Posted on by tonytomeo

Sun Scald

Vegetation needs sunlight, but sunlight can be excessive.

It was sad to see the removal of a rather mature but unstable Italian stone pine from the neighborhood. Fortunately, the arborist who removed it was careful to avoid damaging the garden below. Yet, after all the effort, the garden did not remain undamaged for long. The healthy bear’s breech (acanthus) and young Australian tree ferns that had been shaded by the dense canopy of the pine got roasted by the first warm weather.

These perennials got roasted because they were adapted to shade, but could not adapt soon enough to exposure to direct sunlight. This illustrates one of the main problems of topping trees and exposing the interiors of formerly shaded canopies. (‘Topping’ is the disfiguring removal of major portions of the upper canopies of trees.) Like perennials on the ground, foliage as well as stems and main limbs within the canopies of topped trees gets damaged by increased exposure. Although most perennials eventually adapt and recover, topped trees are often damaged too severely to recover.

Foliage can be replaced, but stems and limbs are not so expendable. Deciduous trees and most evergreen trees will replace damaged foliage within the first year. Deciduous trees that get topped while dormant in winter actually do not exhibit foliar damage, since foliage that emerges in spring will be adapted to the exposure that they grow into. However, formerly shaded stems that suddenly become exposed by topping are easily damaged by sun scald, which is like sunburn of the bark.

Sun scald deteriorates into open wounds which leave inner wood susceptible to decay. Minor sun scald of small limbs can eventually be compartmentalized (healed over) before it becomes too much of a problem. Major sun scald can destroy main limbs and even trunks, causing additional disfigurement to trees that were already disfigured by topping! Even if sun scald does not develop, the open wounds left from topping are often too large to be compartmentalized, so remain open to decay.

Regardless of sun scald, topping is more directly disfiguring, by removing well structured limbs and trunks, and causing the development of disfigured and structurally unsound limbs. Secondary growth that emerges in response to topping or severe pruning is weakly attached to the mature limbs that it emerges from because it did not grow together with the mature limbs. It breaks away easily in wind, or simply because it grows too vigorously and soon gets too heavy for weak unions.

Topping actually causes more problems than it is thought to remedy. In some situations, it is actually more practical to remove potentially hazardous trees than to make them more hazardous by topping them.

Posted on by tonytomeo

Sun Exposure Relative To Orientation

Sun exposure changes with the seasons.

Understory plants, which tolerate various degrees of shade, are more popular than ever. Basically, smaller modern gardens amongst larger modern homes are shadier than ever. Densely evergreen trees that provide privacy for such gardens also provide more shade. Sunlight can be scarce. It may be helpful to know where to locate optimal sun exposure.

The sun moves from east to west as each day gets warmer. It does so more or less to the south of vertical. It is a bit farther to the south for winter than for summer. Such orientation and motion determine sun exposure within home gardens. Each side of a house, garage or fence faces one of such exposure or another. Eaves might provide shade from above.

Eastern exposure is good for plants that crave some direct sun exposure but not warmth. Azalea, rhododendron, andromeda and hydrangea prefer such exposures. They receive enough sunlight to bloom, but not so much that their foliage scorches. They enjoy partial shade before sunshine gets uncomfortably warm. Eastern exposures are sunny but cool.

Northern exposure is good for plants that do not require much sun exposure. Hydrangea may be somewhat lanky within such situations. Clivia, elephant ears, philodendrons and ferns may be better options. Upper floors and eaves significantly enlarge the shadows of northern exposure. Shadows are also larger in winter while the sun is lower to the south.

Western exposure is good for plants that crave both direct sun exposure and warmth. It is the opposite of eastern exposures, but is certainly no less sunny. It is merely warmer. Lily of the Nile, lavender, oleander and bougainvillea enjoy such sunny warmth. Some types of ferns and elephant ears may scorch with such exposure. Eaves delay direct exposure.

Southern exposure is good for plants that crave full sun exposure, but tolerate heat. Most plants that enjoy western exposure can also enjoy southern exposure. Many vegetables, with regular watering, are more productive with such exposure. Eaves provide shade for the warmest summer weather. They provide less shade while the sun is lower for winter.