Growing cucumbers in a high tunnel, 2015

Growing Cucumbers in a High Tunnel
Steve Bogash, Horticulture Educator
Producing and marketing cucumbers before and after the typical field production season has
distinct advantages that can greatly augment the sustainability of a vegetable business. A high
tunnel provides the ideal environment to produce high quality, trellised, cucumbers in the 4-6
weeks before field grown fruit are available and by second cropping the same facility, another
crop that can be marketed in the late summer / early fall as field-grown supplies of cucumbers
are dwindling. These two marketing windows typically provide higher prices as compared to
prices during the field-grown season. In addition, high tunnel or greenhouse produced
cucumbers are typically of higher quality as they have fewer skin imperfections and tend to be
straighter since they are hanging. This article will describe the system used to produce
parthenocarpic cucumbers in the 17’ x 48’ high tunnel at the Penn State Southeast Agriculture
Research and Extension Center (SEAREC).
Definition: parthenocarpic: fruit set that does not require pollination or fertilization of the ovule
to set fruit. When seeds are present, they are sterile. In cucumbers, parthenocarpic varieties
should be protected from pollinators or fruit quality can suffer. The most common symptom
when parthenocarpic varieties are pollinated is misshapen / curved fruit.
The Structure:The high tunnel that this program used is a 17’ x 48’ Ledgewood. It’s been in
place for more than 12 years and has been used for a number of prior projects. In 2011, 12’ of
bows were added to increase the length from 36’ to 48’. Soil from a variety trial of Bell Peppers
introduced the pathogen, Southern Blight, Sclerotium rolfsii, into the soil in 2012. While the
biofumigant Biofence (dry pelleted mustard plants) was applied to the soil at the end of that
season to reduce Southern Blight inoculum, the soil was covered with a heavy geotextile to
facilitate growing cucumbers in nursery pots using an artificial media.
To better manage temperature and improve overall ventilation, a thermostat controlled fan and
louver set was added in early 2013. The roll-up sides are T-handle manually adjusted.
Growing mix and containers: We used similar sized 12” Smart Pots and #2000 / 5 gallon,
EconoGrip nursery pots alternated in pairs in the rows to compare their effects on production.
Note: The 12” Smart Pots require additional potting media of soil to fill as compared to the
#2000 nursery pots. In an earlier trial, we noticed a substantial positive difference in overall
cucumber plant health longer by using Smart Pots. The geotextile fabric that the Smart Pots are
constructed of should increase root gas exchange and perhaps also keep roots cooler as
compared to black injection molded nursery pots of a similar size. All containers were filled with
Frey Brothers #300 potting media. This is a 12-15% coir blend with composted pine bark, peat
moss, and perlite. In earlier trials growing vegetables in containers, it was noted that media
containing substantial coir and composted bark better supported vegetables grown over the
course of a season as compared to peat-lite type mixes. We’ve also had success with Pro-Mix
BRK in vegetable container systems. Other companies offer similar mixes.

Pruning and trellising: Vines were clipped to heavy poly twine hung from purloins. Depending
on the high tunnel design, installing extra purloins and roof support may be necessary. Plants
were attached to the twine using vine clips installed as needed to keep the vines upright and
were pruned to a single vine with one fruiting node left on side shoots. Clips were installed until
the vines reached the purloins, then allowed to hang down. Some growers continue to clip the
vines downward, then back up again if the plants are held for a long time. Pruning and trellis clip
installation can generally be done once per week except during very rapid growth periods when
twice is needed. Remove any side shoot vines that lay on the ground. Senescing or damaged
leaves should be removed regularly during pruning or harvesting to reduce disease inoculum,
increase ventilation and increase spray application coverage.
Fertigation / Irrigation: Water was provided daily at 9:00 and 4:00 PM through a staked
spaghetti drip system. The time varied from 15 minutes per irrigation early in the crop cycle to
up to 30 minutes by the peak of production and leaf area. The emitters provided 1 gallon per
hour per emitter. A proportional injector was used to deliver twice per week applications of 20-
10-20 until the first blossoms were visible, then we changed to 9-15-30 through the end of
production. The rate was based on #.25 of actual N per acre of cucumbers per day. An acre of
cucumbers contains 7,260 plants (1’ plant spacing in row with 6’ between rows). Our tunnel
contained 144 pots with one plant per pot for the spring run, so 144 / 7,260 = .02 acre. .02 x .25
= .005#N for the tunnel per day. Since we started using a 20-10-20 mix that contains 20%N, the
next step is .005 / .2 = #.025 of 20-10-20 per day. Since we applied twice per week take .025 x
3.5 (half a week in days) = #.0875 (40g) of 20-10-20 twice per week. After the beginning of
flowering the fertilizer math would change to: .005 / .09 (9-15-30) = #.056 per day or 3.5 x .056
per application (#.2 or 90g).
Injected fertilizers were supplemented by a pelleted, timed release fertilizer applied to the top of
every pot so that some nutrients were always in the soil solution. Once flowering began, we
applied 4-10-40 at 2T/ gallon foliarly once per week in the tank mix with fungicides and / or
insecticides. Calcium chelate and MagSi were applied foliarly and in the fertigation solution as
needed based on petiole sap testing and tissue analysis.
Choosing Varieties: Your market should determine what type(s) of cucumber to produce. This
program looked at four types: mini’s, standard parthenocarpic, Beit Alpha, and pickling. Each
has distinct market niches plus advantages and disadvantages.
-For growers with traditional markets, the standard parthenocarpic varieties Lisboa and Corinto
are good choices. Both have the dark skin and appearance of a field grown cucumber, have
very few culls and yield well with Corinto generally producing better in our system.
-Urban and farmers markets with diverse clientele may be good opportunities to sell Beit Alpha
(aka. Persian) types like Picolino, Katrina and Socrates. These light green, smooth skin
cucumbers sell poorly in more rural areas. Mini types like Iznik and Unistar sell well in pints in
very urban markets such as Washington DC and its’ suburbs.
-Unless there is a specific need for a pickling type, it is hard to imagine a market where these
are in high demand. The variety Excelsior performed reasonably well and tolerated late fall cool

temperatures better than all other types. Good quality fruit were still being produced with
nighttime lows of 39F (in the tunnel at 36” off the ground) when other varieties were producing
little but culls due to cold damaged skins.
Pest Management: High tunnels and greenhouses are interesting environments to grow
vegetables in as many field-grown foliage and fruit problems are prevented while other pests
find indoor production an ideal environment. Here are pests of high tunnel and greenhouse
grown cucumbers that this program encountered:
-Powdery mildew (PM): This disease is nearly always present in a cucumber tunnel with plants
that are 45 days or older. As humidity increases and plants age, the likelihood of PM increases
rapidly. Plants that are fruiting are much more susceptible to PM than younger plants prior to
fruiting. A proactive preventative fungicide program is necessary due to PM. PM looks like
talcum powder and first appears as pencil eraser-sized spots that spread rapidly.
-Downy mildew (DM):This disease does not overwinter in our area, but does come in annually
on storms from the south. In cucumbers, yellow spots visible on the top of the leaf are usually
the first signs that this disease has arrived. Rapid and timely treatment with a DM pest
management material at the first signs of infection is necessary to avoid premature defoliation of
your plants. These infected areas will continue to senesce even with treatment. Proactive
treatment when DM sentinel sites indicates disease presence can prevent infection. Website for
the DM sentinel program: http://cdm.ipmpipe.org/. DM and PM have no relation except for
sharing the word ‘mildew’ and require entirely different modes of action of fungicides.
-Gray Mold / Botrytis cinerea: Anytime humidity rises indoors can trigger Gray Mold infections.
Flowers and young fruit are especially prone to infection. The best way to avoid Gray Mold is
through improving airflow and ventilation. We are adding a small propane heater to the high
tunnel at SEAREC in order to grow over a longer season and use the heater coupled with the
fan to remove high humidity air. Peroxide products applied during periods of high infection can
help to reduce inoculum.
-Aphids: Aphids are often the first insect to arrive on tunnel-grown cucumbers. We’ve
experienced both Green Peach and Melon aphids. Frequent scouting is necessary as aphid
numbers can increase rapidly under high tunnel conditions. Aphid predators, parasites and
specific aphicides (Fulfill, Beleaf, and Closer) along with biological pesticides such as Met 52
and Grandevo used proactively have readily managed any aphid infestations. As noted in the
Pest Management section below, eliminating the need to control cucumber beetles greatly
reduces the need to apply aphicides.
-Spider Mites:High tunnel crops get spider mites. This is a simple fact of growing in a tunnel
and cucumbers are no different than any other tunnel crop. The dry leaf conditions coupled with
a well-irrigated and fertilized crop are ideal conditions for spider mites. Scout regularly, apply
miticides as necessary (3% M-Pede, Oberon, Portal, Met52, Grandevo, and other materials
found in the latest PSU Vegetable Production Guide) and consider regular releases of mite
predators as a biocontrol measure.

-Striped cucumber beetles (CB):Cucumbers are very susceptible to Bacterial wilt vectored by
cucumber beetles. There is some varietal difference in tolerance to bacterial wilt, but not enough
to use as a management tool. The striped cucumber beetle has always been our dominant type,
but it is not unusual to find spotted cucumber beetles by late summer. Plants die rapidly once
fed on by infected cucumber beetles. This is especially so for younger plants, so control is
necessary from plant emergence though the end of harvest. There are a number of choices of
insectides in controlling CB populations. Rotate MOA using the IRAC code often and include an
aphid management program if using broad spectrum insecticides. The screening noted in the
Pest Management section below is worthy of consideration as it is inexpensive, quick and easy
to install and highly effective.
Pest Management: In 2013, we applied conventional insecticides and miticides as necessary to
control striped cucumber beetle, aphids, and two-spotted spider mites. Managing cucumber
beetles requires using relatively broad spectrum insecticides such as spinosads, pyrethroids
and neonicotinoids. These materials often reduce aphid predator populations resulting in an
explosion of aphids shortly after application. So our 2013 season required either aphicide /
cucumber beetle tank mix or one following the other as aphid populations soared.
Before production began in earnest in 2014, we installed standard mesh window screening over
the roll up sides and intake louvers. This completely eliminated cucumber beetles. No longer
having to spray for CB also reduced the need for aphicides. We were able to reduce aphicide
applications to a single time using Fulfill. Met52 was applied every other week as a general
preventative for aphids, and spider mites.
With the exception of adding a specific DM material when our local Sentinel plot indicated
inoculum present and a specific PM material when we had a few spots on some leaves in the
tunnel, we used the following preventative disease program:
Regalia – Actinovate AG – Stimplex on a 5 day application program (Monday – Friday –
Wednesday, repeat). When DM inoculum was present, we changed to: Regalia + Ranman –
Actinovate AG, plus Stimplex on a 7 day program. If the period of DM inoculum persists,
substitute Tanos, Curzate or Previcur Flex. When PM was present, we used Regalia + Torino –
Cease + GreenStim. There are numerous other PM specific materials, but we had only the
single light outbreak that was easily managed with Torino.
Harvest:We harvested every other day using small pruning scissors on a Monday-Wednesday-
Friday schedule. Not being able to harvest consistently on Saturdays or Sundays due to our
research farm Monday – Friday schedule definitely reduced overall fruit quality due to
occasional overripe fruit. We found Picolino cv. to consistently be the first variety to produce ripe
fruit over our two spring and two fall production runs. The varieties Excelsior and Corinto
produced marketable fruit the longest.
Post Harvest Handling: Beit Alpha cucumbers do not require rapid vacuum plastic wrapping
like the longer fruited ‘Dutch’ greenhouse varieties to extend shelf-life, but do benefit from rapid
cooling or refrigeration. Corinto, Lisboa and Excelsior can all be handled as any standard field
cucumber. Follow all current GAP and FSMA regulations to keep fruit safe to sell and consume.

Marketing:Traditional markets will likely prefer varieties like Corinto and Lisboa due to their
appearance. Excelsior is the one pickling type that has performed well and can readily fill that
niche, but price may be an issue due to modest plant yields as compared to the price that
consumers are willing to pay for pickling-type cucumbers. Mini’s (Iznik and Unistar) and
standard Beit Alpha’s (Katrina, Picolino and Socrates) have a very smooth, light green skin that
is well appreciated in urban markets.
Comments:
1) In order to reduce input costs, we reused the potting media from the spring
production run in the fall. Plants were stripped from the pots including roots and
some potting media, the pots were then topped off with fresh media, inoculated with
Great Grow and replanted with seeds.
2) Direct seeding resulted in very compact plants that were tougher in the seedling
stage vs. transplanted plants. Even using the larger spacing from 50 cell trays
produced some stretching prior to transplanting. Direct seeding made it easier to
install the first trellis clip as the young vines were stronger. Cucumber seeds rapid
germination in warmed soil resulted in only minimal delay of early production. Very
early spring growers may need to use transplants due to lower soil temperatures.
3) We only planted one plant per pot for the spring run which gave us 1 plant per foot of
row. For the fall run, two plants were allowed to flourish per pot. This higher
population produced more fruit per foot with a manageable increase in canopy and
vine density.
This project was supported by Pennsylvania Vegetable Marketing Research Program (PVMRP)
funds. Seeds were provided by High Mowing Seeds, Johnny’s Seeds, and Seedway Seeds.
Potting media was supplied by Frey Bothers. Smart pots were provided by Smart Pots.

Growing cucumbers in a high tunnel, 2015

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Growing cucumbers in a high tunnel, 2015