I saw the most stunning mini-waterfall of green spilling out of a planter box the other day and just had to take a closer look to ascertain that this was not a fake plant, so flawless was its needle-like foliage. It turned out to be a prostrate swamp oak (Casuarina glauca var. Cousin It). The origins of this plant are a mystery, and although it has been in cultivation for many years, it has yet to produce flowers or fruit. It grows to a height of less than a foot but may spread as much as eight feet, and can grow in any soil type, from swampy to bone dry. Planted in the ground, it has a mounding growth habit.
This ground cover is a far cry from its arboreal kin, the Casuarina species known collectively as she-oaks, which may grow as tall as 70 feet. They were once used as street trees in Los Angeles for their drought tolerance, columnar growth habit, and attractive silhouette against the sky. However, their aggressive roots eventually invalidated them for this purpose, although they are still used for windbreaks or privacy screens. The genus name Casuarina is derived from cassowary, a Malay word for a flightless tropical bird whose drooping feathers are matched by the drooping foliage of the she oak. The “she” descriptor references a she-ing sound made when the wind whistles through its branches.
Although they are not legumes, Casuarina species also make their own nitrogen with the assistance of nitrogen-fixing bacteria in the soil. In Kenya, Casuarina seedlings are interplanted with crops to provide them with a ready source of nitrate fertilizer. Crops such as sweet potatoes, peppers, peanuts, onions, and watermelon are planted under or around mature Casuarinas so they can benefit from the enriched soil. It happens that our own California lilac (Ceanothus) shrubs fix nitrogen with the same bacteria (Frankia) utilized by Casuarinas. So if you plant vegetables around your Ceanothus, don’t be surprised if they exhibit a lushness of growth hitherto unseen.
It so happens that a number of outstanding ground covers have cousins that are notable trees. There are more than 1,300 Acacia species, with over a thousand of them native to Australia. The vast majority are trees or large shrubs, but Acacia redolens var. Low Boy is a ground cover that grows only 1-2 feet tall and has the characteristic yellow flower spheres that are produced by nearly every Acacia species. Foliage is elliptical and blue-gray in color. Acacia cognata var. Cousin It is a shaggy clump of foliage that grows with little attention and is an intriguing choice to fill a parkway or a container. Its soft look provides a welcoming feeling when located along an entryway or at an entrance proper.
Grevillea is another genus of mostly Australian plants with some memorable ground covers among them. Grevillea thelemanniana var. Baby grows only 10 inches tall and sports bright red flowers on and off throughout the year. Grevillea x gaudichaudii is a prostrate species, also with red flowers, whose foliage is reddish as well. You can find these and other Grevillea ground covers in addition to a host of hundreds of other species from Down Under at Australian Native Plants Nursery (Australianplants.com). It’s located in Casitas Springs near Ojai.
In contrast to most Grevilleas that you find in the nursery trade, silk oak (Grevillea robusta) is a 60-foot-tall, majestic tree with a symmetrical and pyramidal shape when young. It has a stately presence and displays giant orange and yellow flower combs in late winter or early spring. However, this tree should not be grown near a house or other structure because it eventually creates deep shade under which nothing will grow and produces a constant litter of leaves. But if you have a large yard and can plant it out of the way or toward the rear where it will mark a property line. And its large, thin leaves do provide excellent material to us as mulch or in a compost pile.
Silk oak seedlings, which grow readily from seed, are among the most elegant subjects you will find for patio containers. With dark green, ferny foliage that is silvery on the back, they make an exquisite statement when bunched together in a pot. When the seedlings become too large for their pots, and you don’t want to go to the trouble of repotting into larger ones, discard them and plant another batch of seeds whose unmatched beauty will soon be on display once again.
When we think of sequoias, we invariably conjure up the world’s tallest and most unforgettable trees. Yet there is also a sequoia ground cover that grows 1-2 feet tall with a 6-12 inch spread. Its botanical name is Sequoia sempervirens var. Nana Pendula/Prostrata. In 1927, the superintendent of the Cambridge University Botanic Garden in England found a witch’s broom growth — a kind of growth generally stimulated by a pathogen — growing at the base of a redwood tree. He took a piece of it and grafted it onto a redwood seedling, and the result was a prostrate plant. I have known about this plant for years, but have never been able to track one down. To the best of my knowledge, the only nursery currently growing it is California Flora Nursery (calfloranursery.com). This nursery is located in Fulton, near Santa Rosa. Unfortunately, the nursery does not ship, so you would have to drive up north to get it. If anyone knows of a closer source for prostrate Sequoia, please advise.
There is a new native plant nursery in Los Angeles. It’s called Los Nogales (meaning walnut trees, in tribute to the endemic California black walnut) Nursery and is located at 4700 Griffin Avenue. The nursery is open from 9 a.m. – 3 p.m. on Friday, Saturday, and Sunday and closed from Monday to Thursday. You can find details of the exact location and where to park at theodorepayne.org. The nursery is a collaborative effort between the Audubon Center at Debs Park and the Theodore Payne Foundation.
Please send your questions, comments and more to joshua@perfectplants.com.