Increasing growing zone by 1 or more zones - currently in zone 4a

I'm looking for recommendations from those who have tried and true success at increasing their growing zone. We are in zone 4a of MN (USA), but would love to plant some edible fruit and possibly even nut trees that are most suitable in zone 5 - zone 6. We've read of what Sepp Holzer has done to increase his zones, but I'm wondering if there are any in a similar zone as ours that have had success doing the same and how they did it. We have 20 acres, but much of it is sloped from 4 degrees to about 40 degrees to the North. We are slowly incorporating a variety of permaculture designs into our homestead where our aim is to be growing nutrient dense, beyond organic foods with a longer term goal of becoming self sufficient on the land that we have. We've done plenty of experimenting, but would hate to invest into trees and loose them if there is a way to avoid it. The fruit trees we have planted thus far (suited for our current zone) are doing quite well, but would love a bit more variety.

Therese,

Are there any particular techniques you're interested in trying? What experiments have you done, to what effect? If you can share some specifics you might get more specific answers.

One traditional technique in northern Europe is using masonry walls to retain solar heat (and block winds) but that might be too much work on a large scale.

We are in the southern Red River Valley, so also Zone 4a. But just as important is the fact that we are in heavy clay which can be an impediment to growing certain trees and shrubs that do just fine a few miles east of us on the shoreline of the old glacial Lake Agassiz. Some recommendations would be to look at releases from the University of Manitoba, much of which will be adapted for even farther north and for clay soil, but also something like Bergeson's Nursery [ https://www.bergesonnursery.com/index.html ], Sheyenne Gardens [ https://www.facebook.com/sheynnegardensharwood/ ], and information from NDSU's Carrington Research Center: https://www.ag.ndsu.edu/CarringtonREC/northern-hardy-fruit-evaluation-project .

One possible source for hazelnuts: http://riverbendhazelnuts.blogspot.com/

All of the above are sources for stock that will grow within 4a. For trying to grow more warm-weather stock, certainly whatever sepp holzer and others have mentioned, but additionally a dense, north-side wind-break can help reduce tree and shrub mortality. And I think for the most part, many of the nuts and fruits do not like to have wet feet, with the exception of some Viburnums and perhaps a few others.

I'm in MN, I have some suggestions.
First, you should know we are warming faster than the rest of the country, we'll be zone 5 in the southern half of the state soon in my opinion.
I am an experimenter, I love to try to push growing zones. Some plants and trees do better than others.

Things like peaches, medlars, goumi, american persimmon, sweet cherries, paw paw, hickory, and pecan are marginal so far for me. They all grow, some well, some die back and resprout taller each year, others have had dieback years and slowly recover. I've only truly seen a few things die for me: a Contender peach that grew for 4 years and died after the horrible 2013 winter, a few maypops that I started from seed, a Kousa dogwood(2013) and a handful of paw paws.
I would try a few things:
-Start things from seed. It's cheaper for large numbers of plants, and there's a chance you could find certain genetics from seedlings that impart some cold tolerance. Graft if you want onto these, but those seedling roots give you a chance to grow things back if they die back to the ground.

-Find microclimates. South sides of buildings, rock piles, under pines, look for areas that stay frost free early in the morning after a frost.

A few species you may not have tried:
Seaberry, grows great and doesn't care about the cold.
Bush cherries do really well too.
Serviceberries
I have one Paw paw from Jung seed, a seedling that has lived through that 2013 winter and seems on its way to thriving now. I think with Paw paws it's the first few years that matter, they grow slowly and need to be out of hot sun, but they also have really deep roots and can handle the cold ok.

Arctic Beauty Kiwi will do better than Arugata hardy kiwi.

Antonokova apple rootstocks seem in some ways just "tougher" to me than some of the semi dwarf or dwarfing rootstocks. I grew a bunch from seed and was impressed by their vigorous roots, growth in cold fall weather, and overall hardiness.

-Oikos tree crops has a bunch of interesting fruits and trees, I love their stuff and they try to select for cold hardiness and overall health in their stuff.

Wild plums and other shrub plums have just exploded for me, they seem really well adapted to the cold and taste pretty good too.

Good luck!

Steven - I'm open to any techniques that are tried and work, while understanding they may not work at our place. We've tried some planting around large rocks/boulders with some success, but our experimentation has been in the garden spaces instead of with trees. We have planted around 10+ fruit trees over the past 4 years, with a couple of losses. They've been planted in different areas some receiving more sun, others closer to water and in the shade until later in spring when the sun rises higher in the sky. We did this to experiment with keeping the trees from blossoming too early. The ground wasn't the best in this area, but the trees that did make it do bloom a bit later which could be helpful for late frost. The trees that have done the best are planted using the Ellen White Planting method that we learned about from an organic gardening workshop we hosted. The speaker shared about this method. The trees we planted using this particular method did extremely well and bore a great deal of fruit in their 2nd season. So much so that the branches almost broke. This particular method though doesn't help with zone temperature, but is focused on nutrient dense growing for the roots.

Methods we've tried growing within the garden spaces have been using hot spots/microclimates that are naturally occurring on our property in permaculture zone 1 and zone 2 where we plant the most items. Planting around large rocks/boulders. We have a lot of small boulders that we could use to build up around trees, but it would take a huge amount of effort to move them since we have little machinery to help. Before we do this I'm still not confident in how to best do it around trees. I haven't see how Sepp Holzer does this method in great detail. We have tried and had great success with hugalculture raised beds. People who come to our place are always amazed at how well veggies grow on these raised beds and I think part of the reason things do so well is because of the increased soil temperature early and late in the season. The heavy mulch/Back to Eden approach has also been tried and did not go well for where we live. Our soil temperatures stayed far too low and it took 3 years to get the wood chips to really break down. In the end we removed what was left and put them in a section of the garden that we weren't using to let them fully break down. Love the idea of Back to Eden, just not the best for our cooler climate and moisture level. We have no walls to plant along, although dream of creating some stone walls down the line. I'm not sure of other methods that can be used outside of greenhouses/high tunnels for trees or large bushes.

Russell - thank you for your thoughts. I was just researching seaberries and serviceberries. We have growing and doing well thus far raspberries, elderberry, currants (we'll know how well these did this spring), apple, plum, sour cherry, and apricot along with lots of different medicinal herbs and perennial edible plants. Each year we'd like to continue to expand the edible items and nut trees would be a wonderful blessing, along with a couple more varieties of fruit.

John - Thank you for the links. Great resources and have spent the last hour perusing the websites.