How plants can grow in the least hospitable places


Plants can grow just about anywhere, including on steep embankments and precipitous slopes. I have even seen them growing out of cracks in walls, whether naturally rocky cliffsides or man-made fortresses.

One of my favorite plants for step terrain is rock rose (Cistus spp.) This native of the Mediterranean exudes a dark resin that has been used for incense since ancient times. If rock rose had nothing but its leaves, this would be sufficient recommendation to have it in the garden. It would be in the elite class of other spicy plants that are grown primarily, if not exclusively, for their foliage, including cooking sage (Salvia officinalis), lemon verbena (Aloysia triphylla), cardamom (Elleteria cardamomum) and allspice (Pimenta dioica). All of these spices may be grown in the Valley, although allspice will need protection to survive a cold winter.

The musky resins and volatile oils produced by rock rose and other Mediterranean-climate plants have two purposes. First, they increase sap viscosity and so reduce water loss from leaves during the long dry season. Second, they make it easier for the plants to catch fire, a beneficial event in their life cycle since blazing heat is required to germinate their seeds.

Rock roses, which do not have thorns, are called roses on account of their five-petaled flowers that resemble wild, single-layered rose types such as rugosa roses. They are referred to as rock roses due to their rocky habitat, where they are frequently the only plants to be seen owing to the ability of their tenacious roots to grow under rocks and extract water that collects there.

Up until today, Mediterranean goat herders from Spain to the island of Crete follow the ancient practice of leading their flocks into thickets of rock rose. As the goats feast on the plants, their beards and thighs become saturated with rock rose resin. Special combs are then used to comb out the resin, which is known as labdanum or ladanum. Labdanum has been identified as one of the spices in the cargo hauled by the Ishmaelite caravan that brought Joseph to Egypt. Labdanum has also been labeled as one of the 11 ingredients of the incense mixture used in the Holy Temple in Jerusalem. Rock rose resin has also been used in perfumes and for fumigation. Finally, those beards for which Egyptian pharaoahs were famous were crafted from clumps of goat hair held together with sticky rock rose resin.

Getting back to its flowers, rock rose produces them in abundance. Although each bloom lasts only a day, flowers open continuously for two to three months. Flower colors are white, salmon, magenta or purple. Some species have red, fingernail-shaped markings at their petal bases. In the manner of Mediterranean-climate plants in general, including many California native species, rock roses are highly sensitive to poorly drained soil and overhead irrigation. I have often seen them die suddenly, yet where irrigation is sparingly provided they can last for more than a decade.

I have seen rock roses growing on steep, unirrigated embankments on the north side of the Foothill (210) Freeway as you approach Pasadena, as well as on the east side of the Golden State (5) Freeway as you approach Valencia. Close by on the same waterless slopes, I have also seen the pale orange flowers of native monkey flowers (Mimulus aurantiacus) bloom in profusion.

Fiberglass plant (Wigandia urens) is another species that is undeterred by precipitous terrain. For years, I have marveled each winter at the blooming of this curious species on the east side of Beverly Glen Boulevard, not far from Mulholland Drive. Heart-shaped leaves are over a foot in size and soft purple flowers rise above the foliage on long stalks.

Fiberglass plant gets its name from its prickly trichomes or leaf hairs which, research has shown, become more abundant as summer temperatures rise.

These insulating trichomes keep foliage cool and reduce transpiration or water loss through the leaves.

Dudleya, sometimes referred to as chalk liveforever, is the most outstanding succulent genus of Southern California. It seems to pop out at you on the side of the road from Wrightwood to Thousand Oaks. As long as the natural landscape is undisturbed, and even in some populated areas, dudleyas will find a home. Invariably, it seems, that home is found on the most vertically oriented location for miles around. Simply put, daredevil dudleyas are happiest hanging on the side of a cliff. I don’t know how they get there, but when you first see one nestled in the crevice of a dirt precipice or granite wall, you are caught completely off guard.

Typically shaped as a rosette, with powder blue to white foliage, a dudleya in its habitat has an aura of unreality to it. A dudleya can seldom, if ever, be fully appreciated in a garden where it is usually situated as just one among an often large collection of succulents. These other succulent species may have their own unique characteristics, despite having rather humdrum habitats as compared to that of the dudleya.

From a reader:

I work as a docent in Placerita Canyon and I found it interesting to read in your column that manzanita leaves are good for poison ivy treatment.

Manzanitas are blooming right now on the Los Pinetos trail up Placerita Canyon trail and it looks like snow on the ground where the lantern flowers have dropped. Do you think manzanita would work on poison oak as well, since they tell us we only have poison oak (poison ivy is generally not found west of the Rockies) in Southern California? How would you apply it?

I am always looking for ways to soften the effects on kids when we hike. They seem to love to bounce into it.

– Jim Crowley, Saugus

There is anecdotal evidence that manzanita can be used to treat poison oak. Take leaves from manzanita branch tips and boil them in water. Apply the boiled concoction, still hot, with a cloth to the affected area and let it dry in the open air. Repeat this treatment three times a day for a few days. You can also try a product called mountain mud (, which contains infusions from manzanita and other plants.

Tip of the Week

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