Annuals complete their entire lifespans within a single year.

Perennials survive for more than a single year.

Biennials grow vegetatively during their first year, and then bloom, disperse seed and die during their second year, but that is another story.

Most species that are appreciated as annuals here actually have potential to be perennials, even if only short term perennials. They are only replaced annually because it is easier than maintaining them through their dormant season.

For example, busy Lizzy is a warm season annual that gets installed for spring and replaced with cool season annuals for autumn. However, if cut back and sheltered from frost, it can survive through winter to perform for the following spring and summer. Actually, it can survive perennially like this for quite a few years, and as it ultimately deteriorates, it can replace itself with its own cuttings or layered stems.

Brent did this with New Guinea impatiens from last year. He neglected to replace them for winter (which is quite brief there), and then noticed that they resumed growth as winter ended. Now, they are huge and even more spectacularly florific than they were last summer.

The picture above shows where I camp out in his backyard when I go to Southern California. Most of the white bloom to the right is actually ivy geranium that cascades below the New Guinea impatiens, but most of the white bloom to the left is New Guinea impatiens above ivy geranium. (White on white was not quite as monotonous when each of the two species maintained its distinct form last year.)

This other pair of potted dwarf Alberta spruce surrounded with the same New Guinea impatiens above, with a close up below, flanks the steps to a small terrace at far western margin of the garden.