What USDA Zone Changes Mean for MN Gardeners

With the warming climate reflected in the 2023 USDA Plant Hardiness Zone Map, a majority of Minnesota gardeners suddenly find themselves in Zone 5, a warmer zone that only a sliver of Minnesotans used to enjoy.

Minnesota USDA Zone Map 2012 vs 2023 comparison

What Has Changed?

The USDA Plant Hardiness Zone Map reflects the previous 30 years of temperatures. The new map, which was released last year, is based on temps from 1991 – 2020, and with Minnesota winters becoming milder, there has been a substantial expansion of Zone 5.

In 2012 when the last map was released, only a tiny portion of very southern Minnesota was in Zone 5a. Now we have a much larger chunk of southern MN in Zone 5a along with most of the Twin Cities metropolitan area, including much of Hennepin, Dakota, Anoka, Ramsey and Washington counties.

With over 60% of Minnesota’s population in the Twin Cities metro area, this update suddenly transforms the majority of Minnesota gardeners into Zone 5a gardeners.

What is the USDA Zone Map?

The USDA Hardiness Zone Map measures the average coldest winter temperatures in each area of the country, and groups them into numbered zones. These zones can be divided into half-zones, denoted by “a” or “b” after the zone number. This has become the standard by which gardeners determine which plants are likely to survive the winter in their area.

Minnesota’s current winters give us growing zones from 3a to 5a, with the following range of average lowest winter temperatures:

  • Zone 3a: -35F to -40F
  • Zone 3b: -30F to -35F
  • Zone 4a: -25F to -30F
  • Zone 4b: -20F to -25F
  • Zone 5a: -15F to -20F

What Can I Grow That I Couldn’t Grow Before?

It’s worth stressing that the USDA zones reflect historical data. So if you had a plant that couldn’t survive the winter five or ten years ago, it still likely won’t survive today. However, if you avoided planting something because it was listed as a Zone 5 plant, it may be worth giving it a shot.

Munstead lavender

Here are some plants you might consider trying:

  • Lavender: This Mediterranean herb whose flowers have both a color and scent named for them is very drought tolerant and deer-resistant. Munstead type lavenders are a safe bet in Zone 5 as long as you give it lots of sun and well-draining soil. Lavender does not do well in wet soil.
  • Butterfly Bush: A small (in MN) bush with showy flowers that are beloved by butterflies. Butterfly Bush is sometimes mistakenly thought of as invasive because in some warmer states it can be. While not native, it is not invasive in MN and even our milder winters tend to keep this woody shrub much smaller than it could be in the south, often dying back over the winter to regrow in spring.
  • Culinary Blackberry: While Minnesota has native species of blackberry — Rubus allegheniensis being the most common — these brambles produce small berries with a milder flavor. The culinary varieties produce larger, sweeter berries and are often thornless, but are generally limited to zones 6 or 5 at the coldest. New Zone 5 gardeners with a protected site might be very happy to try one of the hardier culinary blackberry varieties, such as the Prime-Ark® varieties developed by the University of Arkansas.
  • Sweet Cherry: Sour cherries with smaller, tart fruit for baking have long been grown in Minnesota, but the fresh-eating sweet cherries require at least Zone 5 and may now be within reach of MN gardeners with room and some patience. Remember you’ll need multiple sweet cherry trees to get fruit, and because they can bloom early, there’s a danger that an early warmup followed by a frost could kill the flowers — and with them the years’ harvest — so you shouldn’t expect a harvest every year. (This is the same issue we have with peach trees: their flowers rarely survive our springs. Despite the overall warming trend of MN winters, climate change is making MN springs more volatile).
  • Saffron Crocus: The expensive culinary spice saffron is actually the stigma of the saffron crocus flower. This fall-blooming crocus can survive in well-drained Zone 5 gardens. It’s planted in the fall and first blooms a couple months later, then goes dormant for the winter and summer. The corms multiply each year.

There’s More to Growing Than USDA Zone

It’s important to stress that just because you live in a Zone 5a area doesn’t mean that every plant listed as Zone 5 will grow for you — and indeed it doesn’t mean that you can’t grow a plant from a warmer zone!

Your microclimate plays an important role: this includes everything from soil conditions to sun exposure to wind protection to the vicinity of rocks or structures. Many of the Zone 5 plants listed above have been grown by Zone 4 Minnesota gardeners for years, for example. It’s also true that we can get one abnormally cold winter that could kill off plants that can manage the average winter extremes.

– Written by Brian Wood, Master Gardener