Perennials vs. Annuals: What's the Difference?

Perennials, unlike annuals, are plants that come back every year. However, they are often invisible during their dormancy phase when they die back to the ground before starting regrowth in the spring.

In terms of lifespan, some short-lived perennials are not that different from biennials—plants that complete their life cycle in two years. But most perennials are long-lived, reliably returning year after year for many years if not decades. Choosing perennials suitable for your climate and growing conditions is the most important thing you can do to ensure their health and longevity.

What Is a Perennial?

Perennials are plants that continue to grow for more than two years. They include trees, fruits, some vegetables, and ornamental plants valued for their flowers and/or foliage. Unlike annual plants, perennials return yearly in the spring, provided they grow in a hardiness zone where they survive the winter. The USDA Hardiness Zone assigned to each perennial indicates which temperature range suits the plant. Tender, warm-climate perennials won't tolerate frost whereas for cold-hardy perennials, winters with subzero temperatures are a necessary part of their natural lifecycle.

Perennials vs. Annuals

The lifespan is a key difference between perennials and annuals. Other ways to tell them apart are:

• Perennials bloom for shorter periods than annuals.
• They grow slower than annuals.
• In their early years, they tend to produce fewer blooms and most don't bloom in their first year. Annuals on the other hand stand out by their showy blooms.
• Some perennials, especially in warm climates, are evergreens that keep their leaves year-round and do not die back in the winter.

Benefits of Perennials

No matter what the size of your yard, adding perennials to your plantings has significant benefits:

• Less effort and money: Perennials, unlike annuals, don’t have to be replanted every year. Especially long-lived perennials are an excellent investment in your landscape that pays off year after year. 
• More sustainable: Because perennials grow slower and less vigorous than annuals, they require less watering and fertilizer. Many perennials are drought-tolerant, help with erosion control, and increase biodiversity by providing food and shelter for wildlife, pollinators, and beneficial insects.
• More plant choices: Among the numerous perennials available for each hardiness zone, there are generally plentiful choices for specific growing conditions such as shade, nutrient-poor, dry, or clay soil, soil pH, and urban pollution.

Types of Perennials

Perennials are divided into two main groups: woody and herbaceous perennials. Trees and shrubs are considered woody or non-herbaceous perennials. Herbaceous perennials are plants with soft, green stems; they are flowering or non-flowering. Ornamental grasses fall into the category of herbaceous perennials.

Tropical perennials may enter a period of dormancy during which they don’t grow much. Perennials in colder climates die back to the ground over the winter and regrow from the base the following spring.

Caring for Perennials

Although perennials require different and usually less maintenance than annual plants, they are not entirely carefree. Follow this basic checklist to grow healthy, long-lived perennials,

• Soil: Make sure the soil texture meets the needs of the plant. Most perennials need well-drained soil. If the soil has poor drainage, amend it with compost or other organic matter to add nutrients before planting.
• Mulch: Covering the base around the plants with a 1- to 2-inch layer of organic mulch at least once a year keeps the soil moist and cool in hot weather and insulates the roots in the winter. Mulch also suppresses weeds.
• Monitoring for pests: Check your plants regularly throughout the growing season for pests and diseases because the earlier you detect and treat a problem, the better.
• Deadheading: Encouraging more blooms is not the only reason to remove spent flowers. Deadheading the flower stems of non-repeat bloomers, such as hosta and astilbe, ensures the plant directs its energy to its roots and leaves rather than setting seeds.
• Division: Numerous perennials benefit from being dug up and divided to maintain vigor. Some need division every couple of years and others, such as peonies, virtually never need division unless you want to make more plants.
• Seasonal clean-up: Removing dead stems and foliage of herbaceous perennials helps to prevent perpetuating diseases but cutting plants back does not have to be part of the fall cleanup, it can still be done in the spring before the new growth starts. Many perennials benefit from an additional layer of protection during the winter.

Choosing Perennials for the Garden

Before purchasing perennials, know your hardiness zone and observe the sunlight and shade patterns of the planting area. That way you select perennials that require sun or shade. If you have a problem with deer, look for deer-resistant perennials.

In addition, since perennials bloom for short periods, make sure to include plants with interesting non-blooming foliage. Plant species native to your region are usually best adapted to your climate. Avoid planting species with invasive potential—for most, there are excellent native plant alternatives.

• Flowers: Coneflowers, ice plants, and Shasta daisies are flowering perennials with longer bloom times than the average perennial.
• Shrubs: Azaleas and hydrangeas are flowering perennial shrubs.
• Ferns: All ferns are perennials, some are evergreen, and they usually thrive in locations that are too shady or damp for other plants. Ostrich fern is a very winter-hardy fern.
• Groundcovers: When choosing a perennial groundcover, consider the amount of foot traffic, desired height, growth rate, and whether it should be flowering or non-flowering. For a fragrant groundcover, consider creeping thyme.
• Ornamental grasses: Most ornamental grasses are perennials and come in varied heights. An especially striking native grass is pink muhly grass.