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South facing sites are difficult. Cold air, already not containing much moisture, is warmed and it's relative humidity drops even further. So evergreen needles/scales and tree buds dry out. The roots are frozen so can't make up the deficit. Reflection off of snow in late winter makes the situation worse.

It's not just the degree of cold, but the length of the winter, and the number of hours of sun. In Alberta we have about 2000 hours of sun per year, but have below freezing temperatures for about 6 months. (Our annual average is something like 6 C. No permafrost, but by February, you wonder...)

What trees/shrubs are candidates to use close to the south facing house in a zone 3 climate with about 6 months of below freezing temperatures. Candidates should have height to width of 2:1, and have heights that reach 7 to 15 feet.

So far I have found some success with Rocky Mountain Juniper, and common lilac.

In the answer please specifically address south exposure. I know of many shrubs hardy in zone 2 and 3, but few that will tolerate the above freezing air/frozen roots, 25 C variation between day and night temps of a living next to a south facing wall.

The following do NOT work:

Any of the cultivars of eastern white cedar. (T. occidentalis) such as Techna, Brandon and Skybound.

Any of the very compact spruce. Fat Albert, Nana. Small spruce even in the open tend to sunburn anyway on the south and southwest sides in late winter from direct and reflected sunlight. Compact spruce have more still air near the needles, and dry out more.

Mugo and Mountain pine seem to tolerate the winter warmth, but mugo is hardly upright, and Mountain typically gets 25-35 feet tall with time. Both species (Taxonomic lumpers consider P. uncinata to be a subspecies of P. mugo.) are highly variable from seed, with larger mugo grabbing at the eavestroughing.

Ninebarks generally have a bad rep in cyclic temperatures. They do well in the open in the Edmonton area, but have a lot of dieback in Calgary with it's frequent chinooks, and winter thaws.

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You might be interested in a publication (#1286) by the Research Branch of the Canada Dept of Agriculture compiled by Sherk and Buckley "Ornamental Shrubs for Canada" 1968. It has a list of shrubs of all kinds from Acer ginnala to Weigela "Manchurian Pink" noting details such as height and hardiness zone. It has select lists by fragrance, moist/dry, acid soils etc but unfortunately no list by hardiness so to find a hardy shrub it's a case of thumbing through. Selecting from the dry list, we find among others Potentilla fruitcosa, Physocarpus opulifolius and Rosa setigera. See if your local library can find a copy you can borrow. My copy has heavy glossy paper so it's not the kind of book easily worn out by reading.

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I can recommend a few shrubs, most of which are relatively tall for anything close to a house:

  • Any of the ninebarks (Physocarpus opulifolius). These include the cultivars Summer Wine, Diabolo, Little Devil, etc. Note that this species' normal growth habit is vase-shaped, and that they do NOT like shearing. In fact, they look very sad and relatively ugly when trimmed. If you're planting next to a house, your best bet may be the Little Devil cultivar (4' x 4'), as it's more upright than vase-shaped. The other cultivars would look nice in a bed at the corner of the house.
  • Most Arrowwood viburnum (Viburnum dentatum) cultivars (Blue Muffin, for example). These varieties tend to be more oval/globular than true uprights, and some can sucker a bit.
  • Most if not all Eastern Red Cedar (Juniperus virginiana) cultivars. The species itself is hardy to at least zone 3, and so should most cultivars (I used to sell the Skyrocket cultivar as a zone 3, although I now see that some sites show it as a zone 4. Regardless, I personally have experienced this cultivar surviving at -31 F in full sun)
  • Juniperus scopulorum 'Wichita Blue'. This is a wider shrub with a distinctly blue cast to the needles. A very pretty variety.

From my own experience in the nursery trade, I urge you to purchase only Northern-grown cultivars of whatever shrub you purchase. Those grown in Ohio and Oregon (or points farther south) are not as hardy (per zone) as those grown in Minnesota, Wisconsin, or Michigan. Also, with the evergreens, keep them well-watered in the autumn up until ground-freeze in order to prevent winter-burn.

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  • I wouldn't call ninebark upright. Vase to globular to sprawling. Eastern white cedar is what brought this up. They cook on south exposures. The south half of the shrub is fried. – Sherwood Botsford May 2 at 13:39
  • @Sherwood Botsford - the species Physocarpus is definitely vase-shaped; it's also 12 foot high at maturity and almost impossible to find commercially. I was referring to the cultivars, which are vase-shaped as I noted but much better behaved. Note that I recommended the cultivars for corners and the 4x4 cultivar as a foundation planting. – Jurp May 2 at 14:07
  • I don't know the exact conditions. The client asked for something he could plant 3 feet from the foundation that would grow 15 feet high and not touch the house. – Sherwood Botsford May 3 at 22:55
  • So - 4' wide by 15' high (leaving a foot of literal wiggle room). Possibly/probably impossible. Here's an example - I planted Emerald Green Arbor Vitae as as screen between my house and a neighbors. Dimensions are supposed to be 4' wide by 12'+ high. They're currently 3' wide and 6' high. I know of others that are 5' wide and 10' high (zone 5). I had a Techny Arb that was 8' wide by 15' high (taller and wider than it was supposed to be). Lots of variables with sizes (fertility, water, etc.). You could try a Skyrocket Juniper (a little shorter and possibly wider than desired). – Jurp May 4 at 2:32
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I have seen red twig dog wood growing well north of Edmonton ; very red bark . And spruces ( Alberta, white and black). And a white barked birch but I don't know which one. As I remember , mountain ashs were planted in Edmonton ( showy red berries.) .I just remembered the location, West Whitecourt ( I would guess the garden zone is about 0 ).

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  • Dogwood hardly counts as upright. – Sherwood Botsford May 2 at 13:37
  • birch gets suckered by chinooks and warm spells in the foothills. I woudn't expect it to do well on a south wall. Do you have experience with it in +10C air with frozen roots? – Sherwood Botsford May 3 at 22:54

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