As you go to the garden center and are looking to buy some plants, keep their life cycles in mind.

If you want something that you don't have to plant each year, don't buy annuals.

Here are tips that will help you buy the kind of plants that you want for your flower garden.

Plants are classified by the number of growing seasons required to complete their life cycle. Generally, these groups are annuals, biennials and perennials.

Annuals will provide continuous blooms throughout the growing season.

Biennials provide blooms during their second year of growth.

Perennials will bloom for two to eight weeks or longer. Bloom time will vary and can occur during the beginning, middle, or end of the growing season.

Annuals take a single year to complete a full life cycle. Most are planted in the spring, bloom in the summer, and die in the fall. A few, known as winter annuals, germinate in the later summer and autumn, are dormant during the winter, and grow during the next spring and summer.

Many plants treated as annuals in northern climates, such as Pennsylvania, are actually perennials when grown in southern climates. These plants are not cold-hardy and are not able to withstand winter temperatures in our hardiness zone.

Except for those that reseed themselves, annuals will not grow a second year unless they are replanted. Annuals are frequently grouped as "hardy," "half-hardy," or "tender." This refers to when seed can be sown outdoors in the spring and their capability to tolerate early spring and fall frosts and winter temperatures.

Hardy annuals include plants such as pansies, ornamental kale, and dusty miller. These plants are able to withstand cold soil and hard frosts, may be winter-hardy, are able to survive winter temperatures if sown in the fall (depending on the severity of the winter) and are ideal for cool weather gardens although they often will die in the heat of summer.

Half-hardy annuals include plants such as snapdragon, petunia and alyssum. These plants can withstand a limited amount of cold temperatures and light frost. However, if the seed is sown too early and germinates, even a light frost may damage the seedlings. Summer heat may cause half-hardy annuals to decline, but cooler fall temperatures seem to revive the plants, often inducing growth and blooming.

Tender annuals include plants such as vinca and zinnia, which cannot withstand freezing temperatures. They should be sown outdoors only after the danger of frost has passed (which is usually May 10 in the Lehigh Valley). The seeds are often sown in a greenhouse during the spring and grown to small plants that are transplanted in the garden after the last frost. Tender annuals will grow fairly well and bloom throughout the heat of the summer.

Biennials take twice as long to complete a full life cycle as annuals. They require a dormant period, induced by cold temperatures, between plant growth and blooming.

Biennials are usually sown in the spring, vegetative during the summer, dormant that fall, live in this inactive state through the winter, flower the second summer, set seed, and die during the following fall. If biennials are grown in regions where winter temperatures are colder than the plants hardiness, a cold frame can be used as a temporary shelter for plants.

Some biennials can be treated as annuals by sowing seed in the summer that will germinate and be exposed to chilling temperatures to induce flowering in the fall and over winter, and resume growth and flower the next spring.

Perennials used in Pennsylvania landscapes are cold-hardy enough to survive winter temperatures, hence they live longer than both annuals and biennials. Perennials are classified as either herbaceous or woody.

Characteristics of herbaceous perennials include top growth that completely dies back to the ground during the winter. Roots and crowns remain alive. Plants send up new growth the following spring; and they usually live for at least two years.

Herbaceous perennials that are not cold hardy, or cannot tolerate really cold climates, usually die when the soil freezes. These perennials are often treated as annuals.

Bulbous plants are often referred to as bulbs, tubers, corms or rhizomes. True bulbs are actually fleshy food storage centers for underground stems from which the next season's plants will grow. Corms are also food storage centers, but are more scaly and solid. Rhizomes and tubers are actually thick underground stems. To be classified correctly, this group belongs with perennial flowers because bulbous plants come back and flower year after year.

Characteristics of woody perennials include that their top growth does not die back in the fall (deciduous plants drop leaves, but stems do not die) and will have larger plants each year as new growth grows from existing stems.

For answers to your garden questions, call the Lehigh County Cooperative Extension Office, 610-391-9840, or Northampton County Cooperative Extension Office, 610-746-1970, and ask to speak with a Master Gardener. Volunteers staff phone lines several days a week, Monday - Friday.

Growing Green is contributed by Lehigh County Cooperative Extension Office Staff and Master Gardeners.