Perennial, Annual or Biennial?

Cheryl Maynard, KC Master Gardener 2003

Perennial and annual are terms that are familiar to gardeners. Sometimes we confront a plant labeled as a biennial. What is a biennial and what do we do with it?

A biennial is a plant with a life cycle that is completed in two years or seasons. It spend it’s first year producing a low-growing rosette of leaves and root system. The plant goes dormant and dies back in the winter. However the following spring, the plant sends up a flower stalk, blooms, and produces seeds.

At the end of the second season, the plant dies, but it has completed its task by blooming and then spreading seeds. Generally, seeds from biennial plants ripen early enough to germinate in late summer. By germinating early, the new seeds complete their first year of growth. Ideally as the two year-old plants are dying off, there’s a new crop of one-year old plants ready to take their place in the spring. Once the cycle gets started, you will have plants blooming every summer. You can choose to purchase your biennial from a greenhouse or nursery when they are already in their second year. The plant will bloom that season and you can avoid growing them from seed.

Once biennials are established, they can be invasive. Deadheading will go a long way to prevent a biennial from taking over your garden. But be sure to leave some seeds for the plant to continue. Young year old plants can be transplanted, but not two-year olds. Once they are in their permanent location, they can be thinned. Biennials can also be grown in containers to help control their spread.

There is no special care required for biennials. They will thrive in well-drained soil with organic matter added regularly. A yearly dose of garden fertilizer or compost is all that’s needed. Add some extra mulch in the winter to protect the year-old plants from extreme cold temperatures.

Here are some examples of biennial flowers. Alcea rosea Hollyhock, Dianthus barbatus Sweet William, Digitalis purpurea Foxglove, Campanula medium Canterbury bells, Lunaria annua Money Plant, Myosotis sylcatica Forget-Me-Not, Oenothera biennis Evening primrose and Viola xwitrockiana Pansy are all biennials.

Many herbs and vegetables that are grown as annuals are biennials. Examples of these are Petroselinum parsley, Daucus carota carrots and Brassica kale. These plants would bloom their second year if they were not harvested.

References:

http://www.organicgardening.com/featureprint/1,7759,sl-5-18-1132,00.html

http://www.dailynewarticles./com/article/861/28860/Biennial_Plants_What_Are_They.html

http://www.echonews.com/1005/gardening.html

http://www.sustland.umn.edu/maint/biennials.htlm