5 plants to stabilize your garden slopes from rain erosion

In the aftermath of our recent deluge, the topic of mudslides, erosion, and slope stabilization is on the minds of many. In this part of the world, slopes are everywhere, from Santa Clarita and the Anaheim Hills to San Bernardino and Santa Barbara. 

When it comes to horticultural challenges, you can choose between a technological and a botanical fix, and sometimes you may combine the two. For example, if you want a purely botanical fix to the challenge of mudslides or slope erosion, you will want to plant species that do not require irrigation once they have established themselves. You will choose from succulents, California natives, and species indigenous to those parts of the world with Mediterranean climates like our own — Chile, South Africa, lands surrounding the Mediterranean Sea, and parts of Australia – as well as other drought-tolerant selections from almost anywhere.

If you are seeking a technological fix, you will look to terracing as a permanent solution to erosion control on slopes. Terracing is an ancient technology that is still practiced throughout the world today and is employed on hilly and even mountainous terrain for growing everything from cereal crops to vegetables to fruit trees. If you wish to terrace your slope, you may want to utilize railroad ties in this endeavor. However, it is not advisable to grow edibles on the terraces created from railroad ties, since the ties contain creosote, a preservative that contains toxic chemicals. Should you wish to adorn your slope with ornamentals only and want to terrace with railroad ties, you can find them in eight-foot lengths for $45 each at A & K Railroad Materials (akrailroadmaterials.com) in Mira Loma. Home delivery is also an option.

Tower of Jewels Echium wildpretii (Photo by Joshua Siskin)

Blue witch Solanum umbellliferum (Photo by Joshua Siskin)

California fuchsia Epilobium canum (Photo by Joshua Siskin)

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In Southern California, a combination of horticulture and technology has made it possible to cultivate one of our most precious crops on slopes. I refer to avocado farming. Having personally worked in avocado groves in both Santa Paula and Fallbrook, I can testify to the success of growing avocado trees on slopes. Technology comes into the picture with drip irrigation because sprinkler irrigation on slopes is much less efficient than drip. Since avocado trees are somewhat water-needy, it would be far more costly — in terms of water expense — to utilize sprinklers as opposed to drip technology where growing on slopes is concerned.

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The following are ornamentals that grow rampantly on slopes due to rapid spread through sexual propagation by seed (self-sowing) and/or asexual reproduction (cloning) by means of rhizomes.

1. Matilija poppy (Romneya coulteri): Matilija poppy is a gangly and ungainly California native perennial that is somewhat difficult to establish, but once it gets going, it will rapidly spread. Its stems grow up to eight feet in height and its flowers, which resemble jumbo fried eggs with yellow centers and crepe-white petals, reach nine inches in diameter. No plant is better suited for erosion control than the Matilija poppy with its ropy, rhizomatous roots that grow deep and spread. The more this poppy is watered, the longer it flowers and the faster it grows. However, it can subsist on winter rain alone. Matilija poppies have a mild fragrance and dusty, silver-blue, sharply cut leaves that stand up well in vase arrangements. You can propagate this plant by digging up rhizomes with leaves attached. Plant the rhizomes in one-gallon containers and leave them in the shade until new growth is evident, at which point you can transplant them to your slope.

2. Baja spurge (Euphorbia xanti): This is a fast-growing shrub with thin stems that are covered with white or pink flowers from winter to early spring. In its habitat, it is found growing on slopes where it does a fine job of controlling erosion. It also has fragrant flowers, an atypical trait among euphorbias, but its real gift is its multi-faceted means of propagation. Baja spurge spreads using rhizomes, tubers and corms, and it also self-sows abundantly, which means it will rapidly overwhelm your slope. For cloistered gardens, this is not an advisable selection since it will take over every open spot of ground and then some. Yet, if you have a sunny backslope and want something there you won’t have to worry about but still flowers, this may be the plant for you. It can grow up to 10 feet tall but usually stays lower than that, depending on how much you irrigate. It will tolerate drought quite well but will grow much faster when watered during our long dry season.

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3. Pride of Madeira (Echium candicans) and tower of jewels (Echium wildpretii): These two plants show off unusually long, conical flower wands each spring. While the violet-purple Pride of Madeira inflorescences are impressive at up to two feet long, the pink-to-red floral wands of Tower of Jewels may reach an uncanny seven feet. You can see an exuberant pride of Madeira displayed on the bluff that overlooks the old casino building on Catalina Island. Based on my experience, I believe that Pride of Madeira and Tower of Jewels probably self-sow more readily than any other plant of their stature. Once you plant them, you will have them forever and will be in the enviable position of giving away their progeny to jealous neighbors. They need no water other than winter rain and are hardy down to 22 degrees Fahrenheit. Flowering in their second year of growth, both species look good for around three years after that before flowering is drastically reduced and death ensues. Echium flowers are highly attractive to bees, butterflies, and hummingbirds.

4. Incienso or brittlebush (Encelia farinosa): This is a mounding California native with silver foliage and yellow daisy flowers. Incienso means incense in Spanish and refers to its resinous sap that was used for this purpose in the early Spanish missions of the Southwest. Its foliage is also potently fragrant. The brittlebush epithet refers to its stems that are easily broken. Its species name of farinosa is attributable to the mealy (farina = meal or flour) texture of its foliage due to the presence of matted hairs. Sun-reflecting, silver, and hirsute foliage is characteristic of drought-tolerant plants and this one is at the top of that list. It may be short-lived but as long as soil drains well, seeds should easily self-sow and new plants should always be coming along. 

5. California fuchsia (Epilobium canum): This opportunistic California native species, also known as hummingbird trumpet for its attractiveness to the eponymous flutterer, may be seen popping up on canyon hillsides — for example, along Coldwater Canyon and Laurel Canyon boulevards, running north and south between Ventura Boulevard and Mulholland Drive.  California fuchsia spreads by both seed and rhizomes and will naturalize over your hillside as long as soil drains well. Foliage is greenish gray to bluish gray and flowers are orange to red in color. In recent years, densely flowering, compact and vividly colored cultivars have been selected and may be found at nurseries that feature California natives.

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California native of the week: Ten years ago, in a residential neighborhood in Reseda, I encountered the most confounding botanical vista I had ever seen. It left me wondering: Was this an act of man or of God? 

Picture an empty lot at least 5,000 square feet in size covered with thousands of blooming plants of the same species. Never had I seen more perfect plants, not a single blemish on any of them. Even more remarkable, it was late July and the soil was bone dry as if no one had watered the heavily flowering specimens in many months, if ever. 

Upon investigation, I learned that the plant in question was a California native woody perennial known as blue witch (Solanum umbelliferum). I discovered that It blooms nearly all the time, can grow in any type of soil, requires a bare minimum of water, and forms a dazzling three-foot diameter mass at maturity. Its flowers are violet-purple with distinctive yellow centers and the foliage is silver-green. All parts are poisonous and it is recommended for yards visited by deer, who devour nearly every kind of plant but leave blue witch alone due to its toxicity. Although I cannot find a source for this plant or its seeds, four of its floriferous cousins (species of the same genus) are available at the Tree of Life Nursery (californianativeplants.com) in San Juan Capistrano. 

Do you have a species to recommend for planting on slopes? If so, you are invited to share your experience by writing to me at joshua@perfectplants.com. Your questions and comments, as well as gardening problems and gardening tips, are always welcome.

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