JW: It's always rather exciting when we have that feeling of being “in the zone,” when everything is going just right. But when we are working with plants or gardening, it's important to be in the zone--the USDA Plant Hardiness Zone-- and for the first time since 2012, that map has been updated. I'm Judy Wagley, and this is “From the Ground Up!” Monica Jean is Michigan State University Extension Field Crop Educator. Thanks for joining me today.
MJ: Thanks for having me.
JW: Monica, what is a USDA plant hardiness zone?
MJ: Physically speaking, it is a map that you can pull off the USDA website and look at it. But like how you can apply, it would be when you go and purchase your seeds, let's say you go to the local store and you look at the back. It will have a plant hardiness zone listed. Those numbers are pretty important and they correlate right to this map. So what you're doing is you're taking that, let's say it says it's a 5A type of plant, and you come back and you look at this map. 5A is a version of a bluish color--and then you would look at the map and you would see, “Is that over the area that I live in?” And if it's not, then you really need to consider whether you should be planting it or not.
JW: So the plant hardiness zone map is kind of the standard by which gardeners and growers determine which plants will thrive in that particular location?
MJ: Yeah. And so when you're looking at this map, there is a scale of color that goes across it, giving you an idea of what is acceptable. And it is at 10° average annual extreme minimum temperature increments, and that's how those zones are established. So if you look at that and you have a seed you have found that does well in temperatures even colder than where you live, that plant could still do very well in your area. It's if you are in a colder place and you come across a plant or some seed that only does well in the zone that is warmer, right? You're planting something that performs in warmer weather and that's where you would say, “No, this probably is not going to be successful, so let's not kill a plant!”
JW: Yes. I believe there are 13 zones, and zone 1 is way north. In Central and Northern Michigan, we are around what-- 4 or 4A? 5 or 5A?
MJ: Yeah, we actually don't even have too many 4A. So 4A is that -30 to -25. We see that more up in like Gogebic or the Northern West side of the UP. We are definitely more like if you want to call Isabella kind of the point that divides it, that's where it goes from the -10 to -5 as the minimum temperature and this, by the way, it's a 30-year average from 1991 to 2020.
JW: Yeah, and this map hasn't been updated since 2012, so this is new and hot off the presses.
MJ: And that 2012 map would have actually been established from a 30-year period-- even prior to that. So this is quite new in relationship to the last publication and the 30-year average it was using.
JW: And this map is important for anyone who's going to grow any kind of plants, the home gardener or farmers or whatever. So they know what will grow in their area like you said.
MJ: Yeah, a lot of times when the farmers purchase seed, this has been done for them. They don't necessarily even have to look at the map. The maps may be used in order to test like a cold germination on the plant and in order to give that recommendation from that seed dealer to the farmer, saying “This would work well for your area.” They've looked at that map for the farmer, but I still encourage them to take a look, especially if they are considering a new crop. Maybe they went to a field day or a farm show further south of here. And they see something different and new. I get those calls sometimes around cover crops. “I saw this cover crop and it looked great!” Well—it is--except. we may not be warm enough for. That is usually the problem.
JW: So for someone who has just moved to Northern Michigan from, say, Texas, those same plants are not going to grow here.
MJ: No, no!
JW: What are some of the differences in this new map?
MJ: In general, it's more mild, meaning that our area is not as cold on average as it used to. USDA outlined several different factors that could be causing that. Now, there still are areas-- like if you get up to Crawford County or Gaylord—that looks pretty much the same. Hasn't really changed too much.
JW: Bottom line, I guess Monica, is when it comes to plants in your yard and garden or on your farm, it's really great to stay in the zone! Monica Jean is Michigan State University Extension Field Crop Educator. Thanks for joining me today and for all of this valuable information.
MJ: Ohh yeah, thanks for having me.
