are in Atlantic Canada and do not get extreme temperatures. My only worry with putting these plants in the greenhouse over the winter is that they will overheat so we are going to watch the themometre if we get unusually warm winter weather and open the greenhouse doors when needed. The other thing we will do is simply leave plants outside in a protected area, these will be the most hardly varieties of course. Hope that helps. DON'T USE STRAW!

I see a lot of perennial growers in Ohio put the pots tight together in long rows and in November cover them with white plastic stretched over the top, and held down with cinder blocks around the perimeter. This seems to work well for many varieties, but with 2 caveats. Make sure they are well watered before covering, and use plenty of rodent bait under the plastic. Voles and mice will get in there and cause lots of damage.

You can get information on this for your area from your County Extension Agent or the County Co-operative Extension website in their publications.

Planting plugs in the fall so they are more ready in the spring is called "vernalizing". Jolly Farmer gives these directions for doing that (although in a greenhouse setting):

"Growers can vernalize their own pots if desired. Plant early...December or mid-January using 288Âs or 144Âs. Once the plants are well rooted & crowns developed, temperatures should be lowered to 35 - 40 for two weeks, then lowered again to 28 - 30. Vernalize for 8 - 12 weeks. Ship in spring when plants are ready."

Two layers of ordinary blue tarp. With diverse kinds of mouse poison underneath, inserted in cut pieces of 1 1/4" black poly water pipe.

I have the whole nursery laid out to fit the 40' x 60' tarp. (Which is really about 38' x 56').

You roll up standard cement blocks in the edges.

If you can plan your terrain in advance, make each 40' x 60' section slightly domed in the middle so that water won't puddle.

superphosphate, this is interesting to me because you are in NH, almost in my zone (probably below the Notch), and you have a nursery which means you do have experience in this.

Now I have questions. :) What size containers or plants are you talking about protecting? Is this B&B trees and shrubs or perennials in plastic pots? If pots, what age are the plants and are you just placing them pot to pot or laying them over? And I take it you have the ground covered with the black ground cloth?

"With diverse kinds of mouse poison underneath, inserted in cut pieces of 1 1/4" black poly water pipe."

So you put the poison in the pipe so the mouse goes in there and dies? What is 'diverse kinds of mouse poison'...things like peanut butter and de-con? :)

With this method and not using all the expensive foam insulated blankets & white winter poly how much loss do you suffer? And you keep nothing covered up inside a hoop house?

The domed terrain is a good tip. Thanks.