Yes, perennial plants do come back every year, making them a foundational component of a stable garden landscape. A perennial is defined as any plant that lives for more than two years, contrasting with annuals, which complete their life cycle in a single growing season, and biennials, which require two years. This reliable return is achieved through a biological process that allows them to survive periods of cold or drought.
The Mechanics of Perennial Survival
The ability of a perennial to return each spring is rooted in dormancy, a state of reduced metabolic activity triggered by environmental cues. As daylight hours shorten and temperatures drop, plant hormones signal the perennial to cease above-ground growth and begin cold acclimation. This transition involves moving resources from the foliage down to underground structures, such as roots, rhizomes, or the crown of the plant.
Carbohydrates, specifically sugars and starches, are stored in these protected underground parts to provide energy through the winter. This stored energy fuels the new growth spurt once spring arrives. The crown, where the stem meets the roots, and the root system house the dormant buds that will produce new shoots. Plant cells also produce compounds like sugars and salts that act as a natural antifreeze, protecting them from cold damage.
Identifying Dormancy Versus Plant Death
Gardeners often mistake a dormant plant for a dead one, especially when the above-ground foliage has died back. Since the timing of emergence varies greatly among species, patience is necessary to avoid prematurely removing slow-to-wake plants. Some plants require a specific duration of cold temperatures, known as chilling hours, before their buds are ready to break dormancy.
For perennials with woody stems, such as shrubs, the scratch test is a reliable method to check for viability. Gently scratch the outer bark of a small stem to reveal the tissue underneath. If the tissue is bright green and moist, the stem is alive; if it is brown, brittle, or dry, that section has died. For herbaceous perennials that die completely back, check the crown for firmness; a firm crown indicates life, while a mushy one suggests rot or death.
Preparing Perennials for a Successful Return
Gardeners can take several proactive steps in the fall to ensure a perennial’s successful return. While some herbaceous perennials should be cut back to reduce the risk of pests and diseases, many, like coneflower and ornamental grasses, are best left standing. Leaving the dried stems and seed heads provides protection for the crown and root system, and the seed heads offer food for birds.
Applying a layer of organic mulch, such as shredded bark or straw, helps insulate the roots and regulate soil temperature. Mulch is particularly helpful in preventing frost heaving, which occurs when freeze-thaw cycles push the plant’s crown and roots out of the soil. This exposes them to damaging cold and drying winds. Mulch should be applied after the ground has begun to freeze, but kept a few inches away from the plant’s crown to prevent rot.
A final, deep watering before the ground freezes is important, especially in regions with little late-fall rainfall. Well-hydrated plants are more resilient against the harsh, drying effects of winter wind and frozen soil, a condition known as winter desiccation. For newly planted or tender perennials, adding a protective layer of pine boughs or substantial mulch provides extra insulation for successful survival.