He had notice d that in our mild Southern California climate many garden plants are self-sowers, plants that drop fertile seeds which germinate to become “volunteers,”little gifts of nature springing up in places where we may or may not want them. For example, many years ago in March or April I brought home from the nursery a 4-inch-size potted plant. It’s bright green, feathery foliage was dotted with neat little daisies with white petals and yellow centers, like a miniature marguerite. “Paludosum daisy (Chrysanthemum paludosum)” said the tag. Having heard it was a good choice for edging beds, I popped the little plant into the ground on the edge of a flowerbed where it quickly expanded to about a foot high and wide, bloomed its head off for six weeks and promptly died. “What a dud!” I thought. This remained my opinion until the following fall, when all over the garden hundreds of little paludosum daisies popped out of the ground. In January they began to bloom and continued flowering through winter into spring. All I had to do was weed them out of areas where I didn’t want them, thin them out where they grew to thickly, and move a few to other places. Thus I was introduced to joys of the self-sowers, those generous plants that sprout from seeds they or the birds sow in your garden year after year. Chrysanthemum paludosum (or Leucanthemum paludosum, as it is now called) is a short-lived, cool-season annual and such an avid self-sower that I have never needed to purchase another.
Self-sowers can be can be native or exotic. They can be annual, biennial, or herbaceous perennial. They may also be woody plants, such as trees, shrubs, and climbers. In mild-winter zones we plant the cool-season annual and perennial flowers in fall so that we can enjoy their flowers all winter into spring, and warm-season annuals and perennials in late spring to enjoy them in summer and fall. But when working with self-sowers the gardener doesn’t need to worry about timing. Each seed will sprout at the right time of year for that particular species in a specific garden depending on where it is. Factors impacting germination include soil temperature, day-length, light, the amount of rainfall or irrigation, and climate zone. Because all these factors vary, seeds that sprout easily in my garden might not be the same ones that sprout in yours. Cerinthe major, for example, won’t germinate in my garden, but a few miles inland it germinates and comes back year after year.
Throughout the Southwest many wildflowers such as Mexican hat (Ratibida) will come back year after year once established. Mexican hat has two methods of self propagation since once planted it is perennial but it also comes up from seeds. I know a patch in a hot dry roadside location outside a garden wall where it was planted over 15 years ago and it still comes up every year.
African scurf-pea (Psoralea pinnata) is a rare, short-lived shrub or small tree with feathery foliage and leaning trunk, blanketed in late spring with small, fragrant, azure-blue to violet, pea-shaped blooms with white wings. Riparian in its native habitat, it’s become a pest in moist parts of Australia. In Southern California it survives occasional drought in gardens, but not in the wild. Provide good drainage and prune hard after bloom. For tree shape, prune to the most upright leader. When plants eventually die, they leave ample progeny and straight branches useful for garden stakes. For knock-out color contrast, plant with azaleas and camellias; they bloom at the same time.
Madeira geranium (Geranium maderense), a biennial or sometimes triennial, is the largest botanical geranium and seldom found in nurseries. This astounding plant has large deeply cut leaves and produces an enormous central inflorescence, three-feet across, composed of hundreds of deep pink, magenta-centered blossoms. Flowering lasts March through April, then the plant dies leaving many seeds that germinate in October. You’ll have plenty to grow and share. Never cut off leaves; their stems bend down to support the plant and store starches that feed the huge inflorescence. If you need to move plants, do so before winter solstice or they won’t bloom. Protect from frost and give each plant a big handful of slow-release 14-14-14 fertilizer prior to a late winter or early-spring rain.
Despite their easy care virtues, garden plants that sow themselves share the ability to survive with many weeds, so it’s wise to grow them in conjunction with a few rules. One wise rule says “Any plant growing where it is not wanted is a weed.” This is particularly true with trees. Torrey pine, Victorian box, Washingtonia palms, Monterey cypress, and floss silk tree (Chorisia speciosa) are just a few of the trees whose seeds self-sow in my mild coastal climate zone. In interior climate zones other trees will germinate, such as deciduous fruit trees. Occasionally, a chance seedling may become a famous variety, such as the Gordon apple, but most are useless. Some self-sown ornamental trees are garden treasures. Seedlings of Japanese maples are worth potting-up as gifts for friends since they often turn out to be far hardier specimens than fancy varieties bought in nurseries. But if gardeners fail to weed out all unwanted trees and shrubs like Pride of Madiera, and climbers like honeysuckle, their gardens will soon become over-shaded jungles.
Some plants are so generous with their seeds that weeding them out where they’re not wanted may be a problem. Among our loveliest perennials, Santa Barbara daisy (Erigeron karvinskianus), butterfly verbena (Verbena bonariensis), and common gaura (Gaura lindheimeri) share the weedy habit of spreading throughout the garden. Others such as annual borage and the biennials, foxglove (Digitalis) and Madeira geranium (Geranium maderense) are easy to pull out or share with friends. Columbine (Aquilegia) usually isn’t perennial in mild zones, but if you leave the ground undisturbed until late winter or early spring you may find a little circle of baby plants right around where the parent grew. Dig them up and plant them where you want them. Other plants sow themselves so avidly and are so tenacious once established that you should think twice about planting them the spectacular orange Peruvian lily (Alstroemeria aurea) and fortnight lily (Dietes iridioides) are like this, spreading both from roots and seeds. Beware the fashionable grasses, some of which plant themselves into wild lands. Pampas grass (Cortaderia selloana) and common fountain grass (Pennisetum setaceum) are well-known pests that have become impossible to eradicate. Now other exotic grasses including eulalia (Miscanthus), fountain grass (Calamagrostis), sea oats (Chasmanthium), and the lovely Natal ruby grass (Rhynchelytrum) are escaping from gardens and spreading into the wild. Some exotic wildflowers, such as crown daisy (Chrysanthemum coranarium), too, have been criticized for invading the wild, but crown daisy is mainly a roadside plant and cannot survive amidst chaparral.
Some self-seeders, such as nasturtium (Tropaeolum), are easy to pull out when they sprout where you don’t want them. The problem with nasturtiums is that compact types revert to climbers. You may plant elegant varieties one year and end up with rank climbers ever after whose large leaves hide the jolly flowers. I have this type, but since the leaves look rather like lily pads and I have reached that happy age when I can garden for my own pleasure and not for what other people think, I don’t mind as much as I used to. My advice is enjoy the self-seeders with gratefulness for their bounty but with an equal measure of caution. If you stay away from the trouble-makers, the others will make your gardening life much easier.
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