Just the other day at the entrance to a building that benefited from most of the day’s sun, I saw a window box in which an exuberant planting of Profusion zinnias was on display. It was a tomato red variety I had never seen before. I was mesmerized by its fiery brilliance, a fitting tribute to Johann Zinn, born in 1727, from whom the Zinnia plant genus gets its name. At the age of 25, Zinn became director of the botanic garden at the University of Gottingen and at 27 was installed as professor of medicine at the same university.
This combination of professions was nothing new. Until the middle of the 19th century, every kind of sickness was treated with medicinal plants, euphemistically referred to as nature’s pharmaceuticals. Ever since ancient times, physicians have utilized curative plants, plucked fresh from the garden, to heal their patients. Zinn’s brilliance, which featured seminal research in the morphology of the human eye, was tragically cut short when he died of tuberculosis at the age of 31. Yet his legacy was perpetuated for all time when a Mexican wildflower was named Zinnia elegans in his honor.
Profusion zinnias are at the top of the list of summer-to-fall bloomers. You can find them in yellow, orange, apricot, cherry and tomato red, white, and bicolors. They spread with alacrity and, within weeks, a single Profusion zinnia planted from a four-inch container will expand into a dome two feet wide and one foot high.
One of the reasons for Profusion zinnias’ heavy, non-stop bloom is their sterility. If you see a plant that flowers without interruption for months on end, there’s a good chance that it’s sterile. Sterility means there is no seed formation in the flowers that appear. Without the enormous energy input that seed production requires, a plant can focus that energy on pushing out more blooms since, after all, its objective in living is to reproduce, and it will continue to flower in the hope, however vain, that seeds will develop.
Yet this hope is not altogether unfounded since sterile plants, which are invariably hybrids, may sometimes become fertile again. This is achieved through polyploidy, a phenomenon where the chromosomes in a sterile plant’s reproductive organs are spontaneously doubled, an unpredictable and random event, although it may be brought on, however rarely, by environmental stress. Bread wheat is the classic example of this. For 300,000 years, sterile hybrid wild grasses would appear, a tiny number of which experienced chromosome doubling and became fertile. Around 10,000 years ago, one of these polyploid species exhibited the virtues of modern wheat whose seeds, pounded into flour, made bread baking — and the beginnings of human civilization — possible. Other crops that arose through chromosome doubling in sterile hybrids include cotton, tobacco, and certain strawberry species.
Getting back to super bloomers, whether for container or garden growing, here’s a partial list of plants whose sterility explains their explosive flowering capacity:
Erysimum variety Bowles Mauve is a perennial wallflower that grows into a three-foot spherical shrub. When in bloom, it has no rival for flowering effulgence. Wallflowers, to be grown in full or partial sun, include annuals, biennials and perennials, with flowers in yellow, orange, red, mauve or brown. All of them are fertile except for this variety. Sunset Western Garden Book contains a heart-stopping description of Bowle’s Mauve: “Bloom is practically continuous; the plants, though perennial, may bloom themselves to death after several years.” Wallflowers get their name from an imprisoned 14th-century maiden who fell to her death while trying to escape over a wall to meet her lover.
Hemerocallis variety Stella de Oro is a low-growing miniature daylily with rich golden yellow flowers that appear prolifically from May to October, with smaller repeat blooms at other times. The common orange daylily (Hemerocallis fulva) grows on the side of the road throughout much of North America and is seen where roads were built through former homesteads. It spreads effortlessly through underground rhizomes and may become invasive.
African blue basil (Ocimum kilimandscharicum x basilicum) is transformed from a nursery starter plant only a few inches tall into a robust mass of blooms, achieving a four-foot height in a few months. African blue basil grows equally well in sun or light shade. It requires a bare minimum of water and will grace your garden for several years at least, although, like sweet basil, it is easily propagated from cuttings — with shoot ends submerged in a little water in a glass — so that you will have its clones forever. Not as culinarily enticing as sweet basil due to its camphor component, you can still use its leaves to make pesto, to sprinkle over roasted potatoes and to flavor drinks and salads. Flowers are pink with purple tips and attract a legion of pollinating insects.
African basil is also suitable for cut flower arrangements, both in vases and in dry bouquets. This species is an accidental hybrid. One parent is a stout woody shrub that grows more than six feet tall with foliage heavily laced with camphor, while the other parent is Dark Opal, a common garden basil variety with purple foliage. An herbalist was growing these two plants side by side when suddenly a new type of basil began to grow nearby, a hybrid of the other two plants.
Geranium variety Rozanne has violet-blue flowers with a white center that bloom from now until November or beyond. It is extremely hardy and can survive temperatures down to 20 degrees below zero, even if it loses its leaves where winters are cold, remaining evergreen to semi-evergreen in much of Southern California. Keep in mind that what we typically call geraniums are actually their Pelargonium cousins, whether we are talking about common zonal geraniums (the classic red or orange ones in clay pots), or Martha Washington geraniums (with pastel pink, red, or purple flowers and toothed foliage), or ivy geraniums that trail out of containers or along the ground. True Geranium flowers have five petals and are usually pale to royal blue, violet, purple, or pink.
Lavandula x intermedia is the heaviest-blooming lavender. Known as lavandin, it is also the lavender grown most widely for commercial applications because it is larger and thus produces more essential oil than other lavender species. While English lavender (Lavandula angustifolia) has the highest quality essential oil, it lacks the quantity of oil per plant found in Lavandin. Lavindin is the plant you see blooming, row after row, in pictures of Provence, France, taken in mid-July at the peak of lavender flowering. Incidentally, the word lavender is derived from the Latin lavare, meaning “to wash,” due to its being added to bath and laundry water for its cleansing effect.
I was incentivized to write about the flowering capacity of sterile hybrids after observing the behavior of Peruvian lilies (Alstroemeria spp.) in my garden. For years, I had nothing but pink Alstroemeria that spread by self-sowing and rhizomatous, vegetative growth. A few years ago, I was gifted The Third Harmonic Peruvian lily, an orange-flowered, sterile variety. It is a hybrid that grows over four feet tall, dwarfing more common Alstroemeria types. Since it doesn’t form seeds, however, rhizomes of The Third Harmonic are formed in greater numbers than in other Peruvian lilies. This competitive advantage of The Third Harmonic has led to the disappearance of pink Alstroemerias from my garden. The saving grace of this new reality is that while the pink variety stopped blooming in hot weather, the Third Harmonic flowers nearly all the time.
Do you have a story to tell about a long-blooming plant? If so, send it to Joshua@perfectplants.com. Your questions and comments, as well as gardening conundrums and successes, are always welcome.
California native of the week: California marsilea or hairy water clover (Marsilea vestita) has the foliage of a four-leaf clover, even though it is a fern. In the manner of most ferns, Marisela reproduces both by spores and rhizomes, which, in its case, can grow under water. Although at home in ponds, this species will succeed in soil that is kept moist. In spring, its emerging fronds (fern shoots) grow six inches long before unfurling four bright green triangular leaflets per leaf. Hairy water clover is hardy to 10 degrees below zero.