Technically, the word perennial only refers to a plant that lives longer than two years. So a perennial in Zone 7 could be the same as a perennial in Zone 4; however most likely the assortment of viable perennials in each zone is vastly different.
Generally speaking, a plant is classified as a perennial if it can survive to Zone 7. Above that range, plants become tender perennials or annuals.
So for the purpose of this article, we will only consider the "hardiest" of hardy perennials, plants that are hardy to Zones 4 and lower (or higher in latitude). Even if you aren't one of the brave few who garden in Zone 4 or lower, the plants on this list are definitely tough enough to survive your area's worst winters.
Alpine Rock Cress (Arabis alpina)
|Alpine rock cress is a low growing (6 to 12 inches) perennial that blooms light pink to white blooms and grows best in full to partial sun. Hardy to Zone 3, it is one of the first plants to bloom in early Spring even in very cold climates. It is easily propagated by cutting and also by burying shoots in soil to create new roots. Alpine rock cress makes an excellent rock garden plant or a ground cover among spring bulbs.|
Sea Holly (Eryngium planum)
Blue Dogbane (Amsonia tabernaemontana)
Liatris (Liatris spicata)
Dwarf Goldenrod (Solidago sphacelata)
|Dwarf Goldenrod makes an excellent drought tolerant plant and is hardy to Zone 3. This dwarf variety will grow only 2 feet tall and stays generally compact. The blooms look like frothy yellow fingers that reach out from the top of the plant. Dwarf goldenrod will grow best in full to partial sun and somewhat poor soil.|
Creeping Phlox (Phlox subulata)
Bleeding Heart (Dicentra spectabilis)
Veronica (Veronica spicata)
Obedient Plant (Physostegia virginiana)
Ligularia (Ligularia dentata)
Monkshood (Aconitum columbianum)
|Lungwort comes in a variety of cultivars that each has its own interesting foliage pattern. They almost look like someone spilled or splattered bleach on their thick, hairy green leaves. They make an interesting statement in shade and present small blue, purple or pink blooms in mid-Spring. Lungworts are hardy to Zone 4 and require moist soil.|
Basket of Gold (Alyssum saxatilis)
|Basket of gold is a shrubby perennial, hardy to Zone 3. There are many different cultivars which represent different shades of yellow blooms. Basket of gold, also known as gold dust, grows up to a foot high and will blooms continuously from mid spring through early summer. It is an excellent xeric planting and will work well in rock gardens. It needs full sun and dry, well draining soil.|
'May Night' Salvia (Salvia x sylvestris)
|'May Night' salvia is a rewarding perennial, hardy to Zone 4. It blooms violet-blue spikes all summer long if deadheaded. It is a magnet for bees and butterflies throughout the season. It will increase in size every year and can reach up to 3 feet tall. It is one of the first plants up in the spring and will tolerate many different soil types and moisture levels.|
Balloon Flower (Platycodon grandiflorus)
|Balloon flower or bellflower will reward you with lots of blue blooms even with very little care. Balloon flower is very late to emerge in spring but it will be quick to catch up with other perennials. It will thrive with full sun in poor soils and varying levels of moisture. It is hardy to Zone 3. Balloon flowers resent being moved so take care not to disrupt its rootball.|
Grayleaf Geranium (Geranium cinereum)
|There are many beautiful cultivars of Geranium cinereum, such as 'Ballerina' and 'Purple Pillow' (pictured at right). All are hardy to Zone 4 and require full to partial sun with good drainage. Most varieties will stay compact, growing only a foot tall and a foot and a half wide. Another hardy geranium to try out would be Geranium sanguineum, bloody cranesbill, which is hardy to Zone 3.|
You must be weary in higher zones (lower in latitude) though, because plants that are this hardy can do one of two things in your garden: they can flourish so well that they are invasive without having any winter cold to put them in check, or they can overheat in your warmer weather and hot sun so much that they will never survive. Generally speaking, if a plant is hardy to Zone 2, it won't be a good fit for a Zone 9 or above garden. Well, you can't have ALL the good plants down there!
Special thanks to dahlianut for her recommendations for this article!
Plant Files photo credits:
|bmuller - Veronica (thumbnail)||Kennedyh- Monkshood||Toxicodendron- Tiarella|
|Tcfromky-Veronica||Papijo- Lady's Mantle||Wandasflowers- Penstemon "Husker's Red"|
|Crimsontsavo- Yarrow||Redsnowflake- Obedient Plant||Art_n_garden- Sea Holly, Dwarf Goldenrod|
|Dave- Bleeding Heart||Sanannie- Ligularia||Poppysue- Blue Dogbane|
|Grampapa- Creeping Phlox||Sherlock221- Astilbe||Bootandall- Pulmonaria|
|Todd_Boland-Geranium cinereum||Fro_Bro26- Balloon Flower||Goswimming-Lungwort|
|hczone6-Basket of Gold||Daryl -May Night Salvia, Rock Cress, Liatris|