Winter Review: Hardiness Zones

Winter is the ideal dream time for cold-climate gardeners, but it’s also a perfect time to review good gardening practices and increase your gardening knowledge. For this Winter Review we’ll examine plant hardiness zones.

Plant hardiness zones depict general temperature-range regions. To help avoid gardening disappointments, it’s good to know your specific plant zone. Find the USDA plant hardiness zone/s in your state,  then get a closer look by searching by zip code.

If you live in Connecticut, you should not assume a plant growing in one part of the state or region will work in a more northern or southern landscape in the state. On the USDA map, Connecticut ranges through 1 1/2 zones -from 7a in Long Island Sound coastal areas to 5b in the northwest corner.

USDA Plant Hardiness ct_ri zones

The same search at Plant Maps shows Connecticut zones ranging from 7a along the shoreline to 5a in the northwest corner. On both maps the ‘a’ designates a slightly warmer and the ‘b’ indicates a slightly colder sub-zone within the same numbered zone.

A closer examination of your specific town, may show you living and gardening on the edge. For instance, the town in which I live, garden, and work is divided into zones 6b and 6a on the UDSA map and into zones 6a, 6b, and 5b on Plant Maps Connecticut map. This means a plant that is borderline hardy in my zone 6b garden may struggle in an open, unprotected section of a garden just a few miles to the north.

You could let these designations make your head spin, but don’t. Plant hardiness zones serve as a good general guide when choosing plants most likely to survive in a region, but choosing a plant appropriate for your zone does not guarantee survival.

OLYMPUS DIGITAL CAMERA This tag for Hakonechloa macra ‘Aureola’ informs this Golden Japanese Forest Grass is most likely to thrive in zones 4 to 8 provided it is also planted in soil, light, and moisture conditions that meet its needs.

When shopping for plants at a garden center, in a catalog, or online it is important to pay attention hardiness zone recommendations. Just because one ornamental grass is hardy to your zone does not guarantee all others are. The same is true for many types of shrubs and perennials – not all varieties are equally hardy in the same zones.

If you crave a perennial hardy only to a warmer zone, say a zone 9 plant when you garden in zone 6, accept that this plant is not likely to survive your zone 6 winter. In plant talk this is a tender perennial. If you must have it then plant it knowing it will die over the winter or find out if it can be overwintered in a pot in an unheated garage or basement.

On the other hand, if you crave a perennial hardy to zone 7, but garden in zone 6, the plant might survive when situated in an area protected from harsh winter winds, if given extra layers of mulch, or if planted near hardscape that tends to help maintain slightly warmer soil temperatures.

Taking such steps is taking advantage of microclimates, which will be the topic of my next Winter Review … stay tuned.

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5 comments for “Winter Review: Hardiness Zones

  1. January 13, 2014 at 5:41 pm

    That was very helpful, too few shoppers look at this kind of information when shopping at the nursery…Well done.

  2. January 14, 2014 at 9:10 am

    I have found the biggest issue for hardiness is winter moisture — that’s what affects my plants the most. As you point out so well, in the right soil and wind conditions a zone 7 plant will survive well n zone 6. And if the soil can stay dry enough in winter (but not too dry) many plants can push the zone limits. Winter wet is the biggest challenge here for all my plants at the zone edges, not just the xeric ones.

    • January 14, 2014 at 9:32 am

      Excellent point, Laurrie. Too much soil moisture often causes the downfall of perennials and shrubs … even those hardy to the planting zone.

  3. January 15, 2014 at 10:53 pm

    I love looking at these maps. My town, too, falls in at least two zones (5a and 5b) — which means that some zone 5 plants will make it and others will not. Because my sandy soil is so well drained, I don’t have to worry much about plants having soggy feet in the winter. I think the biggest difference for me is how much snow cover we get in the winter. Although overnight lows here often go down into the zone 4 range (e.g., -25F last week), this usually only happens when there is a pretty deep snow pack providing some protection/insulation for plants.

    • January 16, 2014 at 12:29 am

      Jean, snow protection is always good for plants in winter. This winter we’ve gone through numerous freeze/thaw cycles and our snow cover has only lasted until the next thaw. I’ve already noticed frost heaving in plants put into the ground last autumn. It’s going to be interesting to see what survives.

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