One question that always stumps me is "What growing zone is Alaska in?" Funny thing is (well, to me), it's a question I get all the time. New gardeners are always confused by the idea of USDA hardiness zones. And, of course, these is always an interest shown by Outsiders who wonder what it is like to garden up here.
First of all, what is all this growing zone stuff about? This is the simple part. The United States Department of Agriculture produces a map that shows the annual minimum winter temperatures an area experiences. This map is divided into 10-degree zones, starting at Zone 1a (minus 60 to minus 55) moving up to Zone 13b (65 to 70). (Yes, I said in segments of 10; there is a Zone 1b and 13a).
Given its size and different climate regions, Alaska doesn't have just one zone, as you would imagine. We cover the gambit all the way from Zone 1b up to a balmy 7b, a spread of 65 degrees (minus 55 to 10 f). If you want to know exactly what your area's zone is, check out the USDA's map, which also comes in an interactive version on their website.
If you live near me in South Anchorage, your zone is 4b. This means that the average minimum temperature my plants are likely to experience is a chilling minus 25 to minus 20 degrees. If I am not mistaken (and, I sure hope I am not tempting the powers that be here), this is way colder than it's been in my neck of the woods for years.
Some of you relative newcomers to Southcentral may not even remember ever seeing the winter temperature that low here. What gives?
Well, first of all the USDA Plant Hardiness Zone Map is updated periodically. Still, the last update was 2012, only a few years back and I can't remember experiencing minus 10 degrees during that time, though the memory is selective about these things. You could chalk this up to it being a map maintained by the government: They know it pays to be a bit conservative when it comes to telling folks what plants they can expect to survive a cold winter.
No, there is something else here. The "average" in average annual extreme minimum temperature is the average of all the winters for which the USDA has records. In that case, pre-global warming readings easily cancel out our now-warmer ones. Early readers of this column remember plugging in cars and much, much colder winters.
Here is the point. There are really two important things when it comes to hardiness zones and gardening in Alaska. The first is obvious: Are there going to be enough days above freezing to grow crops and annuals? The zone map is only a general indication. Warmer zones have longer summers. And our zones have been getting higher. This makes sense. When records were first taken in Talkeetna, summers were only 60 days or so long. Today they are well over 120 days.
Most seed catalogs and packages will list the number of days it takes for the seeds to germinate and produce flowers or fruits. If not, look up the plants you want to grow on the Internet. You guide should be around 120 days, but remember that comes from an optimist who might even shoot for 130 days given the weather of late.
The second important thing has to do with perennials, trees and shrubs. This is where the USDA hardiness zones really come into play. Again, plant labels and catalog offerings should list the hardiness zone of any given plant.
Again, that doesn't mean you can't be a bit of an optimist. Given the recent warming trend of our winters (our yard in South Anchorage feels more like a 6a these days), you may be tempted to update the zone map on your property and plant a bunch of things that usually grow in warmer zones. (This belies the idea of sticking to natives, I know, and merits very careful consideration first.) Just know that while you may end up getting away with several years of warm-climate trees, there is a really good chance a hard winter could still take them down. If that happens, don't blame the government.
Jeffs Alaska Garden Calendar
Alaska Botanical Garden Annual Meeting and Reception: Learn what is going on at the garden. 7-8:30 p.m. Wednesday, March 2, at the BP Energy Center, 900 E. Benson Blvd. I will be there and look forward to seeing and talking with each and every one of you. The light wine and appetizers after the meeting have nothing to do with it!
Annual Spring Conference: Alaska Botanical Garden's 10th annual conference is titled "Thyme for Gardening." It's a whole day of garden talks, demonstrations and sales on March 19. This always fills up. Go and get your tickets now at alaskabg.org.
Seed racks are in: Nasturtium seeds and canary bird vines always run out.
Nurseries are open: Start visiting and getting seed and seed starting supplies.