Alaska Pioneer Fruit Growers Association

INCREASING APPLE CULTIVAR HARDINESS TO -40° F

December 9, 1994

 

—by Bernie Nikolai

14012-86 Ave.

Edmonton, Alberta T5R4B2

 

(Reprinted from Pomona, v. 25, no. 4, Fall 1994, with permission)

 

For about the last five years I’ve been experimenting with attempting to significantly increase the hardiness of tender apple cultivars to enable them to survive and produce after prairie Canada’s long, very harsh winters. This past winter was the coldest in the past decade, with a minimum temperature reached on February 7, 1994, of -40°F (also -40°C). This temperature was in the city of Edmonton. Outlying areas were several degrees colder.

 

The winter was so cold that the only Nanking blossoms I had were on the branches that were protected by the snow. The bushes looked a bit odd with heavy flowering to the 18 inch from the ground level, and then nothing. This only happens in our most severe winters. Despite the Siberian-like weather, an astonishing number of relatively tender apple varieties not only survived, but also flowered heavily and are developing fruit as I write this, in late June of 1994.

 

The following varieties, none of which are supposed to thrive and live in our harsh Zone 3, borderline Zone 2 climate, survived, and were fully hardy to the tips of the branches: Akane, Ariel, Ashmede’s Kemal Discovery, Fameuse, Ginger Gold, Grushovka of Moscow, Honey crisp, Honeygold, Idared, Jerseymac, Liberty, Lobo, McIntosh (MacSpur), Novamac, Oberle, Paulared, Sandow, Splendour, Summerred, Vista Bella, and Wealthy. The only varieties that froze back at all were Red Melba and Jonagold. However, even the remaining surviving Jonagold had blossoms and is developing fruit.

 

You might think this is a fluke, hut let me assure you I have been fruiting many of these varieties for the last four consecutive years. However there is a “secret” method that will enable these varieties to prosper, and you absolutely must use it or they surely will not survive in harsh winter climates such as central Alberta.

 

The “secret” method is top working the tender variety to a prairie hardy tree. Studies have repeatedly demonstrated the least hardy parts of a tree are the roots, the lower trunk, and the crotch angle of branches where they come out of the main trunk. If you bypass these tender-portions by grafting the tender varieties onto the hardy frame tree branches about six to twelve inches or so from where they come out of the main trunk (on a Dolgo Crab, for example), you may be astonished as to what will survive and produce for you if you live in a cold climate.

 

My rootstock is Mains baccata, the Siberian Crab, and the hardy frame trees are Rescue, Dolgo, Norland, Battleford, and Selkirk Flowering Crab, So far I have no recommendations as to which hardy frame tree is best They all seem to work equally well to date. I have noticed that horizontal grafts are hardier than vertical grafts especially when tender apple varieties (i.e. Jonagold) are used. My belief is this is caused by the slightly lesser amount of fall growth and earlier dormancy of horizontal branches vs. vertical branches.

 

You may have heard that Siberian Crab is a poor rootstock to use, due to a lack of compatibility with many varieties. This is true with the more “developed” apples, but not with our prairie hardy Canadian apples, most of which have a good deal of “crab” in their recent ancestry. My trees are basically hardy frame trees on Siberian Crab rootstock, with the tender varieties top worked onto the branches of the frame tree.

 

I also use Ranetka Crab, which seems equally hardy in our climate, and has better compatibility according to reports (although I personally have not had any compatibility problems using Siberian Crab with a prairie hardy frame tree). I have a hunch that Ranetka imparts more hardiness to grafted-on varieties than Siberian Crab. As an example Goodland, a marginally hardy apple here if grown on its own trunk, frequently dies back is grown on baccata or Columbia Crab roots, but seems fully hardy to the lips of the branches if grown on Ranetka.

 

The late Percy Wright, a horticulturalist of some note in Prairie Canada, once related a very interesting story of hardiness with regards to peach trees in British Columbia’s Okanagan valley. His uncle from Saskatchewan had moved west to the Okanagan and for sentimental reasons had grafted some ultra hardy Saskatchewan plums onto a few of the peach trees in his orchard. A harsh test winter arrived after a few years which decimated not only the peach crop, but also the trees themselves. Most were killed outright or at the least severely injured. However the peach trees with ultra hardy Saskatchewan plums grafted in the branches had no winter damage whatsoever! Percy Wright theorized that the hardy plum grafts had caused the peach trees to go dormant earlier, and thus not be harmed by the severe cold, which occurred early in the winter that particular year. If you have hardiness problems with peach trees in your area, try it. Perhaps this is what is required to give your trees that extra bit of hardiness.

 

If you have a favorite apple tree that dies back after cold winters (that isn’t topworked), try grafting a branch or two of hardy crab onto it. Some of the tender varieties on my trees are “sandwiched.” By this I mean not only are they topworked onto a hardy stembuilder or frame tree, but also the tips of the grafted branches are themselves grafted. As an example I have a McIntosh grafted onto a frame tree of Battleford, and the tips of the McIntosh grafted again with a hardy crab, Dolgo. I haven’t found this necessary, as the topworking alone seems to give the required hardiness. However, in an even more severe climate, “sandwiching” just might be an improvement in terms of promoting hardiness over topworking alone.

 

Common sense cultivation practices are also required. Specifically never fertilize your topworked trees past the first of June as you risk late fall growth which will often winterkill. If you apply manure to your trees, do so only in late October or November. Manure is a slow acting fertilizer, and if you apply manure in the spring, you will probably get late fall growth, and possibly have tender grafts severely damaged by the winter as they won’t be fully dormant when they should be. Also don’t water past about early to mid August. If you do, late fall growth may also occur, which is highly susceptible to winterkill. The only exception is to really soak the roots well after the trees are fully dormant, but just before the ground freezes solid, about the first week of November here. This seems to keep the trees from drying out during the winter, as well as creating a ball of ice which delays the trees in leafing out too early in the spring. Also wrap the trunks to prevent sunscald and rodent injury.

 

Dwarf apple rootstocks are being tested with surprisingly good success in our harsh climate. Ottawa 3 has survived for 15 years at Vega, Albert. The trees are grafted with Rescue Crab, and were not staked, irrigated, or protected in any way. They were even planted in a grass field with grass growing right up to the trunks — a definite no-no.

 

After 15 years they died out, but I’m not sure they would still be alive if normal cultural practices, i.e. irrigation and noncompeting ground cover were employed. I’m also aware of a number of Goodland trees that have done very nicely on Ottawa 3 rootstock for the past eight years, growing in central Saskatchewan, zone 2.

 

My test trees on Mark, P 22, and Ottawa 3 (mainly State Fair and Sweet 16) all survived -48°F conditions this past winter in my test orchard east of Edmonton. There was about 18 inches of snowcover this year (winter 1993-4). This temperature killed the Sweet 16 and State Fair above the snow line, but the rootstock was line and the trees arc aggressively sending out new leaders. This is the first year I’ve had hardiness problems with Sweet 16 or State Fair. Both survived -42°F last year and were fully hardy to the tips of the branches. It seems the killing temperature for these two hardy varieties lies between -42°F and -48oF.

 

If you live in a severely cold climate, try Ottawa 3, P2, or P22 if you’re looking for a dwarf apple rootstock. All should do well for you, especially if you irrigate the trees, eliminate competing ground cover, and stake them.

 

The next group of dwarf rootstocks hardy enough for the prairies, would be Mark and Bud 9. However, I would be more comfortable with Ottawa 3, P2, or P22 if you are just starting out in your experimenting. In tests this last winter just north of Edmonton (- 45°F), both Mark and Bud 9 died down to the snow line (these were totally ungrafted rootstocks), but Ottawa 3 ungrafted rootstocks survived above the snow line, with about 6 inches of tip dieback.

 

A new Russian semi-dwarf rootstock that has potential for our cold region in Budagovski 490. This rootstock is self- supporting, precocious, induces flowering in the grafted-on variety in the third year, and both the roots and branches of Bud 490 are fully hardy at -40°F, according to reports out of Wisconsin this last year. According to reports I’ve heard, about 50% of the dormant scions will root if they are simply put out vertically into the earth with a few buds sticking out of the ground and the soil kept moist. Instant rootstock for next year’s grafting! I experimented this year with trying to root dormant cuttings of Bud 490. I dipped the budwood in rooting hormone, stuck the sticks below the soil, kept them moist, and had 100% successful leafing out! However, after a few weeks, the leaves withered and died. If you have had any success in rooting cuttings of Bud 490, please drop me a line and let me know your methodology. Time will tell if this promising rootstock is suitable for our conditions. I personally believe a commercial orchard of commercial quality apples (assuming they are early to mid maturing) is possible in prairie Canada, providing the trees are topworked to hardy stembuilders. A friend with a small commercial orchard topworked some of the varieties I’ve mentioned in this article to some of his trees near Carmen, Manitoba two years ago, and they all survived fully and are fruiting for the first time this summer (1994), despite -40°F (with wind) this last winter.

 

However, in tests last year these same varieties that did so well when topworked, died back severely when grafted directly at ground level to hardy Siberian crabs. It seems the lower trunk and branch crotches angles coming out of the main trunk absolutely must be of the hardy variety for these .tender apple cultivars to survive temperatures of -40°F or colder.

 

Granted, you would have to want a cold climate commercial orchard pretty badly to spend the time and energy in topworking a thousand hardy apple trees! Perhaps the best application is for the keen fruit grower who wants a few backyard trees for his own use and enjoyment, and who wants to grow varieties normally impossible in their severe climate. Try top working if you live in a severely cold climate. I can attest to the fact that it really works!