What Does Plant Hardiness Mean?

Read any plant labels or gardening books and you’ll hear the word “hardy” thrown around frequently in reference to plants. But, what is hardiness, and what does it mean to you as a gardener?

A basic definition of hardiness is a plant’s ability to withstand cold winter temperatures. The U.S. Department of Agriculture’s plant hardiness zone map breaks geographical regions into zones based on the average low winter temperatures. These zones give gardeners a starting point when determining what plants will fare well in their gardens.

For example, a gardener living in Colorado, which is zone 5, can be reasonably assured that any plant labeled as hardy for zone 5 or colder will survive a Colorado winter. However, the zone map doesn’t take into account variances due to altitude, humidity or wind, which can also have a bearing on a plant’s ability to survive.

Zone maps and plant hardiness charts have their limitations, but they provide some good, basic information. Look at plant labels and select plants that are hardy in your zone area. You’ll find hardy perennials and annuals to beautify even the coldest, most rugged terrain.

Hardy Annuals

All annuals die each year, so the word “hardy” may seem like a misnomer, but some annuals are more rugged than others. Pansies, for example, are the darlings of the fall and spring garden because they tolerate light frosts. Petunias, impatiens and fuchsias, on the other hand, are finicky, heat-loving plants that wither and die with the first hint of frost. If you live in an area prone to late spring and early fall frosts, try a few of these hardy annuals to keep your gardens bright:

• Pansy
• Poppy
• Sweet pea
• Snapdragon
• Bachelors button
• Black-eyed Susan

Hardy Perennials

Many perennials are hardy to at least zone 4, meaning they survive harsh winters to come back year after year. These plants are often low-maintenance in other regards, as well, tolerating drought, heat and neglect during the summer. Hardy perennials include:

• Daylilies
• Yarrow
• Sage
• Catmint
• Peony
• Iris
• Cranesbill
• Coneflower
• Coral bells

Winter Protection for Plants

A plant that is only marginally hardy in your region may survive with a bit of extra care. Mulch plants with 2 to 3 inches of wood chips or bark in the fall to provide a layer of insulation. Leave dead plant debris in place over the winter to provide insulation, as well.

Another option is to dig up plants, such as geraniums and fuchsias, and overwinter them in a sunny corner of the house. They won’t bloom as profusely indoors, but they’ll survive until the following spring.

Understanding hardiness zone maps is only one piece of the equation to successfully choosing and growing plants. Talk with a nursery specialist about the growing conditions in your garden, including soil type, moisture and sunlight. Tall trees may shelter your yard and reduce wind, allowing you to grow a greater variety of plants successfully.

Want to learn more about plant hardiness?

Check out these resources:
Plant Hardiness from University of Vermont
USDA Plant Hardiness Zone Map by The United States National Arboretum