Perennial herbs are plants that survive the winter and regrow in the spring, offering a sustained harvest without the need for annual replanting. The ability of a plant to survive cold temperatures is categorized by the United States Department of Agriculture (USDA) Plant Hardiness Zone system, which uses average minimum winter temperatures to map out climate regions. By matching an herb’s cold tolerance to your specific zone, you can select plants that are likely to flourish long-term.
Defining the Zone 5 Climate
USDA Hardiness Zone 5 indicates a climate where the average annual minimum winter temperature falls within a range of -10°F to -20°F, or -23°C to -29°C. This temperature range is the defining factor for whether a perennial plant can successfully survive the dormant winter period. The zone is often further subdivided into 5a (-15°F to -20°F) and 5b (-10°F to -15°F). Selecting herbs rated as hardy to Zone 5 ensures their root systems can withstand these deep freezes.
Hardy Herbs That Return Annually
Several aromatic and culinary herbs are reliably perennial in the challenging Zone 5 climate, ensuring a consistent yield each spring. Chives, a member of the onion family, are one of the earliest to emerge, providing a mild onion flavor from their hollow, green leaves. These cold-tolerant herbs have a clumping habit and require deadheading of their purple flowers to prevent aggressive self-seeding, which spreads them throughout the garden.
The mint family provides numerous hardy options, including peppermint and spearmint, which are vigorous to Zone 5 and below. Due to their tendency to spread aggressively via underground runners, or rhizomes, mints should ideally be planted in containers or areas where their growth can be contained by physical barriers. Oregano, another aromatic member of the mint family, is equally resilient, though its spreading nature also necessitates careful placement or containment.
Woody, Mediterranean herbs also offer cold-hardy varieties suitable for this zone. Common Thyme, with its small leaves and creeping habit, is generally hardy to Zone 5, especially when planted in well-drained soil. Sage (Salvia officinalis) is a shrubby perennial that often retains some of its velvety, silvery-green foliage through the early winter months, with its hardiness extending to Zone 4.
Lavender can also be grown successfully, but specific varieties like ‘Munstead’ or ‘Hidcote’ (English Lavender types) must be chosen, as they possess the necessary cold tolerance for Zone 5 winters. These varieties should be planted in a location that provides protection from winter winds and offers excellent drainage, as their roots are particularly susceptible to rot from excessive moisture during the cold season.
Ensuring Survival Through Winter
Successfully overwintering perennial herbs in Zone 5 requires specific actions in late autumn. Before the ground solidifies, provide a deep watering to ensure roots are hydrated and resist desiccation. Stop active watering once the ground freezes, however, to prevent rot.
The proper application of mulch is a primary defense against winter damage, serving to insulate the soil and maintain a more stable temperature. A layer of organic material, such as straw, shredded leaves, or wood chips, about three to four inches deep, should be placed over the crown of the plant once the ground has frozen solid. This layer prevents the damaging freeze-thaw cycles that can heave plants out of the soil, exposing their roots to the air.
Most perennial herbs benefit from minimal pruning in the late fall, as the remaining stems can trap insulating snow and protect the plant’s crown. The temptation to “clean up” the garden should be avoided, as extensive cutting back can leave the plant vulnerable to winter injury. For woody herbs like sage, pruning should be limited to removing only the most damaged or leggy growth, reserving any major shaping until the following spring.