The following tropicals are true annuals that you can either grow from seed or purchase inexpensively as cuttings in the spring. Let them freeze in the fall, then start anew in the spring, or overwinter indoors in full sun for even bigger plants the following year.
The huge, bean-like seeds of the fast-growing castor bean plant (Ricinus communis) should be started indoors, in peat pots, about four to six weeks before the last frost. The big, star-shaped leaves can be green or reddish. The insignificant flowers produce attractive, spiky seed capsules (the seeds are poisonous, so keep well away from children and pets). Overwintering isn't necessary; young plants have larger, more exotic leaves than mature ones.
The newest cultivars of coleus (Solenostemon scutellarioides, syn. Coleus blumei) are more compact, with leaves in a variety of shapes and colours—pinks, reds, yellows, purples, oranges—but insignificant blooms. Pinch off flower stalks; the plant tends to collapse after blooming. Normally thought of as a shade plant, dark-leafed coleus, especially, also thrives in sun. Bring in cuttings; coleus is easy to grow indoors.
Other “annuals” (i.e. plants to be treated as annuals) include copperleaf hibiscus (Hibiscus acetosella ‘Coppertone' syn. ‘Red Shield'), iresine (Iresine herbstii), ornamental sweet potato (purple, golden and variegated cultivars of Ipomoea batatas), Swedish ivy (Plectranthus spp.), Pseuderanthemum spp. and purple heart (Tradescantia pallida ‘Purple Heart', syn. Setcreasea purpurea).
Easy to please
Summer care of tropicals is a snap. Unless it's unusually hot and dry, just douse them thoroughly once a week. They're heavy feeders, though; apply a slow-release houseplant or container fertilizer at the beginning of the season and a soluble fertilizer each time you water. Full sun isn't absolutely necessary; the long days of our northern summers mean that even in partial shade, plants collect plenty of solar energy.
When fall arrives, cut off all food and water to the summer bulbs; cut them back when they die down. The bulbs can be stored indoors for the winter, in their pots, at room temperature or somewhat cooler. Cold rooms are a bit too chilly, even for dormant tropicals.
After the first cool evenings of August or early September, hose down the plants and spray with insecticidal soap before bringing them indoors. They will need lots of sun: place in your brightest windows, keep slightly moist and don't feed again until spring. If the air is dry use a humidifier, or leaves will quickly dry out or be attacked by spider mites. If necessary, give your tropicals a weekly shower to knock off the spider mites before any damage is done—or spray weekly with insecticidal soap.
Tropical exuberance, minimal care: what are you waiting for?