Aster Lane Edible defintion of hardiness (Canadian Zones)
Very hardy: Shown to grow in very cold temperatures and a wide range of conditions. Found in prairie gardens for example. Approx. Zone 3
Hardy: Grows here well. We are Zone 4b
Borderline Hardy: Will grow under ideal conditions most years or with protection. Approx. Zone 5/6
Half tender: Will survive below 0C temperatures but cannot survive maximum cold temperatures in this region Zone 7 or higher
Tender: Frost tender
Instead of using zones in our descriptions, I've chosen to take inspiration from the UK classification of hardy, half-hardy and tender. There are so many variables affecting a true description of hardiness, especially for herbaceous plants, that I am leery of giving a zone. That said, Canadian zone designations take multiple factors into account.
-- Plant Hardiness Zones in Canada --
My observations of hardiness
Hardiness is a hard thing. It depends on a multitude of factors including what it is grown in (shallow, deep, light or heavy soil), where it is grown (slope, water table depth, shelter, proximity to other plants, and buildings), growth habit (thickness of stems, roots, evergreen or otherwise leaves), temperature (low point, freeze-thaw/oscillations, sustained low temperatures), other climatic factors (wind, other stressors), age or growth status when overwintering (how big is the plant, how old, how new is the growth) and type of plant (cultivar, etc…). We estimate zones based on where it is native but also where it is found growing. If you look at the literature, you will sometimes see discrepencies with one source saying it is much more zone hardy than another. It could be that one population is more cold hardy or flood tolerant etc… than another. When growing a borderline plant, it makes sense to try and choose seed parents that are growing in a similar environment to yours to maximize success but recognize that some borderline plants will be winter-killed in hard years. After all, zones are also about averages.
And, just because a plant can survive your climate does not necessarily mean it will thrive or that it will flower or fruit. It may be day light sensitive therefore not flower until near the fall equinox when things are starting to freeze or it may require more heat units to ripen fruit.
Your own microclimate may or may not be favourable to a particular plant either. You may have a wonderfully sheltered alcove that grows the best peaches but your more open gardened neighbours fail, or your soil might be too low, heavy and cold to get good sweet potatoes.
Failure with a plant may also have nothing to do with zone but be because of particular pest or disease pressure, inexperience, absence of pollinator or the wrong growing conditions like soil pH.
Then again, growing a plant out of its usual area may mean that there aren’t any pests or diseases that have discovered it so it is carefree. It may also mean that it is invasive.
So should you grow the plant? I’m an experimental gardener. I try to avoid anything blatantly environmentally problematic. I don’t encourage garlic mustard for example. When it comes to hardiness, I push the limits. As many a gardener’s mantra is “You never know until you try.” Besides, by sourcing from promising seed parents, you might get something special.
All about growing, selecting and using edible plants in the Ottawa valley.