Based on my personal experience, I have concluded that a jolly dentist is about as rare as a floriferous gardenia. So it is only fitting that Dr. Cerniglia, the jolliest dentist I know, has a gardenia blooming at full capacity in front of his Reseda office.
Gardenias are recommended for full to partial sun, and this specimen faces south, getting direct sun virtually all day long. Yet, like many plants recommended for full sun, including roses, I have found that gardenias may suffer in such an exposure when summer temperatures soar.
However, I believe this gardenia is thriving in all-day sun due to two factors. First, it benefits from drip irrigation. Drip irrigation is customarily applied daily in summer, keeping soil moist and roots cool, preventing heat stress. Second, this gardenia grows as a foundation plant, meaning that it abuts a wall, a wind-protected location (prevailing winds in the San Fernando Valley come from the northwest) that is invariably beneficial to plant growth. A wall also absorbs heat during the day, which is radiated out to the plants against it at night. Any increase in nighttime temperatures around plants, such as results from radiant heat, especially where tropicals such as gardenia are concerned, enhances growth. It should be noted that, in any case, plants grow more at night than during the day and insufficiently warm nighttime temperatures inhibit the ability of many tropical plants to grow in the greater Los Angeles area.
The gardenia at the dentist’s office is of the Veitchii (VETCH-ee-eye) variety. This is the most widely planted gardenia since it flowers virtually throughout the year. The challenge with gardenias of every variety is to keep their leaves lush and green. Due to the alkaline soil in Southern California, gardenias and other acid-loving plants such as azaleas, blueberry bushes, and coffee trees may exhibit a condition known as interveinal chlorosis; on older leaves, veins are green while spaces in between the veins are yellow. This condition is caused by a lack of foliar iron, even when there is ample iron in the soil. Molecules in the soil with a high pH that contain calcium, such as lime, hold onto molecules of iron and prevent them from being absorbed by plant roots. Iron is an element that plays an important role in the processes of photosynthesis and chlorophyll (plants’ green pigment) formation, and so leaves turn yellow when iron cannot be sufficiently taken up by roots.
Even where soil is at the proper pH (5.0 – 6.5) for growing gardenias, other soil conditions can lead to chlorosis. In compacted or waterlogged soils, oxygen-loving, or aerobic bacteria, are replaced by anaerobic bacteria, which turn nitrate into ammonia. When nitrate – which is the form in which nitrogen is absorbed by roots – is not available, plants cannot form chlorophyll and leaves become yellow. Nitrogen deficiency is the easiest of all botanical mineral deficiencies to diagnose. Nitrogen is highly mobile, and when you see a shoot or a branch with leaves that are pale green to yellow with terminal leaves that are green, you know there is a nitrogen shortage. Meanwhile, since iron does not move well in the plant, its deficiency is first noticed on new growth.
You can acidify your soil by adding peat moss or gypsum to it when planting, by using fertilizer that is formulated specifically for acid-loving plants and by continual applications of compost. The breakdown of compost, in releasing humic acid, has an acidifying effect on the soil. In general, gypsum (calcium sulfate) applied 3 to 4 times a year is a recommended practice since most plants, including California natives, prefer a somewhat acidic soil pH. Manzanita (Arctostaphylos spp.) and California lilac (Ceanothus spp.) — the two classic California native shrubs — prefer a pH between 5-6. Note: A pH of 7 is neutral while each lower number is 10 times more acidic. Thus, a pH of 5 is 100 times more acidic than a pH of 7.
With plants in general, pale green to yellow foliage may not indicate nitrogen deficiency but simply nitrogen imbalance that may be seasonal and self-correcting. Two plants — common hibiscus (Hibiscus rosa-sinensis) and blue potato bush (Lycianthes rantonnetii) — are famous for displaying sickly, yellowish foliage in late winter only to have it change to a lush green, sans fertilizer, as the weather warms. I saw this same phenomenon on my forest gardenia (Gardenia thunbergia) this year. A forest gardenia grows into a columnar shrub up to 10 feet tall or more with symmetrically swirling white blooms. It is not as finicky about soil pH requirements as more common gardenia types. This year, for the first time, its leaves yellowed after flowering at the end of winter, but as summer approached, its foliage turned deep, shiny green again.
Although gardenias are generally considered problematic in our part of the world, when conditions for growth are to their liking, they flower abundantly without special care. Once, in Valley Glen in the San Fernando Valley, I was introduced to a Mystery gardenia that was 20 years old, had never been fertilized and flowered nonstop for months. It faced east and received morning sun only. I am also familiar with a Veitchii gardenia in Sherman Oaks that is wedged against a fence in a side yard next to a concrete walkway. It is watered once a week, is never fertilized and keeps close company with a billowy, vining star jasmine (Trachelospermum jasminoides). It gets a few hours of sun each morning and is covered with flowers throughout the summer. It would appear that just as in real estate, location (or microclimate, horticulturally speaking) means everything to gardenias.
The history of the gardenia in this country is entwined with the botanical investigations of Alexander Garden. Garden grew up in Aberdeen, Scotland, where he studied medicine and natural history before voyaging to Charleston, South Carolina, where he took up residence in 1752. In addition to his medical practice, Garden became an avid plantsman and sent local specimens he discovered back to Europe. It was during this period that the Swedish botanist Carolus Linnaeus began to give genus and species names, in Latin, to plants and animals, a system that would become known as binomial nomenclature. When Linnaeus received a plant from China with flowers that smelled like jasmine, he named it after Alexander Garden (Gardenia jasminoides) for his work in bringing wider recognition to American flora. Linnaeus sent a sample of the sweet-smelling newly named Gardenia shrub to Garden, who promptly planted it in his garden where, serendipitously, the Carolinas’ semi-tropical climate and acidic soil provided the perfect conditions for the first gardenia ever grown on the American continent.
California native of the week: Desert candle or squaw cabbage (Caulanthus inflatus) is native to the Mojave Desert and has a unique look among California natives. From a base of curvaceous grayish green foliage, thick cylindrical stems grow up to three feet tall, sporting reddish-purple flowers. Desert candle seeds sprout readily and you can purchase 30 of them for 10 dollars at Etsy.com Its fruit is an elongated pod that splits when ripe, dropping seeds that are likely to germinate in place. As for growing conditions, a sunny location with well-drained soil, where watering ia kept to a bare minimum, is all that desert candle requires. A member of the mustard family (Brassicaceae), its flowers attract bees, moths, and butterflies.
Do you have a gardenia tale to tell? If so, send it along to Joshua@perfectplants.com. Your questions and comments, as well as gardening conundrums and successes, are always welcome.