Penstemons, also called beardtongues, are a large group of North American wildflowers, and most of them handle cold winters well. As a group they cover most of the continental US, but the zone on the plant tag matters more than the name penstemon, because hardiness changes from species to species. And the plants that fail over winter often aren’t killed by cold at all. Soggy soil does more damage than low temperatures.
The Typical Penstemon Zone Range
A USDA hardiness zone is a band on a map based on the coldest average winter night in your area, and lower numbers are colder. Each zone step covers 10°F of winter low, so zone 4 sees lows near -30°F and zone 9 near 20°F. Most penstemons are suited to zones 4 to 9.1Gardenia. Penstemon (Beardtongue) – The Best Plants to Grow Some varieties manage zone 3, and a few go as warm as zone 10.2Gardenia. Penstemon (Beardtongue) – The Best Plants to Grow
To find your zone, look up your ZIP code on the USDA Plant Hardiness Zone Map online. Tags usually show a range like “zones 4-8,” and your zone should sit inside it. The lower number reflects how much winter cold the plant has been shown to take. The upper number reflects where summer heat or mild, wet winters start to cause trouble. Zones say nothing about rainfall or soil, and both matter a lot for penstemons.
The map is built from average coldest temperatures over many years, so one unusually harsh winter can still dip below your zone’s range and hurt a borderline plant. If you sit near a zone boundary, choose plants rated for the colder of the two numbers. A yard sheltered by a south wall or a hilltop can run a little warmer or colder than the map says. If your zone falls right at either end of a tag’s range, treat the plant as a gamble and give it your best drainage and placement.
Warmer is not always safer. Many species come from dry, cold-winter regions and dislike mild, damp winters, so a plant rated to zone 8 may sulk or rot in a humid zone 9 garden. The penstemons that struggle there are usually western or southwestern natives that expect dry summers and cool nights, which a muggy coastal or Gulf garden does not offer. The usual problem there is fungal rot of the crown and leaves during warm, wet weather, not heat by itself. Before buying, check the upper number on the tag and whether the plant comes from a dry or a moist region.
Penstemons For Cold Zones 3 To 5
- Foxglove beardtongue ‘Husker Red’ (Penstemon digitalis): zones 3a to 8b, with maroon leaves and white flowers.3Wisconsin Horticulture. Foxglove Beardtongue, Penstemon digitalis ‘Husker Red’
- ‘Husker Red’ caution: some nurseries list it more cautiously at zones 4 to 8, so in zone 3 give it a sheltered spot.4New Moon Nursery. Penstemon digitalis ‘Husker Red’
- Royal penstemon: zones 3a to 7b for low-water gardens where yearly rain tops 10 inches.5USDA Natural Resources Conservation Service. Royal Penstemon Plant Guide
- Pale beardtongue (Penstemon pallidus): zones 4 to 8, tolerating temperatures well below freezing.6Gardenia. Penstemon pallidus (Pale Beardtongue)
- Desert beardtongue (Penstemon pseudospectabilis): zones 5 to 9 despite its desert origins.7Gardenia. Penstemon pseudospectabilis (Desert Beardtongue)
‘Husker Red’ was bred at the University of Nebraska and released in 1983.8Wisconsin Horticulture. Foxglove Beardtongue, Penstemon digitalis ‘Husker Red’ It was named Perennial Plant of the Year in 1996.9Wisconsin Horticulture. Foxglove Beardtongue, Penstemon digitalis ‘Husker Red’ It is widely sold and a safe first penstemon for northern gardeners. Its maroon foliage gives color before and after the white flowers. It still wants soil that doesn’t stay soggy, so hardiness does not replace drainage.
Choosing among these depends on your zone and rainfall. Royal penstemon is the pick for dry, low-water beds, while ‘Husker Red’ and pale beardtongue are more forgiving where rainfall is higher. Pale beardtongue starts at zone 4, so a zone 3 gardener should choose ‘Husker Red’ or royal penstemon. Desert beardtongue starts at zone 5, so it is not the right choice in zone 3 or 4.
Zone 3 winters can reach -40°F, ten degrees colder than zone 4, so pick plants whose tag starts at 3. A south-facing, well-drained bed can help a borderline plant.
Snow helps too. Early, steady snow insulates dormant perennials from the harshest air temperatures, while bare, windy ground in a cold zone is harsher than a snowy one.
Penstemons For Warm Zones 7 To 10
- Foothill penstemon (Penstemon heterophyllus): zones 7 to 10, growing 3 to 5 feet tall.10Epic Gardening. 21 Beautiful Penstemon Varieties for Your Garden
- Scarlet bugler (Penstemon centranthifolius): zones 8 to 10.11Epic Gardening. 21 Beautiful Penstemon Varieties for Your Garden
- Showy penstemon (Penstemon spectabilis): zones 8 to 10; it comes from southern California and Mexico and handles less cold than most.12Epic Gardening. 21 Beautiful Penstemon Varieties for Your Garden
- Desert beardtongue: survives cold to about 15°F and needs very little water.13Calscape. Desert Penstemon
Pale beardtongue tolerates summer heat and humidity, which is unusual for the group.14Gardenia. Penstemon pallidus (Pale Beardtongue) Desert and western species, though, do best with dry summers and little watering once established.15Gardenia. Penstemon pseudospectabilis (Desert Beardtongue) In the humid Southeast, pick heat- and humidity-tolerant kinds and plant in fast-draining soil. Overwatering a desert species is a common way to kill it, so water deeply while the plant is establishing, then taper off.
Foothill penstemon can reach 3 to 5 feet, so it needs a back-of-the-border spot rather than the front of a small bed. It suits mild, dry-summer climates like California’s. Because its range starts at zone 7, it is one of the more adaptable warm-zone species for gardeners at the cooler edge.
Scarlet bugler and showy penstemon are the tender ones. Both start at zone 8, so a hard freeze in zone 7 or colder can kill them outright, and winter mulch will not reliably save them. In a zone 8 garden, choose a spot with fast drainage and protection from cold wind.
A zone 8 plant may die at its first 0°F night, though it can still be grown as a one-season plant in colder areas. Check the bottom zone number before buying online from western nurseries.
Why Some Penstemons Are More Tender
The low, shrubby penstemons of the Dasanthera group are ideal in zones 5 to 8.16North American Rock Garden Society. What Is the Hardiness Zone for Penstemon They can survive zone 4 if covered with evergreen boughs in winter.17North American Rock Garden Society. What Is the Hardiness Zone for Penstemon Penstemon barrettiae, from the Columbia River area, has thick, succulent leaves and is among the most tender of the group.18North American Rock Garden Society. What Is the Hardiness Zone for Penstemon
A tag can overstate hardiness. Shrubby Dasanthera penstemons come from rocky mountain sites where snow often blankets them, so in a garden without that cover they can be hurt by cold they seem rated to survive. Ratings usually reflect air temperature, but wind and winter sun on exposed leaves can damage a plant before the cold alone would.
Foliage habit plays a part. Some, like pine-leaf penstemon ‘Luminous’, keep green leaves all winter, which leaves them exposed to drying wind and sun. Others die back to the ground and rest below the snow.
Different nurseries can list different ranges for the same plant, because ranges are guides based on growers’ experience, not guarantees. Local garden clubs and extension offices know what survives nearby.
To protect borderline shrubby types, cover them with evergreen boughs after the ground freezes, since boughs shelter against wind and sun while letting air move through. Plant them in sharply drained soil such as a rock garden or raised bed, because wet roots in winter harm them as well.
Winter Wet Kills More Penstemons Than Cold
Penstemons need excellent drainage.19Burpee Seeds & Plants. Learn About Penstemon The crown, the base where stems meet roots, rots in soggy soil, especially in winter.20Burpee Seeds & Plants. Learn About Penstemon So plant in gravelly or sandy soil, on a slope, or in a raised bed. In colder zones, add extra winter protection.21Burpee Seeds & Plants. Learn About Penstemon
Mix in grit or gravel before planting, or build a raised bed. Use a gravel mulch rather than thick bark or leaves at the base, and avoid low spots where meltwater pools.
Winter protection can help or hurt. Evergreen boughs shield plants from wind and wild temperature swings. Heavy wet mulch over the crown can trap moisture and cause rot. Leave old stems until spring so the crown isn’t exposed, and remove covers once hard freezes end.
In spring, the base often gives a clue to whether rot or cold did the damage. Rot leaves a mushy, dark base that pulls away easily. Cold damage usually browns the tips while the base stays firm, and a firm crown often resprouts once the soil warms.
Growing Penstemon In Containers
Roots in a pot sit above ground and get colder than roots in the garden. Some penstemons handle it; ‘Purple Haze’ stayed healthy in pots frozen to 18°F.22Journal of Environmental Horticulture. Controlled Freezing of Twenty-three Container-grown Herbaceous Perennials Still, a tag’s zone range assumes in-ground planting, so a pot rated for zone 5 may need the protection of a zone 6 or 7 garden. In zones below 7, move pots to an unheated garage or sink them into the ground for winter. Freezing is not the only risk, because a pot sitting in cold rain or melting snow can keep the crown soggy.
Use a pot with large drainage holes and a gritty mix, such as cactus mix with extra grit. Larger pots buffer temperature swings better than small ones. Water sparingly in winter while the plant rests.
Pots also let you grow a warm-zone species up north. A tender species like showy penstemon can summer outdoors in a pot, then come into a cool, bright spot before hard frost.
For an unheated garage, move the pot in after the plant goes dormant and the leaves have browned or the first hard frosts have come, since the goal is to keep it cold but not frozen solid. Water only lightly once in a while, enough to keep the mix from drying out completely. Bring it back outdoors in spring once hard freezes have passed, and let it adjust to light and wind gradually.