cucumber

INTRODUCTION
The cultivation area of cucumber in South East Europe (SEE) is almost 2 000 ha
and it is the second greenhouse vegetable in the region after tomato. An additional
area of > 700 ha is cultivated under tunnels.1
INFLUENCE OF ENVIRONMENTAL FACTORS
Cucumber is a typical subtropical plant and grows best under conditions of
high temperature, humidity, light intensity and nutrient availability; it is highly
sensitive to unfavourable environmental conditions.
Temperature
Air temperature influences vegetative growth, flower initiation, fruit growth and
fruit quality. Cucumber growth rate depends on the average 24-hour temperature:
the higher the average temperature (≤ 25 °C), the faster the growth. Optimum
air temperature depends on the growing period. At germination, the optimum

temperature is 25–35 °C and, with good moisture, it takes 2–3 days for seeds to
germinate. In contrast, at 12 °C, seeds need 12–20 days to germinate and there are
many losses. Shoot growth does not occur at air temperatures of < 13–15 °C, while
the maximum temperature for vegetative growth is about 38–40 °C.
During the first week after planting, the ideal air temperature is 22–24 °C;
thereafter, temperatures should be kept at 20–22 °C until the beginning of harvest.
During warm weather, in late spring and early fall and at harvest, it is recommended
to lower the air temperature settings by ≤ 2 °C to encourage vegetative growth,
especially at night. At higher air temperatures, fruits grow rapidly and compete
for assimilates. A longer harvest break may begin, particularly after harvesting
cucumbers from the main stem. This can nullify the advantage of an earlier
start to the harvest; in addition, plants get older earlier. For good fruit quality,
temperatures should be 22–24 °C; at temperatures of < 18 °C, fruits tend to be
shorter.
A day/night temperature difference is recommended for winter and early
spring cultivation only. Growth performance depends on the 24-hour mean
temperature during the long days and short nights of spring/summer. Lowering
night temperatures in this period is of no physiological advantage for the plant; it
could, however, be done to save energy.
Soil temperature is important, in particular at germination and the youngplant stage. If soil temperature remains < 14–16 °C for a long time, plants wilt and
then die. For this reason, cucumber is said to need a “warm foot”. Soil heating
enables cucumber plants to better endure low air temperature, but this practice
is not adopted in SEE countries. Low soil
temperatures stimulate soil-borne diseases
and reduce the water and nutrient uptake
ability of roots, particularly uptake of
phosphorus. A minimum root temperature
of 19 °C is required, but 22–23 °C is
preferable.
Water temperature in irrigation must
also be controlled and adjusted to avoid
the appearance of cold shock symptoms
(Plate 1). Heat injuries will appear under
high transpiration and with inadequate
water supply after 1–2 hours (Krug et al.,
2002).

Light
Temperature control must be considered in the context of light intensity.
Radiation affects total plant leaf area, carbohydrate production and, consequently,
productivity. During the winter, the carbohydrate supply is low and productivity
is reduced, resulting in many aborted fruits. Light also has a direct influence on
fruit quality. For example, fruits grown under low light conditions have less dry
matter, are generally light green at harvest and easily turn yellow on the shelf.
Young fruits are usually more sensitive to low light intensity than older fruits on
the same plant.
Humidity
High humidity used to be generally recommended for greenhouse cucumber.
However, high humidity is only appropriate if the water supply is periodically
insufficient, because it is important to maintain continuous moisture. High
relative humidity increases the risk of water condensation and the development
of plant diseases, while low transpiration rate leads to inadequate absorption
of nutrients (Krug et al., 2002). ‘Beit Alfa’ cultivars have good tolerance against
powdery mildew. A combination of high daytime and low night-time humidity is
recommended for optimal cucumber fruit production and quality.
CO2 enrichment
A decrease in CO2 below the concentration in the outside air should be
avoided. The recommended concentration is 600–800 μmol mol−1 to increase
cucumber yield, although higher concentrations are found in the literature. The
concentration of CO2 applied depends not on the conditions, but on the incurred
cost. If there are no industrial CO2 sources in the vicinity, decomposition of
manure or other organic products, such as straw bales, is an effective method.
Indeed, the traditional straw bale cultural technique has long been adopted in
cucumber cultivation, and it is one of the oldest and simplest methods of CO2
enrichment in greenhouses.
Soil requirements
Cucumber requires a deep, well-drained, structurally stable, fertile soil with high
pore volume. High porosity and stability are important for coping with high
and frequent water supply, as well as with stress due to agricultural practices and
harvesting. This can be achieved by incorporating large amounts of organic matter
and adopting proper tillage measures. Compact, cold soils with a high level of
groundwater are not suitable for cucumber. Sandy loam soils with a pH of 5.5–6.5
are more suitable.