Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR ACCELERATING PLANT GROWTH WITH A
PROTECTIVE COVERING
Field of the Invention
The present invention relates to horticulture. In particular, the invention
relates to
a method for accelerating the growth and germination of turf, decorative
plantings
and other plantings by covering same with a covering having selected
properties.
Background of the Invention
Growers of turf and other plantings, particularly in northern climates, often
wish to
get an early start on the season. Businesses such as turf farms, golf courses,
resort hotels and the like, place a high economic value on an early start to
the
spring growing season. Unfortunately, a combination of frost, desiccation, and
low
soil temperatures can severely inhibit early season plant growth. Thus, it is
desirable to provide a means by which such commercial operators may encourage
growth of sod and other plantings despite inclement conditions. The same
requirements apply to persons who grow sod in areas of high use, including
sports
facilities such as golf greens, playing fields or grass tennis courts, or as
well as
parklands and other grounds which experience high wear. As well, many
homeowners have a desire have a green and lush lawn for as long a season as
possible. As well, groundskeepers for athletic fields and the like often are
required
to rapidly regrow turf after an athletic event. For all of the various needs
outlined
above, and others, there is a need for a method to rapidly and easily
accelerate the
normal pace of growth of turf and other plantings.
It is known to cover turf, seed beds and other young plants with a tarp which
permits the passage of light. For example, U.S. patent 5,070,643 (Hinsperger)
discloses a method for protecting outdoor areas of grass and other plants, by
covering the area with an open weave material. The material is U.V. stabilized
plastic covering which permits the passage of at least a portion of sunlight.
A
covering of this type serves to protect the underlying ground from elements,
such
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as driving rain, hail, light snow, and the like. As well, a "green house
effect" may
be achieved whereby the sun's warmth is trapped beneath the cover, to more
rapidly heat the underlying soil, and further to provide slightly insulative
qualities
to minimize overnight frost damage. This method provides benefits over the
absence of any protective covering, but still does not achieve the rapid
growth
which may be required by golf course developers and others who achieve
significant economic benefits by achieving rapid early season sod growth.
Thus,
there is a need for an improved method for achieving rapid sod and other plant
growth.
The use of coverings to protect turf repre~~ents a balance of various factors.
In
particular, in order to prevent soil overheating during daylight hours, the
cover
must block a portion of the sunlight. For example, in Hinsperger's patent
5,070,643, the cover comprises a lace coating, approximately thirty percent of
which is covered by a non light-transmissible layer. Thus, somewhere in excess
of thirty percent of the sunlight is blocked. In the absence of such blockage,
the
plants under the cover would be killed by excess heat on sunny days. At the
same time, sufficient light must reach they plants to permit growth. Further,
the
cover must be durable while at the same time being sufficiently thin to
present
easy handling and storage of large coverings.
In light of the above requirements, it is an object of the present invention
to
provide a method for expediting the gro~nrth and germination of sod and other
plants such as flowers and vegetables. 't is a further aspect to enhance such
growth, by providing a protective layer against the elements which also
permits
the passage of sufficient sunlight for ma:~cimal plant growth.
Summary of the Invention
In light of the above objects and requirements, the present invention takes ad-
vantage of the high degree of selectivity of most plants in the light
wavelengths
which are effectively absorbed and usecl by the plant. In the present
invention,
the covering is provided which permits the transmission of light of select
wavelengths
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while blocking the passage of otherwavelengths. Careful selection of
transmissible
wavelengths permits the material to block sufficient light, particularly
infrared and
near infrared spectra, to prevent overheating during daylight hours, while at
the
same time permitting the passage of light in the useable spectra to maximize
plant
growth. Specifically, it has been found that a covering may permit
transmission of
light in the green spectra, having a wavelength of between approximately 475
nm
and 575 nm, while significantly blocking other wavelengths. This transmission
of
l0 light in spectra which are optimally absorbed by plant chlorophyl of the
target
species, while blocking a large portion of wavelengths which lead to
overheating.
Thus, according to one aspect of the invention, a covering is provided for
protecting turf or other areas planted with a desired plant species,
comprising a
lightweight, one piece cover formed from a material which permits the
transmission
of light in the spectra having a wavelength of between 475 and 575 nanometers,
and substantially blocks the passage of light having a wavelength less than or
greater than this range. In a preferred version, the material comprises a
woven
plastic fabric.
In a further aspect, the invention comprises a method for protecting plant
growth
against the elements while encouraging plant growth and germination,
comprising
the steps of:
providing a one piece cover formed from a material which permits the
transmission
of light in the spectra of between 475 and 575 nanometers, while substantially
blocking the transmission of wavelengths below and above this range, said
covering permitting the passage of air and moisture through openings within
the
material; and
covering the surface of the soil with said material.
Preferably, about 12 - 14% of light in the 530 nm region is transmitted; with
the
transmission fading off to 2 - 4% at wavelengths more than 100 nm above and
below this peak.
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In one aspect, radiation below 450 nm and above 650 nm is transmitted at less
than 5% of incident light.
In another aspect, radiation in the red and near infrared spectra (i.e. above
680
nm) is transmitted at between 2% and about 4% of incident light, to permit a
controlled amount of greenhouse heating.
to Desirably, the cover is formed from a woven plastic material which permits
the
passage of air and moisture there through, while having a sufficiently tight
weave
to retain suitable insulative qualities to minimize frost damage to the
plants. The
material may comprise an open weave scrim formed from polypropylene, which
optimally is laminated with a striped lace coating formed from a plastic
material
compatible with the polypropylene of the strips.
In a further aspect, an area of outdoor grass or other plants may be protected
from
desiccation and winter kill, by increasing turf temperature and stimulating
early root
and top growth by covering the area in the fall with the cover characterized
above,
20 securing the cover in position, so as to remain in direct contact with the
underlying
soil or plants, and maintaining the cover in contact with the plants during
winter
months. The cover is then removed in the spring after all danger of frost has
passed and average temperatures are sufficiently high to permit suitable rates
of
plant growth.
In a further aspect, the method may be used to quickly repair by regrowth
damaged
turf, such as playing fields or golf greens in mid-season. In this aspect, the
method for encouraging plant growth may comprise the step of placing a cover
as
characterized above, on a turf covered area at a time of year when normal
rapid
30 . turf growth occurs. The cover is left in position for a period of about
one week or
less, or alternatively for about two weeks or less to provide short-term,
accelerated
turf recovery.
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Having thus generally characterized the invention, the invention will now be
further
described by way of a detailed description of the preferred embodiments
thereof,
and by reference to the accompanying drawings.
Brief Descnj~tion of the Drawings
Figure 1 is a plan view, from above, of an area of turf covered by a covering
according to the present invention;
Figure 2 is a more detailed view of a portion of a covering according to the
present
invention;
Figure 3 is a schematic view of a cross section of a portion of covering
according
to the present invention, illustrating graphically the selective transmission
of light
radiation there through;
Figure 4 is a graph showing the selective transmission of light of a spectrum
of
wavelengths through a covering according to the present invention.
Detailed Description of the Preferred Embodiments
Figure 1 illustrates a covering 10, staked to the ground 12 over a region of
turf
such as a golf course putting green or the like. Conveniently, the covering,
comprises a plurality of panels of convenient size, stitched together to form
a one
piece covering of a suitable size to cover a desired area of grass.
Essentially, the
only limit to the size of such a covering is the ease of handling of a large
covering.
As will be discussed below, the fabric material which forms the covering is
relatively thin, thus permitting the use of a large covering without undo
difficulty in
handling and storage. The porosity of the covering makes the handling easier,
especially folding of the tarp, since air pockets will tend not to be trapped
within the
tarp.
The periphery of the covering is staked to the ground, by plurality of stakes
16
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spaced apart by a desired amount. Such stakes may be joined to the tarp either
via cords 18, or the stakes may be simply passed through grommet openings 20
within the tarp 10. Alternatively, if thin wire stakes are used, the stakes
may be
simply pushed through the fabric.
In a convenient method of application of the covering, the covering is removed
from storage and unfolded or unrolled over the turf, in the fall months after
the
growing season has ended. The covering is then permitted to remain in position
over the winter. The covering experiences little damage from snow or frost.
The
covering is then permitted to remain in place during the early spring months
when
turf growth commences, encouraged by the protection given by the tarp. The
covering may be removed when the minimum daily temperature exceeds 0°C,
i.e.,
when the risk of overnight frost is substantially gone.
The covering acts as a filter to screen out certain frequencies of light, and
permit
the passage of other frequencies. As will be seen in Figure 4, maximal
transmission is permitted for light between the wavelengths of about 475 to
575
nanometers, with a peak at approximately 530 nanometers. Transmission falls
off
rapidly above and below this range. The optimal range is within the green
colour
of the spectrum. At 530 nm, transmission is between 12 -14%. This falls off to
8 -
10% at 475 and 575 nm, and to 2 - 4% at wavelengths below 430 nm and above
630 nm. However, as seen in Figure 4, red and infrared radiation (680 nm and
above) is transmitted at a higher level to permit a degree of green house
heating.
It has been found that the provision of a covering having the above
characteristics,
provides optimal plant growth while minimizing overheating due to a
"greenhouse
effect' when strong sunlight strikes the covering.
Conveniently, the covering may be permitted to remain on the ground surface
during the early spring, and removed when the weather is sufficiently warm to
permit natural plant growth without the inducement of the covering. As well,
it may
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be convenient when such a method is used on, for example, golf courses, to
remove the covering during hours of operation of the golf course, and replace
it on
weekdays or after hours to further encourage turf growth.
It will be seen that the light transmission properties selected for the
covering
permits transmission of a small but noticeable quantity of light in the red
end of the
spectrum, thereby permitting a degree of green house warming. However,
blockage of a significant portion of light in this end of the spectrum
prevents
overheating during daylight hours, while at the same time preventing excessive
losses due to radiation at night {particularly on clear nights), thereby
preventing
frost damage during nights of hard frost and maintaining a suitable soil
temperature for plant growth.
The covering is conveniently fastened to the ground, by one or more of the
methods described in U.S. patent, 5,070,643, including forming an inward fold
around the perimeter of the cover to provide a strengthened region to hold an
array
of stakes, or providing straddling cords or straps to extend across the cover,
and
staking these cords, to prevent billowing in the wind. Cords, straps or webs
may
criss-cross or be diagonally disposed on the cover. The cords may be staked by
V-shaped stakes, which straddle the cords.
The methods described above may be used either to encourage the growth of
existing turf, or to speed up germination and early growth of newly-seeded
areas.
Alternatively, the covering may be placed on a region of turf which has been
damaged, for example an athletic field or a golf green. For this use, the
cover is
positioned on the turf during a period of non-use, which normally would occur
during the normal turf-growing season. The cover is left in position for a
relatively
short time, e.g. about one week or less. This method provides a rapid means to
repair and re-grow sod which has experienced a measure of damage, but not so
much as to require complete re-sodding.
