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Shade is a problem in growing St. Augustinegrass. While the Floratam variety is
notoriously poor in the shade, dwarf St. Augustinegrasses such as Seville, Delmar, and
Jade have a degree of tolerance (Table 1).
Palmetto St. Augustinegrass also looks very intriguing for the shade, but there is
no known scientific comparison data. Whatever variety of St. Augustinegrass is used,
a major problem is in knowing what we mean by "shade."
The closed canopy of broad-leafed trees
(e.g., black olive, citrus, ficus, and oak) transmits only 1 to 6% of sunlight, but
turfgrasses generally need a minimum of 12 to 25% relative illumination (compared with
full direct sun).
You can use your camera as a relative
light meter. A single-lens-reflex camera normally has a light meter in the view
finder. Assuming that you keep a constant ASA setting (film "speed") and
exposure (e.g., 1/30 second), the meter will usually tell you the F-stop, that is, the
size of the diaphragm opening, and hence the shadiness. F-stops are measured in
unusual units, e.g., 2.8; 4.0; 5.6; 8.0; 11; and 16. Every jump to a larger full
unit, say from 4.0 to 5.6, involves a 50% smaller opening or aperture, because the camera
has determined that there is 200% more light . So in the bright sun your camera
determines that a smaller opening (larger number) is needed compared with the shade.
All you need is to find the number of
F-stops difference between sun and shade. So if the camera says 5.6 in the sun, and
4.0 in the shade, that's one F-stop difference, or 50% shade. Two F-stops difference
is 25% shade. To do this properly, point your camera down to a constant background,
such as the same piece of cardboard, placed under the trees, then move the cardboard and
measure down on it again in full direct sun. This way you will be measuring what
light would hit the ground. To be more precise, do this on a cloudy day, using as
your "sun" area a clearing away from the trees. By measuring on a cloudy
day, you will not be bothered by light flecks. If you find three F-stops
difference, your illumination is only 12.5% relative illumination, compared with full
direct sun, and you should probably not attempt to grow warm-season turfgrasses.
This procedure ignores light quality differences in the shade, but is close enough for an
estimate.
| Variety |
Turfgrass quality |
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| Delmar |
6.8 |
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| Seville |
6.0 |
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| Jade |
5.3 |
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| Bitterblue |
4.3 |
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| Raleigh |
4.0 |
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| Floratam |
2.3 |
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Means
of two observations. 10=best, 7=acceptable, 1=worst
Palmetto was not available when this test was
conducted. The experiment was done under 83% shade in a mixed hammock of live oak
and sabal palm at R & D Sod Farms, Okeechobee County, Florida. (Data from Busey
and Davis, 1991.) |
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There's more going on in the shade than reduced light. Leaves grow long and are
damaged by mowers. There is less breeze and less need for water, but more chance
for fungus and caterpillars. The grass grows more slowly and needs less
fertilizer. If you are planting sod which was grown in the sun, it may take several
weeks for all the old sun leaves to die off, and for the turfgrass plants to acclimate to
their new location. As sun leaves begin to die they will be eaten by fungus.
Excessive fertilization and watering of new sod make the leaves tender, and a weak fungus
such as Pythium can be encouraged to move onto the live turf, destroying it.
Besides gradually raising the tree
canopy, which will be beneficial to the turf, the strategies for growing grass in the
shade are to raise the height of the mower, reduce fertilizer, and carefully reduce
irrigation. Growing turfgrass in the shade is often not realistic, but many people
want to try to have a nice carpet at their feet, and tree shade overhead. |
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References
Busey, P. and E. H. Davis. 1991. Turfgrass in the shade environment.
Proc. Florida State Hort. Soc. 104:353-358.
Barrios, E. P., F. J. Sundstrom, D. Babcock, and L. Leger. 1986. Quality and
yield response of four warm-season lawngrasses to shade conditions. Agron. J. 78:270-273.
McBee, G. G. 1969. Association of certain variations in light quality with the
performance of selected turfgrasses. Crop Sci. 9:14-17.
McBee, G. G. and E. C. Holt. 1966. Shade tolerance studies on bermudagrass and
other turfgrasses. Agron. J. 58:523-525.
Peacock, C. H. and A. E. Dudeck. 1981. The effects of shade on morphological and
physiological parameters of St. Augustinegrass cultivars. p. 493-500. In R. W. Sheard
(ed.) Proc. Fourth Int. Turfgrass Res. Conf., Guelph, Ontario, Canada. 19-23 July 1981.
Ontario Agric. Col., Univ. Guelph and Int. Turfgrass Soc., Guelph, Ontario. |
