Garden Zone Confusion

It’s early March here in the north Idaho panhandle. Time to start seeds for the garden, right? I look across the yard and see my six year old daughter climbing a tree. That tree that she could hardly reach the branch in the summer is practically a bush with three feet of snow around its trunk. It’s time to figure out what is suggested for our gardening zone.

Hardiness Zone: 6!?

What is a hardiness zone and how does it apply to my garden? The coldest temperature possible for my region is not what determines the hardiness. From what I’ve read, this may be determined as the average coldest temperature it has been over the last thirty years. The map puts me in a dark green area, called zone 6, and says it gets down to -5 to -10° F regularly. Yes, that’s true, but other more southerly areas get those temperatures without the snow load I have. And, what about the coldest possible? I looked that up and it can get to -30°F in the colder winters.

 After seeing the news about the freeze that went through the Eastern and Great Lakes states this winter, I’d like to make sure my perennials are grown for that sort of hardiness. 

Another consideration will be with the frost dates. Most tree fruit needs a certain amount of time to grow and ripen the harvest. If the tree blooms too early, there won’t be pollinators out yet, and a frost is likely to wipe out any fruit that is set. 

Frost Dates? May 21 (last), September 19 (first), about 120 day growing season

Zone: 3 !?

The zip code I have to use tells me the local city’s frost dates. The city is bordered by a lake which probably helps to even out the growing climate. The locals refer to our area as “the snow belt” because it receives more snow. We will be dealing with ice and have snow still hanging around, hopefully melting, long after the city is clear of it. And, we’re not in the mountains. From what I’ve observed, our last frost date is on average closer to June 1, and our first frost comes early September. Locals love to share about the time it snowed on the Fourth of July. The tomatoes don’t like the chill in the air by the end of August, and rarely last past September 10. That’s closer to 100 day growing season for the heat tolerant plants. There’s a separate map for this! This map is not the one on the seed packets! This is the frost date based climate zone I need to know for my garden.

Zone 3.