UNITED STATES—Many popular annual bedding plants have potential to be perennial if they get a chance. Cyclamen commonly perform as a cool season annual, only until replacement with warm season annuals. However, after summer dormancy, their tubers can generate foliage and bloom again for several following winters. Replacement is just easier than maintenance.

Real annuals complete their entire life cycles, from germination to dispersal of seed and finally death, within a single year. Biennials generate vegetative growth through their first year, and then disperse seed and die during their second year. Perennials perform for at least two years, whether or not they get any opportunities to do so within home gardens.

Home garden culture complicates this classification though. Those who enjoy gardening expect perennial plants to reliably perform for many years or indefinitely. Many perennial plants do so with only minimal intervention. Some are self-sustaining and might seem to naturalize. That may be why so many smaller or less vigorous types classify as annuals.

Many perennial plants perform better with some degree of intervention.

Another qualification of perennial plants is that they lack woody stems and roots. In other words, they are herbaceous. Palms and species of Yucca that develop trunks classify as perennial plants also, but for simplicity, the larger types are herbaceous trees. Generally, perennials are terrestrial. A few are epiphytic (live in trees) or lithophytic (live on stones).

Although several perennial plants can survive indefinitely here without intervention, most perform better with some degree of attention. Most ferns are neater if groomed to remove deteriorated fronds. Many grasses benefit from severe shearing during winter. African iris blooms better in response to regular deadheading to remove developing seed capsules.

Perennial plants are very diverse. It is impossible to generalize about their maintenance. One commonality among many is that they multiply. Lily of the Nile can produce so many individual shoots that it can eventually become too congested to bloom. Division of such shoots every several years or so promotes bloom, as well as propagates more plants for elsewhere in the landscape.

Highlight: Lily Of The Nile

The Nile River Valley is a region of extremes. It floods at times, but is hot and dry at other times. Lily of the Nile, Agapanthus orientalis, naturally survives it all. It can easily survive here. However, it survives arid heat by shedding a bit of foliage. Therefore, it is generally healthier here with at least occasional watering through the warmest weather of summer.

The almost spherical floral umbels of lily of the Nile explode into bloom like blue or white fireworks, just in time for Independence Day. They are about six to eight inches wide, on elegantly bare and slightly leaning stalks that stand about four feet tall. Individual flowers are only about an inch or two long. Flowers bloom only once annually, but last for weeks.

With or without bloom, the dense and evergreen foliage of lily of Nile is always lush. The soft and strap shaped leaves are about a foot and a half long, and flare outward from low basal rosettes. New foliage obscures deteriorated old foliage. Fleshy roots firmly secure plump rhizomes. Division relieves crowded rhizomes, and contains their slow migration.

Tony Tomeo can be contacted at tonytomeo.com.