Below is a list of what are, in my humble opinion, the seven wonders of the Los Angeles plant world, as well as some honorable mentions.1. I initially thought of making such a list many years ago when I first set eyes on what is, in my opinion, the most breathtaking tree in Los Angeles. It is located in the Mildred Mathias Botanical Garden at UCLA. The garden is to be found in the southeast corner of the campus, where it is bordered by Hilgard Avenue along its eastern edge and by Le Conte Avenue to the south. The garden is open 7 days a week from 8 a.m. to 5 p.m. except for Saturday and Sunday, when it closes at 4 p.m. Admission is free.The tree in question is a Torrey pine (Pinus torreyana) and its presence in Los Angeles is highly unusual. You almost never see a Torrey pine in this city, although it is touted as being tolerant of smog. Native stands of Torrey pines are found in only two places: the coastal bluffs flanking Soledad Valley in San Diego County and Santa Rosa Island (one of the Channel Islands).Standing beneath this tree, which appears to have reached its mature height of around 70 feet, you are overcome with feelings of reverence and gratitude. You feel reverence towards the Creator of such a miraculous work of arboreal art. You feel gratitude to the prescient gardener who, decades ago, planted an unassuming seedling that somehow grew into this awe-inspiring pine.While visiting the Mildred Mathias Garden, you may as well take note of some other exceptional trees that are growing there. There is a dawn redwood which is thought to be the tallest specimen of its kind in North America. It was only in 1944, in a remote part of south central China, that the first living dawn redwoods were discovered, a species known beforehand exclusively from fossils. That region of China is the sole habitat of this tree, which is also the only deciduous redwood species. The tree in the Mildred Mathias Garden was planted in 1948.You should also take note of two gigantic rose gums (Eucalyptus grandis), which are the largest representatives of this species in the US, a humongous floss silk tree (Chorisia speciosa) with its green and thorny trunk, and a kaleidoscopic Mindanao gum (Eucalyptus deglupta), just outside the garden entrance, with its glorious rainbow colored, exfoliating bark.2. The oldest tree in Los Angeles, to the best of my knowledge, is a coast live oak (Quercus agrifolia) at Orcutt Ranch in West Hills, which is thought to be more than 700 years old. Of all the botanical treasures mentioned here, it is the only one that, in all likelihood, germinated on its own and grew up without human assistance. This tree imparts to Los Angeles, with its aura of newly begotten riches and transient fame, an aspect of solidity and permanence that feels strange, yet comforting nevertheless. While at Orcutt, you can enjoy a stroll through the old orange grove from which you are allowed to pick fruit, for a nominal fee, at selected times of the year. You can even get married here for a most reasonable sum. The ranch, located at 23600 Roscoe Blvd., is open seven days a week from dawn to dusk and admission is free.3. Entering the king palm forest in the Virginia Robinson Gardens for the first time can be a disorienting experience. At first, you might think that this is just a very sophisticated movie set, that all these trees cannot actually be real. Especially since you are in Beverly Hills. Surely some big Hollywood producer has simply set up this surreal forest for amusement purposes. But then you look closely and realize that these are authentic king palms (Archontophoenix cunninghamii) after all. You learn that this is reputed to be the largest grove of king palms, which are native to tropical Australia, in North America and the only naturalizing collection of such trees. In botanical jargon, where trees are concerned, to naturalize means to drop seeds that produce viable seedlings in place. Virginia Robinson Gardens is open to the public by appointment. You can arrange for a tour by calling 310-550-2065, or by email firstname.lastname@example.org. If you haven’t grinned lately from ear to ear, and have begun to wonder what that sensation might have been like, you need only visit he poinsettia hedge just south of the Ventura Freeway in Camarillo. Take the Camarillo Springs Road exit to get there. This is another one of those cases where you just have to step up to the plants and touch them to make sure they’re real. First of all, who ever saw a poinsettia that was eight feet tall? And a 1,000 foot long hedge of them?When you get done smiling, you just might start to dance. You will definitely want to sprint from one end of the hedge to the other, just to test your endurance against that of this botanical marvel. I wonder if in Mexico, the poinsettia’s native land, poinsettia hedges are as commonplace as those ever blooming oleander hedges once were in California — before a bacteria and its glassy winged sharpshooter insect vector destroyed them.It would be interesting to clone one of these Camarillo poinsettias and see how much cold it could tolerate. I once saw a poinsettia growing outdoors in Granada Hills that was around six feet tall. It was thriving in front of a stucco wall that faced east. If you have a frost sensitive plant but just have to try growing it outdoors, I suggest planting it against an east facing wall. Being in front of a wall means that it will benefit from heat radiating out at night, the same heat that the wall absorbed from the sun during the day. Also, facing east means that if the cells of a plant are slightly frozen, the morning sun will perhaps be enough to quickly thaw them out and keep the plant alive.[As long as we are on the topic of colorful hedges, Arabian lilac needs to be discussed. Its botanical name is Vitex trifolia ‘Purpurea’ which, as you might imagine, references its purple aspect. In the case of Arabian lilac, we are talking about the leaf undersides which, when looking out over a long hedge of this plant, may as well be the top face of the leaf itself, since the dominant color observed is an unmistakably purple or violet hue. Once established, Arabic lilac is highly drought tolerant. There is a sharp pepper scent to its crushed leaves and mildly fragrant lavender flowers are produced.Licorice plant (Helichrysum petiolare) has grey foliage and may be grown, in the manner of Arabian lilac, as an informal hedge. While Arabian lilac can reach a height of ten feet or more, licorice plant stays low, at around three feet tall. Its leaves, when dry or on hot days, emit a licorice scent. Although its flowers are insignificant, it is also drought tolerant once established. Foliage has a pleasantly soft and woolly texture.]5. The Huntington Desert Garden in San Marino is not only unique to Southern California. It is considered by some to be the most outstanding garden of its kind in the world. There are not enough superlatives in the dictionary to describe the treasures found here. The garden consists of 2,000 cactus and succulent species, while the Desert Conservatory or greenhouse, at the garden’s upper end, is home to an additional 3,000. Take note that while the garden may be visited every day of the week (except when closed on Tuesday) from 10 a.m. to 5 p.m., the conservatory is open on Saturdays only, from 10:30 a.m. – 4:30 p.m. You can visit the gardens at no charge on the first Thursday of each month but, in order to do so, you must order tickets in advance, online, through the website at huntington.org.Henry Huntington was in the railroad business and this made it possible for him to develop 10 acres into the desert garden that bears his name. Huntington had an extension to his railroad built right up to his property! This made it possible for him to bring in vast quantities of special soil and rock that a desert garden foundation requires. It was the early years of the twentieth century. At that time, there were no restrictions on digging up plants wherever you found them and so, in 1908, three railroad cars full of plants plucked from the Arizona desert were sent directly to Huntington’s new garden site.There are two principle take home lessons from the Huntington Desert garden. The first is that clustering or massing together many individuals of the same species is a sure way of creating a pleasurable and memorable garden experience. The second is that a sloping terrain makes an important contribution to the excellent soil and air drainage that are essential for growing desert plants. Cactuses and succulents abhor standing water around their roots and therefore demand fast draining soil, enhanced by sloping topography. Many of these plants are also sensitive to cold and since cold air, like water, rolls downhill, planting them on a slope will diminish the possibility of suffering serious dieback in a frost.6. The azalea maze in the Getty Center garden in Brentwood is a quintessential horticultural extravaganza. Otto von Bismarck, the powerful diplomatic deal maker of 19th century Europe, is famously quoted as saying that politics is “the art of the possible.” Horticulture in its ultimate expression, by contrast, could be defined as the art of the impossible or, to be precise, the seemingly impossible. For instance, growing oranges in Alaska, you might think, would be impossible. However, as long as you have a heated, well-lit greenhouse, you will have no problem growing oranges anywhere, even in the Arctic Circle.Growing azaleas in Los Angeles, while perhaps not as outrageous as growing oranges in Alaska, is definitely going against the grain. The evergreen azaleas in Los Angeles gardens are hybrids produced from species indigenous to East Asia, a part of the world whose wet climate and acidic soil conditions offer a sharp contrast to the dry Mediterranean climate and alkaline soil found in Southern California. The origins of the azaleas that are found in local nurseries and decorate our gardens can be traced primarily to Japan and, to a lesser extent, to southeast China, Korea, the Philippines, and Taiwan. Locally, azaleas are not noted for their longevity yet there are individual specimens in Japan that are several hundred years old and a few of them have trunks that measure more than one foot in diameter. Thus, if you could create the perfect growing conditions for azaleas, whether in your backyard or in containers on your patio, they could conceivably become family heirlooms.The key to growing azaleas is soil conditioning. Some people excavate a considerable volume of soil and replace it with pure peat moss, whose acidity matches the pH of the native Asian soil in which azaleas grow. Others mix sand or top soil until it comprises up to 50% of a soil mix whose other ingredient is peat moss. Maintaining a layer of humus or aged compost around azaleas at all times is also a wise practice which will curb, if not eliminate, the need for fertilization. Under such conditions, water only when soil under the mulch is dry at a two inch depth. Pruning of azaleas is not required except for training purposes or for keeping them at a desired height.7. The transition from the Getty azalea maze to the Descanso Garden camellia forest in La Canada is rather smooth since azalea and camellia share the same East Asian habitat and have similar growing requirements. In 1874, there was a fire on the future site of the Descanso camellia forest. As a result of that fire, acorns germinated and slowly grew into the coast live oak canopy of 1200 trees under which the camellia forest was planted — mostly in the 1930’s and 40’s, but upgraded ever since.Talk about ultimate and extreme horticulture! Here you have a grove of native oaks that, even in a drought, seldom if ever require irrigation, and yet they are underplanted with camellias that demand, according to the Sunset Western Garden Book, “moderate to regular water.” And this is no ordinary camellia collection, either, but the largest in the world, numbering 654 varieties and 12,000 plants Perhaps it’s the soil acidifying effect of the ever present oak leaf mulch that makes this all possible.The Japanese camellia (Camellia japonica) bloom period is arriving now and it will peak over the next two months or so. When March arrives, make sure to visit Descanso’s impressive lilac collection, too, and, a month later, enjoy the first bloom of the several thousand roses in the International Rosarium. Descanso Gardens is open every day of the year, except Christmas, from 9 a.m. to 5 p.m.I would like to publicize other local plant wonders so if you have any to share, please let me know about them. Sending along a photo or two of the plant wonder(s) in question would be greatly appreciated.Tip of the Week For plant wonder honorable mentions, I would draw your attention to the jacarandas on Stansbury Avenue a couple of blocks south of Ventura Boulevard in Sherman Oaks, to the sycamore trees on Cantura Street, one block south of Ventura in Studio City, and to the sequoia trees adjacent to the Franklin Canyon Reservoir north of Beverly Hill. (Take an extra moment to make full stops at Franklin Canyon stop signs, which are camera equipped. Not making a full stop will generate a $175 ticket.)Last but not least, I would be remiss not to include the Theodore Payne Foundation native plant nursery, a horticultural wonder beyond compare, in this discussion. Nowhere will you find such an immaculate display of unblemished and vibrant containerized plants. Significantly, there is a placard next to each species describing its growth habit and cultural requirements in great detail. There is no other local nursery that approaches this one, whether as an aesthetic or as a learning experience. It is located at 10459 Tuxford Street in Sun Valley and is open Tuesday to Saturday from 8:30 a.m. to 4:30 p.m.