xt77wm13ph7v https://exploreuk.uky.edu/dips/xt77wm13ph7v/data/mets.xml   Kentucky Agricultural Experiment Station. 1955 journals 028 English Lexington : Agricultural Experiment Station, University of Kentucky Contact the Special Collections Research Center for information regarding rights and use of this collection. Kentucky Agricultural Experiment Station Progress report (Kentucky Agricultural Experiment Station) n.28 text Progress report (Kentucky Agricultural Experiment Station) n.28 1955 2014 true xt77wm13ph7v section xt77wm13ph7v _ Progress Report 28 ‘I""°’1955
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AGRICULTURAL EXPERIMENT STATION
UNIVERSITY OF KENTUCKY
L E X I N G T O N

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 PROGRESS REPORT ON LOW-COST PLASTIC GREENHOUSES
The second year's use of plastic for greenhouses on the University of
V Kentucky Agricultural Experiment Station Farm has given conclusive proof that
good crops can be grown in such houses. For eight years good crops have been
grown in commercial polyethylene houses at the south edge of Lexington, but no
definite data were kept on the crops. The crops were financially successful and
for this reason it was decided to release the idea to others after definite proof L
was established that crops grew well in them. Seemingly these houses may make
it possible to grow out—of—season crops much cheaper than in glass houses be- »
cause overhead and heating costs are greatly reduced.
i Results with Crops
~ l. Bibb Lettuce.
Bibb lettuce produced extra large and solid heads in much shorter
time than usual. It seemed to thrive under the conditions in the plastic house,
and its quality was very good.
2. Leaf Lettuce.
Grand Rapids lettuce grew well and was of good quality; just as good
if not better than when grown under glass.
3. Kentucky Wonder Beans.
The plants grew vigorously. However, there was a tendency for them
to vine and not set pods, especially if the concentration of nitrogen in the soil was
high. lf plenty of air was admitted and temperatures of 6OOF or more were main-
tained, a good set could be obtained. Plastic keeps the humidity too high if air
exchange is not accomplished.
4. Tomatoes.
Tomatoes grown at the same time, under glass and plastic, were
compared. Here again there was some tendency towards vegetation, but good
fruiting occurred a little later than was true for fruit grown under glass. The
fruits, though about a week later, were larger than when grown under glass am.
were of good quality. The yields have not been completed but appear to be about
equal. There was some tendency towards rotting in the plastic house when air
exchange was slow, but the glass house dried out much more rapidly and there
was less rotting in it; however, there was more tendency for blossom-end rot to
occur in the glass house Blights did not seem to be worse, but there was some
tendency for more leaf mold and sclerotinia rot in the plastic house. This is
not bad if air exchange is kept up on all days possible Fusarium wilt occurred
in the glass house but has not yet been seen in the plastic houses. This was ex—
plained on the basis that the plastic house was on fresh soil, while the glass
house was on old tomato soil. However, fusarium later appeared in a new glass
house located on new soil which had been in sod.

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5. Eggplant. ·'
Eggplant is quite sensitive to adverse conditions, but in a plastic "
house it grew and fruited even better than did tomatoes. .
h 6. Peppers
Peppers grew well. W
7 Cucumbers. 4 `
No extensive tests have been made, but a few vines grew vigorously I
and set a good crop. 'There was not so nnuch mildew as in the glass house.
8. Beets. ' U
Beets showed some tendency to large tops but grew vigorously ’
9. Cabbage.
Cabbage grew vigorously and headed well.
10. Flowers.
About 10 different annual flowering plants have been tried in a small
way and all did well.
Heat and Moisture Retention
The heat build-up from the sun is not so great under plastic as under glass,
but the heat loss at night is less. This is good for plants With the double layer of .
plastic, the loss is less than half that with glass. This was determined by testing
the B. T. U needed in a plastic house. lt was found that 100, 000 B T U kept. the
house at about 60OF when the outside temperature was OOF. By standard methods I
of calculation, glass house of the same size would require 200, 000 B. T. U. It
seems that the best insulation is obtained by maintaining about a Z—to 3-inch dead
air space between the layers. lf the space is much wider, convection currents
cause losses. lf much closer, there is not enough dead air to reduce heat radi-
ation.
Moisture retention is much greater than with glass because plastic has no
laps and is tighter. This lessens the amount of watering needed. lf the houses do
not get air exchange, however, there is more danger of disease. Ventilation and
the application of fungicides are required.
Light fransmission C
The light transmission of the ordinary types of plastic. such as Visqueen,
is about 90 percent of that of glass. With Renolon the transmission is as rnuch as
98 percent of that of glass However, the more ultra—violet light and heat there is,

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the quicker the plastic deteriorates. If put on in late September, it will hold until
the next June. Some new types are being tried which give promise of lasting longer,
but as yet they are not available commercially.
Ventilation
So far, ventilation has been done by side drop vents and by vents in the
gable ends. The difficulty of the side vents is that drafts affect the plants. Since
air exchange has been shown to be very important, it seems that ridge vents should
be made. Of course, the ordinary glass house machinery can be used, but this is ·
expensive. Cheaper methods will be investigated this next year.
A Another way of accomplishing air exchange is to use exhaust fans. These
can be used in connection with the heating system. They can be sued to circulate
T the heat on cold nights. In the day time and on warm nights, air from the outside
can be pulled in and distributed without draft on the plants. A comparison of this
method with ridge vents will be investigated this next year. Gable—end vents
would be installed on all houses.
» Preservation of Wood
The plastic is extended into the ground on the sides, hence, there are no
side walls. Where the supporting 4" x 4" side posts and sash bars go into the
ground, they should be treated with wood preservatives. The plastic, however,
lasts better under ground than above.
Steep Angle Good
The eave plates and ridge bars are made of 2"x 4" lumber. The sash
bars are Z" x Z" lumber. The angle at the eaves should be 400 instead of 330
(standard house) to aid in snow clearance. Removable side post supports should
be used to hold up any snow which may accumulate on the roof.
Heating
Because of its uniformity, the best heat is from hot water fins. lt is
more uniform than steam or hot air, However, the initial cost is high and some-
what more care is required, although the operation can be made automatic.
For small units, the use of gas heaters can be entirely automatic and
the initial cost is low. The heat units (B. T. U.) from natural gas cost somewhat
iriore than those from coal. and those from propane cost considerably more, but
the handling of coal and ashes is costly on small units. For this reason, work is
being done with gas heaters.
lt was found that propane gas, if combustion is complete, gives off only
CO2 and water. lf the CO2 is not too concentrated, it helps plant growth.
lf vents are used, propane works well. The vent;s do not have to be espec-
ially tight so that some CO2 can escape, but a good share goes outside. lf natural

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gas is. used, care should be taken to have tight vents because some types of natural
gas harm plants. Be sure to have burners that give complete combustion. 1ncom— l
plete combustion gives off aldehydes and other products which are harmful to plants.
The Bluegrass Butane Company, 2417 Nicholasville Road, Lexington, Ken-
tucky, has a good burner. The L.B. White Company, Onalaska, Wisconsin, has a
forced-draft burner which is good for large houses. The smaller burner is also
good for smaller houses. They also make blowers for air exchange and hotbed
heaters.
A new heat distributor duct made of pigmented polyethylene is attractive
and is much cheaper than pipe. Plain white plastic can be used but does not radiate A
too well. The first trial using polyethylene laminated aluminum at Lexington gave .
exceptionally good results. Tomato plants set next to the outside grew fine in sub-
zero weather. This was due to the fact that the soil is warmed as well as the air
by this method. These ducts are made by placing wire wickets every Z feet and . _
covering them with plastic., 'The edges are made air—tight by the use of soil. A
blower forces the heat through this tunnel
Fastening the Plastic On `
It is best to run the plastic the long way. lf the house is 84 feet long, 85 V
feet of the plastic is rolled on a pipe or stick 6 inches longer than the plastic on
each end. One man tacks the plastic at one gable next to the top. The other takes
hold of the roll and rolls out 6 or 8 feet, or over 3 or 4 sashbars, and pulls tight-
ly on it. The other tacks the lath on down to 8 inches of the lower edge. The next
length is placed under the 8 inches so that there is a lap of about 6 inches, and
tacked in the same way. If the lap is about 6 inches and the plastic is pulled tightly,
there is no need of sealing the laps since they will stay together even in strong
winds. The inside layer can be put up with paper disks and tacks since the wind
does not get to it.
New Plastic House on the Station Grounds ·
A second house was tested this spring It was covered with Reynolon and
Shellmar sheeting. [`he Reynolon admits more light than any of the plastics be- U
cause it is clear. Shellmar sheeting was clearer than Visqueen It seems that
both of these polyethylene plastics held up exceptionally well and plants did fine
under them.
Sources_i>_f_Plastic
A Louisville firm makes polyethylene plastic especially for greenhouses; it
is Peter and Company, 3618 Lexington Avenue. Box 12, Louisville 6, Ky, Con-
venient rolls of the right width and thickness are available.
Other sources of plastic in large amounts include E 1. DuPont DeNemours _
& Company, Film Department, 1007 Market Street, Wilmington Del (56 inches is
the widest they have). A firm having 72.—inch material (Shellmar sheeting) is Con—
tinental Can Company, Mt Vernon, Ohio Another product, which is somewhat
clearer, is called Reynolon. This can be obtained from Reynolds Metals Company
(Do—lt—Yourself Division) Louisville, Ky The Viskzng Corporation has plastic of
'  `  • • cost of wider widths is some what higher Medium-wide

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Widths are easier to put on 'The O OO3" gage is available, and under some con-,
ditions, especially at the top of the greenhouse, it may be good to use this heavier
: gags
( Mention of commercial products in this report is made only for pur-
poses ot information The Agricultural Experirnent Station does not guarantee
nor warrant the standard ofthe products and the use ofthe names in this report
does not imply the approval of these products to the exclusion of others which
may also be avazlable  
_· Cost Estimate
Since the proiect has started, the cost of plastic has dropped about 12 per-
cent To cover an l8‘ x 84" house, the cost as only about $24 for the outsade layer
of O OO2" plastic and $1*5 for the inside layer of Ot OOl‘3" plastic This is based
on large quantity; wholesale prices Plastic ctn small amounts costs more The
framework cost varies fz om $1*50 to $250
» A bluepr.* University of Kentucky, Lexington. Kentucky, for 10
cents
E M Emmert
Professor of Horticulture