Taking divisions from your own (or your neighbor’s) perennials is the easiest way to add to your perennial garden. Divisions guarantee what you’ll get; however, your choices are necessarily limited to what is available (usually plants that spread quickly and are quite common). Commercial seeds will also provide a known quantity, but if you’re willing to trust to serendipity, many pleasant surprises can develop by starting perennials from seeds you have collected.
For greatest success in starting perennials, create a small raised bed in an area protected from drying winds and too much direct sun. Use the frame of the raised bed to support some shading material to protect seedlings. Perennials will grow and thrive in loose soil that holds moisture without becoming waterlogged. A sandy loam to which organic matter such as peat moss or compost has been added is ideal. A small amount of dehydrated manure will provide all the nutrients that the seedlings will require until they are potted or set out in the perennial garden.
Many perennial seeds need to be exposed to cold temperatures for a certain period of time—a process known as stratification or after-ripening—before they will germinate. With seeds sown in the late fall, this happens naturally over the winter. If seeds are to be planted in the spring (or if they are held over from the previous season), first mix them with moistened peat moss and store in a plastic bag in the refrigerator for three to six weeks.
Just before sowing seeds in spring, soak them overnight in warm water to expedite the germination process. Press small seeds firmly into the soil, and plant larger seeds at a depth 2 to 3 times their thickness. Water regularly, and once the plants have developed three or four sets of leaves, thin the bed by pulling out all but the healthiest plants. Most of the seedlings will benefit from a season in the nursery.
These plants tend to be poor dividers and are therefore good candidates for starting from seed: poppies, cardinal flower, foxglove, baby’s breath, monkshood, gas plant, lupine, geum, and mallow.
Certain plants are not recommended for starting from seed: astilbe, lily-of-the valley, mayflower (trailing arbutus), daylily, anemone, trumpet flower, sweet lavender, germander, and spiderwort.