Introduction:
The most popular cucumbers grown hydroponically
in greenhouses are the “European” or “Long
English” cucumbers (photo 1). Other cucumbers
becoming increasingly in demand are the Beit Alpha
(BA), Japanese or Persian pickle cucumbers (photo
2). They are similar to the European cucumbers, but
smaller in size, usually 4- to 6-inches in length
compared to the European ones that average from 12-
to 14-inches. These cucumbers are all seedless and
“burpless” in nature with thin skins that
do not require their peeling before serving in salads.
Due to their thin skins, they lose moisture rapidly
so must be shrink wrapped to prevent weight loss.
European cucumbers are the second most important crop
hydroponically in terms of acreage. Unlike tomato
plants that are hardy, these cucumber plants are more
delicate. They must be constantly trained to a special
form (renewal umbrella) to obtain maximum yields.
If left unattended they will quickly entangle in themselves
and production will fall greatly. They cannot be easily
pruned to get their correct form back as what can
be done with tomatoes so correct training is necessary
throughout their life cycle.
Varieties:
All cucumbers grown in greenhouses
hydroponically are of varieties that can be trained
vertically, unlike the regular field varieties that
grow along the surface. The choice of variety depends
on your environmental conditions and the presence
of diseases. I have found for hot, humid conditions
of Florida and Anguilla that it is imperative to select
varieties that are highly tolerant or resistant to
powdery mildew fungus. Some of these varieties include:
“Dominica,” “Logica,” and
“Marillo.” For indoor conditions it is
possible to use other varieties such as, “Millagon,”
“Discover,” “Corona,” “Accolade,”
and “Crusade.” There are many more varieties
that are probably suitable. Your choice will depend
upon the results of various trials you can carry out
under your conditions. For BA cucumbers I have found
the following to be good for our conditions: “GVS
600,” “GVS 601,” (Golden Valley
Seeds), “Nimmer,” (Nirit Seeds), “Darius,”
and “Sarig,” (Hazera Seeds). If you are
growing under conditions of high relative humidity
(RH) be sure to use Powdery Mildew tolerant or resistant
varieties. In your home you should be able to control
humidity and temperatures close to optimum levels
then these diseases will not be as prevalent.
Growing Conditions:
Cucumbers like somewhat higher temperatures
than tomatoes. Their minimum night temperatures should
be about 68 F and during the day maximum temperatures
of 75 to 78 F are ideal. Relative humidity should
be maintained about 75%. Light levels of 5500 lux
(510 foot candles) for 14 to 16 hours per day are
adequate. Carbon dioxide enrichment from 800 to 1000
ppm will help the plants compensate for the lower
than natural sunlight conditions when using artificial
lights.
Sowing:
Similar to tomatoes, cucumbers are
started in rockwool cubes 1 1/2” x 1 1/2”
x 1 1/2” sowing one seed per cube. Be sure that
the seed is placed deep into the hole of the cube
so that it will not dry and at the same time that
will help the seed coat to come off as it germinates.
Be sure to sterilize any flats with a 10% bleach solution
prior to placing the rockwool cubes in them. They
should be sterilized a day before to be sure that
all volatile chlorine is dissipated. Be sure to presoak
the cubes well before sowing. Use raw water for the
first 2 to 3 days until the cotyledons (seed leaves)
fully expand. Thereafter, use a half-strength nutrient
solution. At 4 to 5 days space the cubes in the trays
to double spacing by breaking the cubes apart (photo
3). Do not lie them down on their sides as we do for
tomatoes and peppers. Transplant the seedlings in
the rockwool cubes to 3- or 4-inch rockwool blocks
at 8 days from sowing (photo 4). Space the blocks
in a checkerboard pattern to 9 per flat. Presoak the
blocks well with water before transplanting. Hold
the plants in the rockwool blocks for 7 to 10 more
days before transplanting to the growing area of rockwool
or perlite (photo 5).
Transplanting:
If you are going to use rockwool slabs
as the growing system, soak the slabs for a day, as
was done for tomatoes, prior to transplanting so that
there are no dry spots in the slabs. If you are going
to use bato buckets or other containers of perlite,
it is best to sterilize the substrate prior to transplanting.
Soak the pots of perlite with a Zerotol solution of
a dilution of 1:50 or 2.5 fl. oz. per U.S. gallon
of water. Soak the substrate a few days before transplanting.
Thoroughly drench the substrate several days before
transplanting. Inoculate the substrate prior to transplanting
with “PlantShield” (photo 6). PlantShield
is a beneficial fungus, Trichoderma harzianum, strain
T-22 that is applied to the medium just before transplanting.
It is preventative control for diseases caused by
Pythium, Fusarium, Rhizoctonia, Thielaviopsis and
Cylindrocladium. Drench the pots of perlite at the
rate of 1 to 2 tablespoons per 5 gallons of water.
You will need about 1/3 to _ gallon of this solution
per bato bucket of perlite to thoroughly drench the
medium.
Transplant one European cucumber per
pot with two drip emitters per pot. Place one at the
edge of the rockwool block and the other beside the
plant (photo 7). If you wish to grow BA cucumbers
transplant two plants per pot. Irrigate with one emitter
at the corner of each block with the plant and place
one emitter between the two plants. The irrigation
cycles should be sufficient during the daylight period
to permit at least 25% leachate (drainage) during
any given cycle to keep the nutrient levels in the
substrate stable. Immediately support the plants with
string and plant clips. For more details on transplanting
and the irrigation system, please refer to my book
“Hydroponic Food Production,”
available through my website.
Plant Spacing:
Cucumbers require more space than
tomatoes. The European cucumbers are spaced to occupy
10 square feet of area per plant (photo 8). The BA
cucumbers need about 4 square feet per plant. The
bato buckets are spaced at 6 feet between rows by
16 inches within rows. By transplanting one plant
(European cucumbers) or two plants (BA cucumbers)
per pot we get the correct area per plant.
Training:
European cucumbers are trained very
differently from tomatoes. The conventional method
is the “Renewal Umbrella” system. All
of the fruit and side shoots are removed from the
leaf axils up to the eighth leaf. Then, allow two
fruit to form, then remove one, then permit the others
to form. The plant is usually only capable of supporting
3 to 4 fruit at any given time. When more than that
form, the others will abort. All suckers (photo 9)
and tendrils (stringy growths at leaf axils) (photo
10) must be removed. When the top of the plant reaches
the overhead support cable, cut it off after allowing
two side shoots to form above the wire (umbrella form).
No fruit should be allowed to set where the laterals
will develop. Attach these side shoots over the wire
with a plant clip and permit them to fall down along
the side of the main stem of the plant. Keep on removing
side shoots on these “laterals” with the
exception of one healthy one at the top of the plant
near the support wire. Pinch the lateral once it reaches
4 to 5 leaves. Cut it off close to the top of the
wire where the next “replacement” shoot
is growing after two side shoot start to grow. Continue
this “renewal” process as the old ones
are replaced with new ones. Remove all of the tendrils
on the laterals.
With European and BA cucumbers we
only need to use plant clips to support the plants
every 3 to 4 feet. Wind the plants around the support
string in a clockwise direction always so that you
are consistent in winding. To make this easier to
avoid breaking the plants it helps to pull the string
down as you wind the plant around the string.
BA cucumbers are trained differently
from European cucumbers. Remove side shoots, tendrils
and flowers for the first 5 leaf axils to permit vigorous
growth. Then, allow the fruit to form on the main
stem, but cut back the side shoots to two leaves and
continue taking off the tendrils. When the main growing
point arrives to the support cable above, do not cut
it off, just bend it over and let it come back down.
The side shoots and tendrils are then permitted to
grow without pruning.
You do not need to use Tomahooks with
extra string for supporting the cucumber plants as
they are not lowered. Simply tie the string directly
to the overhead cable or hook. As lower leaves turn
yellow you may cut them off close to the stem with
a sharp knife or pruning shears, but no more than
one leaf per week.
Please refer to my book “Hydroponic
Food Production” for more details of
training methods for cucumbers.
Pollination:
European and BA cucumbers are seedless,
so should not be pollinated. They are 100% female
plants so no male flowers are present to pollinate.
You do not need to vibrate the flowers as you do for
the tomatoes.
Crop Cycle:
European cucumbers take approximately
2 months from seed to first fruit harvest. In commercial
greenhouses the plants are carried for a period of
10 months, generally from January through November
in northern latitudes. In more southern latitudes
such as Florida and here in the Caribbean (Anguilla)
we keep the crop for only 3 months giving us 4 crops
per year. In fact, here in Anguilla we have found
that the cucumbers take only 5 weeks from seeding
to first harvest, so we will change the crops every
2 1/2 months. In your home I would recommend that
you not carry the crop more than 3 months as it gets
very difficult to train and production falls greatly
with the plant age, especially under artificial lighting.
BA cucumbers are in all locations
grown on a cropping cycle of 3 to 4 months. Harvesting
generally begins within 5 to 6 weeks from sowing and
production continues for 8 weeks thereafter. That
will fit 3 to 4 crops per year. Start new seedlings
about 2 weeks before removing the old plants to shorten
the down time between crops.
Nutrition:
When growing hydroponic crops in your
house, you will be growing a number of different crops
such as tomatoes, cucumbers and peppers, so it is
better to use a general formulation rather than a
specific one for that particular crop. Each crop has
different optimum nutrient formulations, but that
is mainly applicable to commercial operations where
the yields are directly related to profitability of
the greenhouse. In your home profitability is not
a factor. You are not going to save money by growing
your own vegetables in your house as you will consume
more electricity and supplies than the potential return
on your production. You must consider growing your
own vegetables as a rewarding hobby that can relieve
stress from your work, provide you with safe vegetables,
and enjoyment of truly “backyard” flavor
in your vegetables.
In the previous article, “Culture
of Tomatoes,” I presented a general formulation
for growing tomatoes and other crops. Below is a specific
formulation for cucumbers. It is presented in Table
1 expressed in parts per million (ppm) of each element.
You would have to calculate the amount of each fertilizer
you require for your volume of tank. You can refer
to my book “Hydroponic Food Production”
to learn how to do these types of calculations.
Table 1. Cucumber Formulation
Element (ppm) |
|
Fertilizer Salt as Source |
| |
Macronutrients |
|
| Calcium (Ca-200 ppm) |
|
Calcium Nitrate |
| Nitrogen (N-140 ppm) |
|
Calcium Nitrate |
| Phosphorus (P-50 ppm) |
|
Monopotassium Phosphate |
| Potassium (K-350 ppm) |
|
Monopotassium Phosphate |
| Sulfur (S-150-250 ppm) |
|
Potassium Sulfate
Magnesium Sulfate |
| Magnesium (Mg-50 ppm) |
|
|
| Iron (Fe-3 ppm) |
|
Iron Chelate (FeDTPA) |
| |
Micronutrients |
|
| Manganese (Mn-0.8 ppm) |
|
Manganese Sulfate
or: Manganese Chelate |
| Copper (Cu-0.07 ppm) |
|
Copper Sulfate |
| Zinc (Zn-0.1 ppm) |
|
Zinc Sulfate
or: Zinc Chelate |
| Boron (B-0.3 ppm) |
|
Boric Acid
or: Solubor |
| Molybdenum (Mo-0.03 ppm) |
|
Sodium Molybdate
or: Ammonium Molybdate |
Similar to the tomatoes, you should
make up a concentrated stock solution for the micronutrients
with the exception of iron as their weights for a
normal strength solution would be too small to weigh
accurately.
pH:
The optimum pH for cucumbers is between
5.5 and 6.0. This is lower than for the tomatoes.
Monitor and record the levels each day using a pH
meter or indicator paper. Adjust the pH as for tomatoes
using an acid or base. Wear gloves and protective
goggles and always add acid to water.
EC:
Optimum EC ranges from 2.2 to 2.7
mS. If growth is too vegetative (too many leaves and
not a lot of fruit) you can increase the EC to shift
the plants to a more generative stage. Permit the
leachate to reach as high as 30%, but lower that if
the plants are too vegetative. If the growth is too
generative, lower the EC and increase the leachate.
Lowering night temperatures will also stimulate generative
growth.
Pests, Diseases & Other Problems;
Cucumbers, like tomatoes, are prone
to numerous pests and diseases. The most severe diseases
of cucumbers are gummy stem blight and powdery mildew.
As mentioned earlier, it is important to choose resistant
varieties, especially for powdery mildew. A number
of mites are very damaging to cucumbers. These include
two-spotted, red-spider mite, carmine mites and broad
mites. Broad mites are extremely damaging to the plants
because they cause the growing points of the plants
to die. They are very difficult to see as they are
almost translucent. We shall discuss pest and disease
problems in a future article. Also, please refer to
my book, “Hydroponic Food Production”
for further descriptions, photos and drawings of these
pests.
Summary:
Cucumbers are a little more demanding
in care than tomatoes, but they will yield highly
under the correct environment and plant training.
The training of European cucumbers is a little more
precise than the tomatoes and mistakes can reduce
production significantly. However, with experience
and some good books on culture you will soon be able
to grow productive plants (photo 11).
