Bedding plants that go into the garden in spring are generally warm season or summer annuals. They should perform through summer until the weather gets too cool for them the following autumn. Bedding plants that go into the garden in autumn are generally cool season or winter annuals. They should perform through winter until the weather gets too warm for them late the following spring.
That sounds simple enough. Each type of bedding plant performs best within a specified season. Since they are annuals, they complete their life cycles within a single season within a single year. Of course, it is not so simple here where seasons are as unique as they are. Winter is mild. Summer is arid. Some bedding plants that are annuals in harsher climates may survive as perennials.
For example, busy Lizzie and wax begonia are warm season annuals in most climates. They succumb to frost as weather cools in autumn. Locally, they can survive through winter if sheltered from mild frost. Any that survived through last winter can regenerate now. As bedding plants, they will not be as uniform as they were last year. However, their variability would be fine for mixed bedding.
If sheltered and warm enough, wax begonias may actually continue to perform right through winter. If they dislike the aridity of summer, they can even perform slightly better through winter than they do through summer. Their best performance is often about now and again in autumn, between the two extremes of summer and winter. They challenge their designation as a warm season annual.
Even some of the bedding plants that really are annuals may not behave as such. Alyssum and nasturtium can disperse seed to replace themselves before they finish. They are not true to type, so their progeny eventually revert. Nonetheless, simple yellow and orange nasturtium and white alyssum are splendid for many relaxed gardens. Nasturtium might perform better in summer or winter.
Bedding plants usually know more about what they should be doing than those who are managing and manipulating them.
Highlight: Trailing lobelia
No other bedding plants exhibit such rich blue as trailing lobelia, Lobelia erinus. Cultivars with white, purplish pink, purple or sky blue bloom are still not quite as popular as the favorite cobalt blue bloom. Individual flowers are tiny but very profuse and uniform. Some have white centers. The narrow leaves are tiny as well, and finely textured. Some cultivars have dark purplish bronzed foliage.
Individual plants are only about three to six inches high and wide. Cultivars that are more rounded and densely foliated are excellent for edging. They are very popularly planted in single rows, and alternating with alyssum. Trailing types exhibit wispier growth that stays a bit lower and spreads a bit wider. They do not trail far, but cascades nicely from urns and hanging pots of mixed annuals.
Although grown as a warm season annual, trailing lobelia can survive as a short term perennial where winters are mild. Fresh new growth develops out of the centers of overwintered plants about now. If pressed gently into the soil just before they are replaced by new growth, scraggly outer stems can develop roots. They just might grow into new plants before the originals eventually die off.