FOR THE RECORD:
Shades of green —An article in last week's Home section on the biology behind the different colors in the garden said plants exposed to only dappled light put less nitrogen into photosynthesis. The plants, in fact, put less nitrogen into photosynthetic enzymes, which inhibit photosynthesis. More nitrogen is put into chlorophyll, which explains the deep green color.
Seeing green in the country can ruin it for you in town. Back in the city, the perfectly harmonized greens of the wild give way to an exotic cacophony. Olive trees with their leathery dark foliage and silver undersides sit in Irish green lawns. Yellowing citrus trees are coupled with blue-green fan palms. Feathery New Zealand tree ferns are partnered with birds of paradise.
Flower bed after flower bed, we display horticulture's answer to culture clash. If they were animals and not plants, the incongruity would be obvious: a camel and a seal, a tiger and roadrunner, a kiwi next to an elephant. But because they're plants, the only hint that they need different nutrition, sun, water is the color of their leaves. Their greens clash. They are hotbeds of green-on-green violence.
What at first might seem an aesthetic preoccupation is in fact a biological one. When greens clash, generally a plant is in the wrong place. Olive trees capable of living thousands of years will be lucky to last five in the sprinkler zone of a lawn. Learn how to read green, and more often than not, you don't even need to know the name of a plant to know whether it belongs where it is, whether it's healthy, stressed or dying. The pallor of the foliage amounts to nature showing the gardener how a plant is doing.
The art of the gardener is noticing.
David Lee, a professor at Florida International University in Miami, has been studying leaf color and function a quarter century. Leaves, he explains, are disposable "optical organs" in which plants harvest sunlight. Part of the green that we see on a sunny day is the glow radiating out from within those fluttering factories, where it is the job of the green pigment chlorophyll to absorb the light to use for energy to drive photosynthesis.
Two other compounds — carotenoids and anthocyanins, or more simply, yellow and red pigments — work alongside the chlorophyll. These backup pigments are thought to help deal with excess light, Lee explains. A leaf can only use roughly one-third of the light that hits it. The rest must be deflected so that the leaf doesn't burn up. These yellow and red tones are most welcome in new leaves, such as the pale frond of a young fern, or the fresh shoot of a rose bush. A slow release of chlorophyll into tender leaves allows them time to mature before demanding that they be up and photosynthesizing.
Yellows and reds in mature leaves return as preludes to death, the colors revealed as the plant pulls nitrogen, and with it the chlorophyll molecules that nitrogen helps comprise, back into the wood.
Beyond pigment, any number of variations in leaf structure affect how colors concentrate and light reflects from the plants, hence the shade of green that we see. There are big leaves, small leaves, flat leaves, curled leaves, leaves shaped like needles, lacy leaves, thin leaves, thick leaves, pale leaves, dark leaves, reflective leaves, scaled leaves, waxy leaves, fuzzy leaves. There are so many variations precisely because plants need all the survival strategies they can get, says John Gamon, a botanist at Cal State L.A. Unlike us, they can't get out of the midday sun. "Plants can't get up and run away," he says.
Harvard University biologist Noel M. Holbrook chooses the deciduous forests of the East, with their maples and beeches, to contrast with California as an example of how highly adapted indigenous leaf types are to their locales. Back East, she says, the mountain ranges are covered by deciduous forests whose trees have flat, porous leaves with fast growth, fast hydraulics, fast energy conversion and fast lives. The leaves are born in spring and dead by fall. By contrast, we don't have Eastern-style autumn leaf shows in California because the tender leaves of those dramatic maples would never make it to September. For a tree to hack it out west, its leaves need to be adapted to high light and low water.
As a rule, the leaves of indigenous Western trees tend to be smaller and tougher. The botanical term, a good Scrabble word, is sclerophyllous, from the Greek skeros for hard, and phullon for leaf. Pine needles and stout little cupped leaves of our western live oaks are both sclerophyllous.
The bigger an investment a plant makes in a leaf, the longer that leaf needs to last. In contrast to the ephemeral leaves of the East, the sclerophyllous leaves of the West are shed so slowly that they earn the plants the term "evergreen." Yet they are not greener. If anything, they are less green, tending to the gray, the blue, the silver, the olive. The chlorophyll may be the same as chlorophyll back East, but the thickness of the leaves combined with protective coatings give rise to a dusky Pacific palette. It can seem as if there is no end to their mechanisms for scattering light: hairs diffuse it, wax reflects it, scales bounce it every which way. These nifty defenses even extend to annuals. The seemingly delicate leaf of the California poppy appears slightly blue because of a protective film of wax.
The dusky Western leaf tones are in good company. They repeat themselves across the cradle of civilization, the Mediterranean basin, and wherever one finds similar climates — in central Chile, western Australia and the western Cape of South Africa. Here cross-cultural references can work, because crudely summed up, the Chilean, Australian, South African, Californian and Greek floras all have the same drinking habits and tolerate similar amounts of sun at comparable times of year. Tonally and ecologically, plants from most of these places work in California gardens. The trick is embracing them. Part of the shyness might even be that it feels vaguely un-American. Can it really be right that an Iraqi date palm sits in a Californian garden so much better than a Virginian dogwood and lawn?
There is no discussing the use of green in California gardens without stepping into the minefield about the rightness or wrongness of the suburban lawn. As the dinner party sociologists have it, the ubiquity of fast, wet, garish grass in Los Angeles is a case of the new West craving old Eastern respectability. Perhaps.
However, before accusing anyone of attempting a mini-Monticello in Monrovia, it would be an interesting experiment to try to buy a new house without a miniaturized approximation of a Jeffersonian green lawn around it. Getting a developer to leave out the lawn is like asking an automaker to leave out the polish. What grows faster than grass? Lawn is the cheapest instant garden to install, so developers slap it in with a sprinkler system to damp down dust around newly built homes. It then falls to the homeowner to pay up front to have the lawn removed, or pay later in the form of bills for daily water, weekly mowing and city pickups of the rotting clippings.
THIS is where it helps to be able to read green. If the landscaping decision is in favor of wet bright greens, then the challenge is to find plants that can take up enough water to keep up with California sun without wilting, have moderate enough growth that they don't turn gardening into a mowing and pruning treadmill, and whose bright undertones work together. Iochroma, pineapple sage and any of the many broad-leaved South American salvias can live with lawn and keep the garden clicking with hummingbirds.
If the decision is in favor of the dusky, darker native palette, then it's useful to select some middle greens — desert honeysuckle, rosemary, California gooseberry, mallows and even tea roses — that can pick up the lighter tones from neighboring yards. This will create visual connections with the landscape.