Plants that lose their leaves during the winter are deciduous, while plants that retain leaves are called perennials. Most evergreens will eventually lose their leftovers, but not all in the same season or at the same time. This is the case for most pine trees which typically shed needles that are three to five years old.
Annuals are those plants that complete their life cycle (seed to seed) in one growing season. Most garden plants are annuals. Perennials are plants that grow year after year, often taking many years to mature.
When a subtropical perennial plant, such as a tomato or coleus, is grown in cooler regions, it cannot survive a cold winter and dies. Under these conditions, a perennial plant is forced to grow as an annual.
A biennial plant normally completes its life cycle in two growing seasons. During the first year the foliage grows above the ground while storing food reserves in the root or stem. Many times the wintering form of the plant is called a rosette, which is a group of low-growing leaves around a short stem. During the second growing season, the biennial uses its reserves to bloom. After the first growing season, the cold winter provides the plant with a necessary trigger mechanism for this plant to run amok or send out a seed stalk in the second season. Celery and parsnip are examples of biennials. Many weeds and vegetables are biennial. Although dandelions form rosettes during the winter, they are perennial, living for several years.
Unlike annuals and biennials, perennials don’t necessarily die after flowering. The century plant is one of the exceptions. Combinations of all three categories occur. Asparagus, rhubarb, and many bulb crops are examples of herbaceous perennials in which the aerial parts die each year, yet the roots remain alive to provide new shoots each spring. Boysenberries, raspberries, and other cane fruits have perennial root systems with biennial shoots.
