Assessing Your Light

Just as they have evolved to thrive in different soil, plants have also managed to find niches in different light conditions. Exotic desert perennials bake in the full glare of the sun throughout the day, while small woodland perennials may receive only an hour or two of dappled sunlight filtering through trees.

Light is a more complicated problem than soil, however, because it is an extremely variable factor. Light can be direct or indirect. Indirect light describes conditions in which the sun's rays first bounce off another object, such as the white wall of a building, or when they light up an area, such as a clearing in a woodland, without directly touching down on it. A woodland clearing would typically receive some hours of direct light and then a good deal more of indirect light.

Light conditions also vary by season and by time of day. Winter light in the northern hemisphere is a "low" light, because the sun is lower in the sky. The sun's rays slant under branches of evergreen first and brighten up areas cloaked in dense shade during the summer months. Similarly, a house corner that faces northwest and is shaded throughout the winter months can be warmed by several hours of sunshine during summer when the sun is high in the sky.

Plants react differently to different types of sunshine, depending on the time of day. Morning sunshine, for example, tends to be cool and refreshing. It seems to waken plants from the quiet restfulness of the previous evening. Hot afternoon sun, on the other hand, contributes even more warmth to an area that might already have been parched by hot, dry weather.

Shade plants, such as hostas, can often tolerate three to four hours of early morning sun but will "burn" (the leaves will brown at the edges) if exposed to that much sun in the height of afternoon. On the other hand, sun lovers, such as New England asters (A. novae-angliae), will flower quite freely with four hours of midday sun but will only bloom sporadically with a similar amount in the first hours of the day.