Rain On The Shade Parade

60622thumbModern urban lifestyles are becoming less conducive to gardening all the time. Bigger and taller homes cast larger shadows over smaller garden spaces. The taller fences between these homes do not help. The densely evergreen trees employed to obscure the views of other larger and taller homes also obscure sunlight. Not much sunlight reaches the ground where shorter plants need it.

While all this is going on, we are supposed to be gardening with more sustainable plants that demand less water. Smaller, shadier and more sheltered gardens should naturally use less water than larger and more exposed gardens need. Yet, the plants that do not mind the shade naturally want more water than plants that want more sunlight. There are not many that are drought tolerant.

Drought tolerant plants are naturally endemic to dry climates. Many are from chaparral regions. Some are from deserts. In such ecosystems where water is too scarce to sustain much foliage, there is not much competition for sunlight. Shade tolerant plants are just the opposite. They are from forested ecosystems with taller and shadier trees. Such ecosystems are sustained by rainfall.

There are quite a few plants that do not mind a bit of shade. Heavenly bamboo, flowering maple, hydrangea, camellia, azalea, rhododendron, holly, daphne and andromeda (Pieris spp.) are some of the more familiar shade tolerant shrubbery; but alas, none are drought tolerant. Nor are the various ferns. Even small shade tolerant trees like dogwood want to be watered regularly.

Most of the plants that tolerate shade but are not too terribly thirsty are groundcover plants or perennials. They are not exactly drought tolerant, but can survive with minimal watering because they do not dry out so much in the shade. Once established in a cool shady environment, plumbago, lily turf, periwinkle Saint John’s wort and coral bells (Heuchera spp.) only need to be watered occasionally through summery weather, although they are thirstier in sunny spots. Both English and Algerian ivy need nothing in the shade.

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The Wrong Time For Pruning

80801thumbNot many plants are sensitive to mere heat alone. Actually, many plants prefer warm weather. The difficulty that some plants have with heat locally is that it typically accompanies aridity, and often accompanies afternoon breezes. As appealing as breezes and minimal humidity are to us while the weather is warm, they promote and accelerate desiccation of exposed sensitive foliage.

Pruning, which obviously becomes necessary while warm weather promotes growth, can make plants more sensitive to damage caused by warm, sunny, arid and perhaps breezy weather. It exposes formerly sheltered stems and inner foliage, which are more sensitive than outer foliage is, to more sunlight and drying breezes. Exposed foliage can either desiccate or roast, or both!

A bit of unsightly but relatively minor foliar damage on the extremities of the outer canopy might be only superficial, but major damage can be dangerous. Superficial damage often gets replaced by fresh new growth before it deteriorates enough to expose more foliage and stems below. However, recovery from major damage can be delayed by the distress associated with the damage.

Japanese maple, aralia, philodendron, rhododendron and all sorts of ferns can easily get damaged by increased exposure. Low ferns are not likely to become too exposed by any loss of their own foliage, but often become more exposed by the pruning of plants above them. Like frost damage, foliar scorch might need to be left to shelter remaining foliage until new growth develops.

The bark of many plants, although not susceptible to desiccation, is very sensitive to sun-scald if too exposed. Young and smooth bark is the most sensitive, particularly if it had always been shaded. Scald kills bark and the vascular tissue below. As it decays, it exposes interior wood to more decay that is likely to compromise the structural integrity of the affected stems and trunks.

Pruning during relatively cool weather and while there are a few relatively cool days in the forecast allows foliage a bit of time to adapt to a new exposure before the weather gets dangerous. Through summer, pruning should not be so aggressive that too much sensitive foliage or bark are exposed, even if it is necessary to leave a bit of unwanted sloppy growth to partly shade bark. Aggressive pruning of exposed and sensitive plants should be delayed until autumn, when sunlight is not so intense, and weather is cooler and wetter.

Summer Weather Can Scorch Foliage

80801thumbSevere summer weather is something that we think that we do not need to contend with. It only rarely gets as unbearably hot here as it does elsewhere, and when it does, it usually gets breezy by evening, and somewhat cooler overnight. Aridity, or the lack of humidity, is another advantage, at least for us. The plants in our gardens are affected by warm weather very differently than we are.

Plants will tolerate significantly more warmth than we will, but only in conjunction with humidity. In our climate, we get one or the other, but not often both. In fact, humid warmth is so rare here, that when it happens, it causes spontaneous limb failure in trees that are not accustomed to it. Spontaneous limb failure occurs as vascular activity accelerated by warmth increases foliar weight, but humidity inhibits evapotranspiration (evaporation of moisture from foliar surfaces) that would decrease the weight.

The aridity and breezes that make warmth more comfortable for us accelerate evapotranspiration, which increases the need for moisture. Plants that lack adequate moisture wilt, and the foliage of some can get dehydrated or scorched. Wilted plants recover if watered soon enough. Dehydrated foliage is crispy and can not recover. Severe dehydration kills buds, stems and entire plants.

Scorch is quite different from dehydration. It happens as overly exposed foliage literally gets cooked by sunlight. It is similar to sun scald on formerly shaded bark that gets cooked by sunlight after being exposed by pruning or other means of removal of adjacent vegetation. Scorch is more likely on inner foliage that had been recently exposed by pruning, or foliage near reflective surfaces.

Foliage can not recover from scorch. Damage is permanent, and should not even be pruned away. Just like foliage damaged by frost, outer foliage damaged by scorch shelters the inner foliage. Removal of damaged foliage exposes foliage behind it to subsequent damage. Besides, scorch typically damages only parts of individual leaves, so that undamaged parts continue to function.

Shade Is Not For Everyone

70426thumbThere is no way around it. Just about every garden has some degree of shade. Even low profile single story houses without eaves or fences are shaded on the north side. Eastern exposures get the cooler morning sun. Western exposures get only the warmer afternoon sun. There are vacant and treeless parcels out in the desert that lack shade, but not many of us are gardening out there.

Shade is very often an asset, which is why shade trees are so popular for shading both gardens and homes. Eaves and awnings are architectural features that shade windows and doorways. Arbors, lath roofs and patio umbrellas provide shade for patios where trees are lacking or insufficient. Without shade, garden spaces can get too uncomfortably warm to be useful during summer.

The problem with too much shade is that, although it makes the garden more comfortable and useful for some things, it also makes the garden less useful for gardening. Roses, vegetable plants and most flowering annuals need good exposure. Lawn, the carpeting for some of the more useful of garden spaces, can be sparse where it is too shaded. Sunlight is as important as shade is.

This is one of the many reasons it is so important to select the proper trees for each application. Big trees are nice, but might shade too much area. Evergreen trees that are good for obscuring unwanted views at a distance, will prevent warming sunlight from reaching parts of the home through winter if they are too close. Neighboring gardens and homes need to be considered as well.

Planning functional gardens is of course not always simple. Most of us contend with trees, shrubbery and vines that are too big and shady, either in our own gardens or in neighboring gardens. Climbing vines like wisteria, honeysuckle and trumpet vine, are notorious for growing far beyond their intended applications. It sometimes becomes necessary to remove overgrown or crowded plants, or prune them for confinement. Big plants that can not be contained will limit the choices for other plants that share their space.

Winter Coat

P80117Wire haired terriers know how it works. They wear wiry hair through summer to shade their skin while allowing cooling air circulation. Their softer and fuzzier undercoat that develops in autumn provides better insulation from cold weather through winter.

Beards are not naturally so adaptable, but can be manipulated to function better. Thick beards might insulate and deflect wind through winter. Short beards may not work as well in that regard, but might absorb warmth from sunlight if still darkly colored. As weather gets warmer in spring, beards can simply be removed to optimize cooling air circulation, and eliminate the extra insulation. However, long and gray beards can provide shade without absorbing much warmth from sunlight.

Have you ever noticed that plants that live near foggy coasts or in the lower levels of shady jungles and forests are the darkest green? They want to absorb all the sunlight they can get. Monterey pine, Monterey cypress, coast redwood and the many ferns that live on the ground below them are classic examples.

Plants that live in exposed situations or high elevations are lighter green. Some have glaucous foliage that is shaded gray or blue to reflect a bit of sunlight. Colorado blue spruce, silver leaved mountain gum, century plant and silver sage exemplify this technique. The old man cactus actually shades itself with weirdly elongated spines that resemble gray hair.

English walnut, maple, apple and pear have sensitive bark that would get burned if too exposed during summer. Yet, they are all deciduous and bare through winter. They do not mind, because the intensity of the sunlight through winter is inhibited by the low angle of the sun. By the time the sun is higher in the sky, and the sunlight is more direct (passing through less of the atmosphere at the higher angle), the sensitive bark will be shaded by new foliage.P71019

Plants Are Particular About Exposure

1212121032One of the most important differences between plants and animals is that animals are ‘animated’, and plants are not. Aquatic plants might float about, and might even drift into more favorable situations. Vines and plants with creeping rhizomes can likewise relocate. Otherwise, most plants are confined to the same locations where they grew naturally, or where they were planted. They need to get it right from the beginning.

Most landscape plants that are commonly available in local nurseries are fortunately suited to local climates. A few tropical plants that prefer milder climates, as well as a few plants that prefer cooler winters, can be found; but most plants that prefer other climates are simply unavailable here. Yet, even within their preferred climates, the many diverse plants in our gardens are affected by many other environmental factors.

Exposure is nearly as important as climate is. Some plants need to be completely exposed, while some prefer shelter from heat, cold, wind or sunlight. It all depends on how they live in their natural environments. Some naturally live out in the open. Others live in dense forests, where they need to compete with other plants for sunlight. Even if we do not know where our plants come from, we should know what they require.

Japanese maples are understory trees that naturally grow in the partial shade of larger trees in mixed forests. Some types can do well in full sun exposure, but are likely get roasted by reflected glare, or dry wind. Lace-leaf Japanese maples are more sensitive to exposure, so prefer partial shade in the afternoon, and shelter from wind. However, too much shade compromises foliar color of the red and bronze leafed types.

Most cacti and some types of yucca are just the opposite. They naturally live out in deserts, without any significant competition. In home gardens, they will lean away from shade. Knowing what plants want helps to find the best exposures for them.