Yearly plants germinate, flower and set seed in one growing season. They often provide repeated flushes of bloom and color, supplementing perennials and shrubs that may bloom only once a year. Self-seeding annuals provide gardeners the very best of two horticultural worlds, combining the advantages of annuals along with the simplicity of perennials, which return every growing season without the gardener’s intervention. The very best self-seeding annuals are those that produce lots of viable seedlings, but not so many that they dominate the landscape or become incredibly invasive.
One of the very best of this medium to tall self-seeding annuals is that the easy-to-grow giant larkspur (Consolida ajacis). This delphinium relative produces distinctive white, pink, blue or blue-purple blooms on stems that climb around 4 feet tall under great conditions. The plants require sunny websites and well-drained soil to produce abundant flowers and self seed freely. Another medium to tall self-seeder is cosmos (Cosmos bipinnatus), featuring daisy-like red, white or pink blooms on 1- to 4-foot stems. During the flowering season, picking or deadheading stimulates flower production. Cosmos have been reported as invasive in a couple of places.
Low, ground-covering moss rose (Portulaca grandiflora) is not a rose in any respect, but an annual prostrate plant with thin, succulent leaves. Every rose-form flower lasts just a day, but the plants self seed readily. Suitable for containers or garden beds, moss rose blooms in just about every shade except for true blue. Nasturtiums (Tropaeolum group) are exceptional low-growing self-seeders. Blooming in shades of cream, yellow, red, orange and bi-colored combinations, nasturtiums thrive in thin soil and can withstand drought as soon as they are established. Both leaves and flowers are also edible. Climbing types are also available.
Common morning glory (Ipomoea purpurea) is a climbing vine that is also an superb self-seeder. Reaching 6 to 10 feet tall, with heart-shaped leaves, morning glories grow rapidly and produce scores of viable seeds. The species form of the annual is purple, but cultivated varieties can be found in many shades of blue, purple, purple and bi-colored combinations. The associated moonflower (Ipomoea alba) bears similar white, trumpet-shaped blooms and self seeds readily. The fragrant blooms are borne on twining stems that climb 10 to 12 feet. Moonflowers have been reported as invasive in a couple of places.
Reducing spent flowerheads or deadheading prevents plants from setting seed. To support self-reliant, gardeners should refrain from deadheading plants at the end of this growing season. Mulching, which helps conserve soil moisture and prevent weeds, can also avoid self-sown seeds from germinating. Utilizing landscape material between plants additionally prevents germination. Because of this, gardeners who wish to support self seeding will probably need to weed, either by hand or using a hoe. Hand weeding also allows gardeners to remove unwanted plants; either weeds or even excess seedlings of desirable annuals.