Hardiness Ratings: You have probably seen zone ratings in plant descriptions. What do these mean, and how can they help you plan?

To help gardeners choose plants, various systems for rating hardiness have been developed. A plant is considered hardy in a region if it can grow and thrive there without requiring special protective measures such as insulating with straw mulch.

The USDA Hardiness Zone Map divides the country into regions based on the average minimum winter temperature. Always check the hardiness rating of a plant you are considering, and compare it to the zone you’re in. If you live in USDA Zone 5 (minimum winter temperature -20 F), choose plants that are rated to Zone 5 or lower. If you choose plants rated to Zone 6 (-10 F) or higher, you may lose plants to freezing injury.

You may be able to grow plants rated to one zone warmer than yours if you live in a particularly warm spot, such as near a large body of water, or if you place the plants in a sheltered spot where they’re protected from strong winds. However, if you are just starting out with perennials, why take the chance? Choose plants that are reliably hardy.

Alcea rosea
‘Single Mix’

Hollyhocks are a prized cottage garden plant that can grow to 6 to 8 feet tall. They are widely adapted growing in USDA zones 3 to 9.
‘Butterfly Blue’

Long bloom season and beaudtiful color made this plant the Perennial of the Year in 2000. Hardy in USDA zones 3 through 9.
‘May Night’

This salvia from Germany features rich indigo colored flowers that reach to 20 inches tall. It’s hardy in USDA zones 4 to 9.

‘Magnus’ is an improved echinacea variety that has large daisy-like rose-pink blooms measuring up to 7 inches across. It holds its petals aloft, instead of allowing them to droop.

Feathery red blossoms brighten up moist, shady spots in late spring and early summer. Flower spikes make lovely cut flowers.

Sun or Shade: After hardiness, sunlight is your most important consideration. Choose plants that are adapted to the light levels in your garden. Don’t plant sun lovers under dense trees, and don’t plant shade lovers where they’ll be exposed to blazing mid-day sun. Plant descriptions give the light preferences for plants, so take these to heart. You may be able to grow a sun lover in partial shade, but you may get fewer flowers or weaker growth. Place it in a spot where it can really shine!

Planning for Continuous Bloom: Most perennial plants have a distinct bloom period, lasting anywhere from a week to a month or more. Plant descriptions usually include an approximate bloom time, such as "early summer" or "autumn." A few will describe certain plants as continuous bloomers, but even these usually have a period of peak bloom. When planning your garden, consider bloom times carefully. If you mistakenly choose all early summer bloomers, you may be disappointed when there’s only foliage in your garden from midsummer on.

Perennial plants take some time to get established. You may get a few flowers in the first season, depending on the size of the plant you’ve purchased, but you’ll need to wait a season or two for the real show to begin. Plan to add some annual flowers to your new perennial beds to carry you through the first growing season.

Credit: National Gardening Association