One thing you do have to consider with perennials, that is irrelevant for annuals, is the hardiness of the plant, and whether your area gets so cold in winter that it will kill your perennial. You should not try to grow plants that will not withstand the temperatures of your area. The map below will give you a good idea of the hardiness zone in which you live and the average minimum temperature you can expect in winter. Of course, zones can vary slightly in either direction depending on local conditions.

Microclimates can also influence the minimum temperatures even in different areas of a garden, so that a particular plant will thrive on a moist, shady spot on the north side of your house, but languish on the hot, sunny south or west side of your house. Cold air runs down and collects at the bottom of a hill where you may need to plant more cold-hardy selections, while a fence or dense hedge can block winds and trap heat, allowing you to grow plants of a higher zone. That being said, perennials are sown the same way as other seed, the only difference being the timing and the weather!

In the north, most perennials are sown outdoors from spring through summer, up to two months before frost, which allows time for the plants to mature before the rigors of winter set in. Others are sown in early spring or later fall because they need cool or freezing temperatures. Whatever the case, you will find the correct information in the Flower section. Handled this way, most perennials will bloom the second year from seed. Some, like Shasta Daisy, Chrysanthemum or Gloriosa Daisy, will bloom the first year from seed if started early enough.

Summer sown perennials may be started in beds or may be germinated in flats indoors or outdoors. Using flats outdoors instead of open beds does give you more control of growing conditions. Simply rest the flats on tables, benches or other racks, but try to avoid the ground, which may invite insects and slugs. Seeds sown in hot summer require heavy shading, lest they dry out. They should be placed on benches or tables in the shade of a tree or under a roof. If a coldframe is used,  cover the sash with burlap or other shading material, and remove the shade gradually as the seeds germinate.

Biennials can be planted much like perennials. Plant the seeds spring or summer and place them in their permanent position in fall for bloom the following spring or summer.