|The amount of
sun radiation (light intensity
per duration of exposition) present in a given
environment that represents
a potential health threat to
After hardiness ratings,
watering requirements one of the
most important environmental
factors to consider for plants
is the amount of sun exposure they need or can tolerate.
Light is critical for plant
- "Full sun"
generally means that plants should receive and tolerate at least six
hours or more of direct sunlight per
day given that the most intense sunlight occurs mostly in the
afternoon (with a little in the late morning), shadows during these
hours have a big effect on how much light plants receive. Six hours of
direct sun during the morning is very different from the same six
hours in the afternoon. Morning sun, even if it is six hours worth of
direct sun is still not strong enough to be considered anything more
than partial sun (or part shade) The afternoon sun has a stronger
intensity which makes it more powerful.
- "Bright shade"
An environment that receives between 4-6 hours of direct
sun, such as a very bright location with a high, diffuse canopy of
- "Partial shade"
(Also "light shade" or
An environment that receives between 2-4 hours
of direct sunn (morning sun and afternoon shade) or a filtered
a canopy of shade
Species which require some protection from prolonged hot sun, but
which will tolerate some sun . Often these
species prefer morning sun and
- "Full shade"
is an environment with no direct sun exposure or receiving
little direct sun, usually less than 2 hours such as a ground among
buildings or dense evergreen tree growth which often prevent anything
but dappled light from reaching the ground.
Some plants are
particular as to light required while others are more adaptable. Species
that will tolerate only a few hours of morning sun in the summer, if
that. These species will often tolerate considerable winter sun and
generally do well planted so that they can take advantage of the annual
shift in the sunís angle.
Sun exposure requirements that
are appropriated fort mature
plants, may not been suitable for young
seedlings and plants that donít
receiving adequate care (water,
fertilizer). Pay also attention
to ventilation and
heat, plant grown in a
hot green house with a bad air circulation necessitate protection in the
most intense time of the day (11 to 2 pm)
Sun exposure is a very
important planning consideration. Trees, fences, and buildings can all
affect exposure. Matching plants to light levels will go a long way
toward creating a successful and healthy plant collection. Taking time
to see the light of a garden is very worthwhile.
Placing a plant in light
conditions that are outside their ideal range will likely cause
stress and could in extreme cases
cause death. Sun-loving plants growing in shade will be lanky and flower
poorly; shade lovers in sun will probably turn a light green, wilt
easily, and exhibit epidermis
scorch. Make sure that plants to be placed in areas receiving full
afternoon sun can tolerate lots of heat and light.
The intensity of the sun does vary according to geographic location and
period of the year. An afternoon of full sun in Egypt is not the same as
an afternoon of full sun in England. In this case, the distance that
separates the two locations has a considerable effect on the intensity
of light. Plants that might not tolerate full sun in Egypt could be very
happy in England without any protection. And also plants that need to be
grown in shade or partial shade in summer can be grown and take
advantage in a full sun exposure during the winter.
Many plants grow their best in
partial sun (or part shade). In this situation,
temperatures are moderated
slightly and relief from the blazing sun is present for part of the day.
Flowers can last longer and colours often are more intense in part shade
locations. Filtered light during the most intense time of the day (11 to
2 pm) is much more beneficial than any other time of the day. Bright
light (not direct sun) during mid-day often produces a better garden
than full sun in the morning or late afternoon. It is the intensity of
this mid-day light that has the most impact on the growth of plants.
See also: Filtered