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These lovely ornamental plants are actually on invasive species list

October 5, 2024

If the birth of a child is one of life’s highlights, the sprouting of seeds is gratifying in a similar way. In both cases, you are a partner in the creation of life.

But what will that child or that seedling turn out to be? There is an ongoing controversy whether nature or nurture plays a more prominent role in personality development. In other words, is it the genetic makeup of the child (nature) or the way a child is raised (nurture) that determines their character?

With plants, the answer to this question is simple. Without the proper conditions for growth, a plant will perform below its capacity. For example, a plant that needs a sunny exposure to flower may never bloom if planted in the shade. Or take a plant that needs a cold winter in order to bloom in the spring: If you plant it in a warm winter climate, it could give plenty of vibrant green growth throughout its life, but never flower.

It is especially pleasing to see plants self-sow in your garden since it means you have provided optimum conditions for growth and the nature or genetic potential of the seedling in question can be fully expressed as it develops into a mature plant.

Seeds that sprout on their own might be dispersed from parent specimens you personally planted or from seeds blown in by the wind or deposited by a bird. About a year and a half ago, I saw a seedling of a butterfly bush (Buddleia davidii) begin to grow in my front yard and it has already reached four feet in height. It is located on one side of a pathway, directly across from a mature butterfly bush on the other side, which is obviously its parent. But just when I wanted to gloat about my horticultural prowess in creating the perfect environment for butterfly bushes to flourish, the following thought came to mind: “If a butterfly bush sprouted in my garden without human assistance does that mean that this species could just as easily sprout in lots of other gardens and, for that matter, could it leap the garden fence and make the list of California invasive plants?” Sure enough, it did.

There is a nonprofit organization known as the California Invasive Plant Council (cal-ipc.org) whose mission is “to protect California lands and waters from ecologically damaging invasive plants.” The state of California currently spends $82 million annually in an ongoing effort to control invasive plant proliferation. Invasive plants not only upset ecological balance, but are financially damaging to farmers and ranchers, add fuel to wildfires, displace native plants, and clog waterways. The council has created a list of more than 300 plants used in horticulture — including butterfly bush — than are considered invasive or on the verge of being invasive. These species are pictured on their website in alphabetical order. You will be in for a few surprises — I know I was — when you find some of your favorite plants, including some not so easy to grow, that are listed there

Take Madagascar periwinkle (Catharanthus roseus), popularly known as annual vinca. It’s actually a perennial but is typically grown as a summer annual. Flowers are pinwheels of pink, white, red, or apricot. This bedding plant has a reputation for being finicky since it is highly susceptible to soil fungus and can quickly perish if the soil is not perfectly drained or if overwatered. I have, however, seen it thrive in perennial fashion when watered no more than once a week in sandy soil. The fact that it is invasive is instructive since invasives, by nature, thrive on neglect; otherwise, how would they be so successful in thriving without any human attention?

I was equally surprised to see foxglove (Digitalis purpurea) on this list. It’s one of the more expensive bedding plants but you don’t mind paying more for its opulent display of flowers that resemble fingers on a glove. (Why “fox” came to be associated with this plant’s name is an etymological enigma.) I would never think that pincushion flower (Scabiosa purpurea) would make this list but it does. It’s one of the most charming selections for the flower garden whose multitude of stamens sticking out of a raised central disk really do resemble a pin cushion. Colors range from deep purple and dark red to lavender, pink, and white. A final flower bed favorite on the list is perennial yellow toadflax (Linaria vulgaris), a smaller-flowered version of snapdragon, to which it is related.

A number of my favorite trees are listed as invasive. Fernleaf acacia (Acacia baileyana) is a wonderful small tree with bipinnate blue-grey leaves and fragrant yellow spherical flower puffs. Its form is a shapely dome. Persian lilac or Chinaberry (Melia azederach) possesses two qualities common to trees that tend to make you catch your breath and stand in silent awe: lush, deep green foliage and a perfectly domed canopy. Even in a drought, Chinaberry maintains its fresh and vital look, needing no water other than an average dose of Los Angeles winter rain. It grows rapidly to a height of 30-40 feet.

Victorian box (Pittosporum undulatum) produces a cloud of perfume from its white flowers in the spring and shows off orange fruit containing red seeds in due course. Although typically grown as a specimen tree, it is also utilized for a hedge or as a screen. In the manner of the Chinaberry, its leaves are iridescent, with a rare radiance, especially when observed at a distance. The Mayten tree (Maytenus boaria) is my final arboreal favorite that happens to be invasive. Some people consider it a compact alternative to weeping willow due to its pendant aspect, more narrow form and slower rate of growth than that classic weeping tree. The key to successful cultivation of a mayten tree is to simply let it grow; pruning is an afterthought and may be put off for years as it reaches 20 feet in height only after a decade or more.

As for invasive bulbous or rhizomatous perennials, be aware of African cornflag (Chasmanthe floribunda), yellow flag iris (Iris pseudacorus), bulbil Watsonia (Watsonia meriana), and calla lily (Zantedeschia aethiopica). And before leaving this subject, I have to mention Himalayan blackberry (Rubus armeniacus), whose sweet fruit I have tasted on many occasions. Unfortunately, it crowds out native plants when it jumps over the garden fence.

I must admit to being wistful at the thought of these and many other desirable ornamentals having invasive qualities. If nothing else, this list is instructive in letting us know which plants are probably not as fussy when it comes to their care as we may have previously thought. Invasive plants are highly opportunistic and they don’t need much help from us to thrive.

California native of the week: Engelmann, mesa or Pasadena oak (Quercus engelmannii) is the rarest and most endangered of our native oaks. Although it may grow to 80 feet with a spread of 120 feet, as one specimen in Pasadena has done, it will generally stay under 40 feet in height and is thus a suitable selection for a moderate-sized backyard. There is a breathtaking grove of 250 Engelmann oaks at the Los Angeles County Arboretum in Arcadia. These oaks have an unpredictable growth habit and do not produce a neatly domed or other symmetrical canopy like other oak species. Their blue-or grey-green leaves are distinctive and if you want their acorns to sprout, you do not have to bury them in the ground since they will germinate when left on the soil surface. These acorns were consumed by the local Gabrielino-Tongva tribes living in what would become Los Angeles County. A tribe further south made a sweet chewing gum from pounded and washed Engelmann oak bark. This oak is named for George Engelmann, a German physician who lived in St. Louis but was a botanist of considerable repute who made a tour of the forests of the Pacific West in 1879 when he was 70 years old. You can find Engelmann oaks for sale at the Tree of Life Nursery (californianativeplants.com) in San Juan Capistrano and at the Theodore Payne Nursery (theodorepayne.org) in Sun Valley,

If anyone has experience with an invasive or out-of-control plant that they would like to share, please send it along to [email protected]. Your questions and comments, as well as gardening conundrums and successes are always welcome.

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These lovely ornamental plants are actually on invasive species list

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