Understanding Plant Life Cycles Can Be Tricky

One of the most daunting things about garden design is understanding how, and for how long, plants will likely thrive and reproduce (or not) in your yard.  The gardening terms can seem confusing or vague:  annual, perennial, self-sowing, hardy, tender, etc.  But understanding these terms can go a long way in helping you develop a landscaping plan that succeeds.

Zinnia

Zinnia

To start, the terms annual, biennial and perennial refer to a plant’s natural life cycle, and to a lesser degree, how reliably it will appear year after year in your garden.

Annuals complete their life cycle in one year or growing season.  They sprout, leaf out, flower, set seed; and then the entire plant, down to the roots, dies.  The only thing that ensures the plant’s continuance from one generation to the next is the seed it drops after flowering.  Examples of popular annuals include poppies, zinnias, marigolds and most vegetables.

purple-foxglove-299412814486288VhN

Foxglove

Biennials have a two-year life cycle, in which they develop foliage the first year and produce flowers the next, then set seed and die (or die back to a bulb). These plants typically require a cold dormant period after the first year in order to develop flowers the second.  Common examples include foxglove, pansies, hollyhocks and vegetables such as cabbage.

Perennials are plants that live for more than two years.  The aboveground plant may die back to the ground in its dormant season (typically winter), but it reemerges from its root system or bulb the following year.  Peonies, coneflowers, yarrow and bleeding heart are examples of popular perennials.  While a perennial reemerges and spreads from the original plant from its root system, it might also set seed and create a new, separate plant.  Certain Black-Eyed Susan varieties do this.

Peony

Peony

What can be confusing for home gardeners is that the above definitions often only apply when the plant is given its natural or ideal growing conditions.  True perennials in mild winter or tropical climates might not survive the first winter in, say, the Sierra foothills.  For example, perennials such as geranium, lantana and impatiens should be thought of as annuals here, as they will likely be killed by the first hard frost. Put those same plants in a more tropical climate, and they do in fact behave as perennials, returning the following year.

There are a few other common points of confusion when it comes to the life cycles of garden plants.  First, the term “perennial” does not mean forever.  There are short- and long-lived perennials.  Some, such as columbine and Shasta daisy, typically will live only several years before they start to fade and die, while stalwarts such as peonies, day lilies and lilacs can live for decades.

Morning Glory

Morning Glory

Just because a plant is said to “self-sow” (reproduce itself by dropping seeds), that doesn’t mean you can bank on it creating new plants every year.  Some self-sowers, such as columbine, gloriosa daisy and spider flower, are reliably successful at yielding new plants from seed, but others, such as morning glory and moonflower, with their hard seed coats, can be iffy unless you intervene by soaking and scarring them.  Plus, the conditions under which seeds will actually germinate have to be just right; and even then, birds might eat them before they have a chance to sprout.

The terms “hardy” and “tender,” while not part of a plant’s life cycle per se, are important in this context, especially relating to perennials.  These terms refer to a plant’s ability to withstand cold temperatures.  Those that tolerate some amount of short-term freezing are cool-season or “hardy,” whereas those that are killed or injured by freezing temperatures are warm season or “tender.”  The growing “zone” designations on nursery plant tags and in gardening books are guides to a plant’s winter hardiness by area.

To design a garden that will bring you the most pleasure, consider each plant’s life cycle, lifespan and hardiness for your climate.

Rachel Oppedahl is a UCCE Tuolumne County Master Gardener.  This article first appeared in the Union Democrat.

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