What's A Zone?

galetta@sympatico.ca, (613) 797 6257

updated May 2018 Home Map

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Galetta Rose Nurseries

closed for the

2018 season

rose growing information index

What's A Hardiness Zone?

All the roses in the nursery are marked with a single number that represents a "hardiness zone" -- a simple way to describe how well a species will survive our climate. The zone represents the average minimum winter temperature: Ottawa is in Zone 5, the Upper Ottawa Valley is in Zone 4.

The lower the number a plant has, the hardier the plant. Any rose marked Zone 5 will usually survive the winter here; Zone 3 and Zone 4 roses are even more hardy. But, some Zone 5 plants and all Zone 6 plants will have a hard time surviving, even though they may thrive in Kingston or Toronto or even in Perth. [If a rose won't grow here, I won't sell that variety]

You can get some idea of how the growing seasons differs in this area from other parts of Ontario:

 
 Toronto
Ottawa
Ottawa

Valley

Average date of last frost
April 25th
May 15th
May 23rd
Average date of first frost
Oct. 15th
Sept. 30th
Sept. 24th

What plant zone are you in??

Note: if you're looking at "zone maps" from the US, remember that they use a different system than in Canada. Typically, a Zone 4 plant from a US source will be a Zone 5 plant in Canada. A Zone 5 plant in the US will be a Zone 6 plant in Canada.

Survival of plants is affected by many factors in addition to low winter temperature "zones":

  • freeze-thaw cycles during the winter often cause more damage than consistent cold temperatures.
  • snow cover has an insulating effect on plants: lack of snow cover can result in damage.
  • sun scald in late winter can crack the bark of many roses
  • late spring frosts can damage many plants, especially those that tend to put out buds early in the spring. Late frosts will rarely cause a hardy rose to die -- it mostly affects the early bud growth.
  • exposure to strong winds will kill some plants and cause unsightly discolouration on others
  • frost in low-lying areas can delay the onset of growth in the spring: for example, the nursery in spring is typically 2-4 C colder than the fields 50 meters away.
  • road salt and pollutants can have a major effect on winter survival: rugosa roses are very tolerant, while others will succumb to salt spray even during mild winters.

With so many factors affecting how well plants thrive in our climate, it’s difficult to specify exactly how a particular plant will do in a specific planting site. The "zone number" is a good general guide to hardiness, but if you have questions about a particularly difficult site, please feel free to ask me. I do indicate on the rose labels which varieties are particularly suited to difficult growing conditions.

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