Gardeners looking for a vigorous climber to cover a wall or trellis in only one season will be delighted with ipomoeas. If you have cool springs, sow seeds indoors. Morning glories don't like their roots disturbed, but in cooler climates you'll need a jump on the season or you won't get flowers until late summer.
Start seeds three to four weeks before the last expected frost date. Soak the seeds in warm water for 24 hours before planting, or carefully file or chip their hard overcoats to encourage germination, then soak them. Put them in peat pots so the transition into the garden won't disturb their roots as much. Seeds will germinate in about a week. If you start them too soon, some of the quick-growing varieties will seek a support to climb on, or start twining around each other. If your seedlings get to this point, insert twigs in their pots (carefully, so as not to damage the roots), and transplant as soon as the weather warms up.
In zones with longer growing seasons and milder temperatures, sow seeds outdoors where they are to flower, after the last frost date. Plant morning glories in average, well-drained soil but make sure they get a full blast of sun (especially I. alba). I have grown the tricolor morning glories in partial sun on a western wall. They took longer to flower, but once they did, it was in profusion.
I. alba likes rich soil, but most of the I. tricolor cultivars prefer soil that is not too rich, otherwise you'll get an abundance of foliage and few flowers. Morning glories aren't water lovers, either, and will do well with average precipitation.
Morning glories are twiners: they reach out, pirouetting in their predetermined, typically clockwise direction, seeking something to grab hold of. (The plants are genetically programmed to grow and unfurl in one direction only—watch your plants, you'll see.) The tendrils are far stronger than they appear. Give them a trellis, a string, a lamp post—anything that will allow them to grow upward. And grow they will, until a frost stops them dead in their tendriling tracks.