North American Fruit Explorers mailing list at ibiblio

[dwoodard@becon.org]

Regarding apples, what I have read suggests that there is no gain in
maximum hardiness with a hardy rootstock, however there may be a gain from
earlier entry into dormancy and later exit from it. Coldhardiness is not
an absolute but increases from the beginning of dormancy, reaches a
maximum typically in mid or late January (if memory serves) and then
declines. The shape of that curve of coldhardiness against time can vary
considerably with cultivar.

Decades ago it was reported that in an orchard in New Brunswick province
in maritime Canada, the cumulative yields of certain marginally hardy
apple cultivars were drastically increased by topworking them on a hardy
framebuilder, apparently because only the outer limbs would be damaged by
extreme cold, and they recovered quickly when most of the tree was
unaffected.

An ironclad hardy rootstock would presumably have a similar but weaker
effect. A rootstock that takes winter damage will affect the whole tree
adversely. The susceptibility of rootstocks to winter damage will vary
with snow cover.

The late Percy Wright, a horticulturist, amateur fruit breeder and NAFEX
member from Saskatchewan, reported the observation of a Canadian
orchardist that the survival of peach trees in an Okanagan orchard subject
to cold spells was enhanced by topworking them with a branch of
prairie-hardy cherryplum.

Doug Woodard
St. Catharines, Ontario, Canada


> I know there was some discussion of this before in a broader context. But
> I was wondering besides citrus and mabe apples, does anyone know of any
> other plants that can increase their cold hardiness by the choice of
> certain rootstock?
>
> robert
>
>
>
> --------------------------------------------
> Now Zone 8a!!  Atlanta, GA