USDA Hardiness Zones


quoted with kind permission from

Henry Fieldseth


I wrote this little article for last year's plant sale catalog because we get a lot of questions about winter hardiness. And we sell a lot of plants rated zone 5 or 6, but that we know will do well here.
Henry Fieldseth, Minneapolis, Minnesota, USA, zone 4      May 2012

Why You Don’t See Zone Numbers in Our Catalog

Those colorful bands across the map called USDA hardiness zones are based exclusively on minimum temperatures. The maps put us in USDA hardiness zone 4, with minimum temperatures in the –20F to –30F range. And it does, indeed, get that cold here.

A plant’s survival, however, is dependent on many factors, including soil, sunlight, watering, drainage, exposure to wind, mulch, snow cover, and of course the winters’ minimum temperatures. Note that minimum temperature is just one of many factors. Those zone numbers over simplify the game. Within our “zone 4” gardens, there are many microclimates that allow plants to survive. The “heat zone” around the foundation of a heated home is just one example. The wind shelter from buildings and fences can make a huge difference in a plant’s ability to survive our long dry winters. For other plants, shelter from late winter sun
will keep the buds alive through the brutal freeze-thaw cycles of our often tentative springs.

When long-time gardeners compare notes on perennials, it usually turns out that one has never been able to get a certain plant to survive the winter, while for another the same plant grows like a weed. The zone numbers listed for plants in books and online are good guidelines, but they can be confusing and often too conservative. The experience of other gardeners in your area is a much better guideline. So:
• Talk to your neighbors. Join a garden club. Ask questions and share your own experience.
• Ask at the Master Gardener booth if you have questions about the proper soil, light and watering for the plants you have chosen. They can also tell you if your perennials need special winter protection.
• Give us feedback. We want to hear how the plants do in your garden. That's how we will all find out what plants are successful here.
Here is a list of those we will be selling next weekend at the Friends School Plant Sale in Saint Paul, Minnesota, USA. We expect all of these to do well in our climate. We are also selling the native wild flower, /Aquilegia canadensis/, in the native plants section.
/Aquilegia ecalarata/ has survived winters well in pots left above ground. Not many plants can handle that here.

The ***** means local garden writers have rated these as excellent for "cold climate gardens." The entire catalog is online at the URL below, both as a searchable database and as a PDF.

Columbine Aquilegia

$1.50—2.5” pot:
P118 Alpine Blue, A. alpina —Low-growing with large, deep
blue flowers midsummer. From central Europe. 18”h
P119 Biedermeier Mix, A. hybrida —Semi-dwarf, bushy classic
columbine in bright colors. ***** 12”h
P120 Black Barlow, A. vulgaris plena —Fully double, spurless,
purple black flowers above fern-like mid-green leaves. 28”h
P121 Blue Star, A. caerulea —Large blue flowers with long
spurs. U.S. native. 24”h
P122 Nana Alba, A. flabellata —Pure white flowers. ***** 8”h
P123 Nora Barlow, A. vulgaris plena —Double pom-pom, spurless
flowers in pale green and pink. 24–30”h
P124 Songbird Goldfinch —Lemon yellow. ***** 30”h
P125 Songbird Mix —***** 24–30”h
$2.00—2.5” pot:
P126 Music Red and Gold —Lots of large red and gold long
spurred flowers. Rich colors. Blooms all spring and early
summer. ***** 18”h
$3.00—3.5” pot:
P127 Clementine Blue, A. vulgaris —Double blues. Blue-green
foliage is attractive all season. Excellent as cut flowers.
P128 Clementine Red, A. vulgaris —Upward-facing double
spurless fuchsia-red flowers. Blue-green foliage is attractive
all season. Excellent as cut flowers. 18–24”h
$6.00—4.5” pot:
P129 Clementine Salmon Rose, A. vulgaris—Spectacular double
blossoms, aging from rosy salmon to lavender. Blue-green
foliage is attractive all season. Excellent as cut flowers.
P130 Columbine, Dwarf Aquilegia ecalarata
Adorable columbine blooms in dark purple; dainty, airy foliage.
Small enough for troughs. Also known as Semiaquilegia. 15”h
$6.00—4.5” pot

Henry Fieldseth


From Carrie, here's the link for USDA zones  and further comments about zones from that site. Here is the definitive temperatures for each USDA zone, and out of interest I'd suggest Swansea, South Wales, UK is a wet version of zone 8 or 9  

USA is part of a big continent, unlike the islands of Britain where we are surrounded by ocean that evens out summer and winter temperature differences....and brings in a lot more rain than ever reaches inner large continental areas of similar temperatures. And Swansea is on the western side of Great Britain...catching much of the precipitation from the wet air driven over vast areas of ocean by the dominantly westerly winds.







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