You are most certainly pushing the envelop with a zone 4 :-) But it can be done.......just realize your chances for long term success are not exactly high.

'Red Dragon' has a reputation for hardiness. Of all the laceleaf forms, this seems to have the greatest rate of survival in colder climates. Do not let its delicate looking foliage fool you - most of the dissectums and especially the red leafed forms are very tolerant of sun and are very tough little trees.

You want a situation out of winter wind and with some protection. Reflected heat from the west or south side of a structure or from bordering paved surfaces is a bonus. Very well-drained and acidic soil. JM's grow very well with a wide range of plants - just combine with things that do not require division or frequent cultivation as the trees dislike any root disturbance.

Top growth on Japanese maples is able to tolerate colder temperatures than the roots. From Vertree's text: "The exposed parts of most Japanese maple cultivars, once established, can withstand winter freezing and air temperatures down to minus 18 degrees Celcius (0 degrees Fahrenheit) and below. The roots, however, can only survive to minus 10 degrees Celcius (14 degrees Fahrenheit)." Winter mulching might be in order if deep soil freezing is anticipated. Be sure to keep any mulch well away from the trunk.

One other thing I have noticed that seems to help plants in winter is steady temps. Wind can be a problem but so can sun in my view. If the plant is shaded in winter it wont experience the great fluctuations in temperature that the sun can cause. I repeatedly over wintered young Japanese maples in a shaded area protected from wind and sun above ground in 1 gallon pots with only oak leaves around the pot for insulation and never lost a plant here in zone 6 and we have gotten to at least -10F on a few occasions.

You may also want to consider Acer Japonicum Green Cascade. Many report that japonicums are hardier than Palmatums

I agree with picea about having it shaded in winter. In addition to the reason mentioned, this also helps slow down bud growth keeping them dormant. Doing so makes it less likely to be nailed by a late frost in spring. Mulching heavily, as ggal mentioned, cannot be overstressed in zone 4.

tj

In the Minneapolis area (borderline zone 5 in the urban areas), the usual recommendation is to not put them up against the south side of the house for the reason mentioned above, early wake-up.

Thanks everyone

My winters are generally "stable" temps. IF its a warm winter, the temps generally are stable, same with an everage or cold. The temps dont swing like Calgary, for instance (although, they do sometimes,weather isnt perfect :P )

I do have a space where it could go, north side of a fence, about 7 feet away from a south wall. It should get the wind blocked, as well as stay in the shade. Same general spot as a Fargesia I planted, hostas, mock orange and my Helikkii RHododendron.

OF course I would mulch. That makes all the difference here, same with the snow (which its insulation/mulch all in itself). The thing is to, the south wall of my house should be shaded with an apricot tree, but that wont be for a few years.

Thanks everyone!

You have very sound growing advices from the above posts. As far as survival go, it is still a mystery to me (after playing with lots of maples for more than 20 years). I planted 3 Japanese maples at my Zone 4 cottage more than 10 years ago for experiment (1 Bloodgood and 2 root stock). One was eaten by deers. Two survive well but their heights never exceed more than 3 feet. They are all planted in the worst possible conditions for most Japanese maples; full exposure to wind from the lake, full sun, almost pure sandy soil.
I am curious to know how many years you have your Red Dragon and Fargesia, and what variety is your fargesia.

I just bought the Red Dragon, it isnt even planted in the ground yet. I have Fargesia Rufa, which I bend to the ground, bury it in leaves, then throw a tarp on it. The snow does the rest. Its been here 4 years, next year will be 5!

Next to a safe facing wall is not ideal. The plant will warm up on warm winter days and then get frozen at night when the sun drops. This will reduce the cold hardiness of the plant when compared to one that is in another location not subjected to the warming/cooling stresses on sunny warm days in January.

I would plant a Korean maple (Acer pseudosieboldianum) or one of the trifoliate maples (Acer triflorum, etc.) if I was looking for long term success with these trees.

The Japanese garden that I work at is technically zone 4 (old zone map), but is in a river valley protected and is on the edge of Zone 5. We have plenty of Japanese maples that never experience winter damage. So if you want to give it a try go for it. With global warming, hey you might be OK, just don't put them too close to the wall.