Under favorable conditions, as the years pass the plant will generate more and more stems, growing slowly larger in the process. This is a boon to the ornamental gardener, since planting once results in more decoration every year. Sometimes, however, a plant that is doing this will need to be divided in order to maintain its health and productivity.
Some woody plants act like perennials in colder climates. A good example of this is the butterfly bush, which can become a very large shrub in warmer climes, but when it encounters colder winters it dies back and has to start over again every year.
A special subset of perennials are plants that form bulbs or tubers, where all the energy for the next year's growth is stored in a large underground organ (the bulb), which is exhausted and then replenished or reformed over the course of each growing cycle. The most familiar examples of these are tulips and daffodils (bulbs), and potatoes (tubers).
A perennial should not be confused with a self-reseeding annual or biennial, since those plants die after one or two years respectively but do not need to be replanted because they regrow from seeds in the garden.
- Wile, Dr. Jay L. Exploring Creation With Biology. Apologia Educational Ministries, Inc. 1998