Crop Guide: Cucumber

Index

1. The origin of cucumbers
2. Botanical taxonomy
3. Nutritional and health values of the cucumber fruit
4. Plant description
5. Growth stages
6. Flowers and fruits
7. Pollination
8. Cucumbers types sorted by final usage, morphology and culture practice
9. Cultivars

The origin of cucumbers

The cucumber most likely originated in India (south foot of the Himalayas), or possibly Burma, where the plant is extremely variable both vegetatively and in fruit characters. It has been in cultivation for at least 3000 years. From India the plant spread quickly to China, and it was reportedly much appreciated by the ancient Greeks and Romans. The Romans used highly artificial methods of growing the cucumber when necessary to have it for the Emperor Tiberius out of season.

Columbus brought the cucumber to the New World, along with many other vegetables. He had them planted in Haiti in 1494, and possibly on other islands. Most of the distinct types of cucumber grown today were known at least 400 years ago. Present forms range from thick, stubby little fruits, three to four inches long, up to the great English greenhouse varieties that often reach a length of nearly two feet.

2. Botanical taxonomy

The cucumber (Cucumis sativus L.) belongs to the Cucurbitaceae family, one of the more important plant families. The Cucurbitaceae consists of 90 genera and 750 species. The genus Cucumis contains nearly 40 species including three important cultivated ones (i.e., C. anguria L. [West Indian gherkin], C. sativus [cucumber], and C. melo L. [cantaloupe]).

Other important crop plants in the Cucurbitaceae family are watermelon (Citrullus vulgaris Schrad), muskmelon (Cucumis melo L.), squash and pumpkin (Cucurbita pepo L., C. mixta Pang., C. moschata Poir., and C. maxima Duch.), and loofahgourd (Luffa cylindrical Roem.). Fig-leaf gourd (Cucurbita ficifolia Bouche) is also cultivated to some extent, but it is even more important as a disease-resistant rootstock in the grafting of greenhouse cucumbers.

3. Nutritional and health values of the cucumber fruit

Table 1.1: The nutritive value of 100 g of edible cucumber

The high water content makes cucumbers a diuretic and it also has a cleansing action within the body by removing accumulated pockets of old waste material and chemical toxins . Cucumbers help eliminate uric acid which is beneficial for those who have arthritis, and its fiber-rich skin and high levels of potassium and magnesium helps regulate blood pressure and help promote nutrient functions. The magnesium content in cucumbers also relaxes nerves and muscles and keeps blood circulating smoothly.

4. Plant description

The cucumber plant is a coarse, prostrate annual creeping vine that grows up trellises or any other supporting frames, wrapping around ribbing with thin, spiraling tendrils. The plant has large, prickly, hairy triangular leaves that form a canopy over the fruit, and yellow flowers which are mostly either male or female. The female flowers are recognized by the swollen ovary at the base, which will become the edible fruit.

The fruit

Botanically, the fruit is a false berry or pepo, elongated and round triangular in shape. Its size, shape, and color vary according to the cultivar (Figure 1.1). In the immature fruit, chlorophyll in the cells under the epidermis causes the rind to be green, but, upon maturity, it turns yellow-white. The epidermal layer may have proliferated (warty) areas, each bearing a trichome (spiky hair). The fruit cavity (three locules) contains soft tissue (placenta) in which the seeds are embedded. The regular cucumber bears actual seeds (seeded cucumber), whereas the English cucumber bears either no seeds (seedless cucumber) or barely distinguishable atrophic seeds. Regular cucumbers are short (about 15-25 cm) and uniformly cylindrical. Their thick, deep green skin has light green stripes and a rough surface with strong trichomes. The skin is bitter in taste and not easily digested, so the fruit needs to be peeled before eating. English cucumbers are long (about 25-50 cm) and cylindrical, with a short, narrow neck at the stem end. Their rather smooth surface has slight wrinkles and ridges. The thin skin is uniformly green and not bitter, so the fruit need not be peeled before eating. The cucumber fruit, like that of other Cucurbitaceae, is noted for its high water content, which is around 95% of its fresh weight.

A strong tap root characterizes the root system and may reach 1 m deep. Overall the root system is extensive but rather shallow; many horizontal laterals spread widely and rapidly producing a dense network of rootlets that colonizes the top 30 cm of the soil and usually extends farther than the vine. Some of the lateral roots eventually grow downwards producing a new system of deeper laterals, which replaces in function the tap root as the plant ages. When the base of the plant is

hilled and favorable moisture conditions exist, adventitious roots arise easily from the hypocotyl as well as from the nodes along the vines.

The large, simple leaves (10-20 cm in the regular cucumber, 20-40 cm in the seedless cucumber) are each borne on long (7-20 cm) petioles. They have five angular lobes of which the central is the largest, and many trichomes cover the surface. At each node above the first 3-5, a simple unbranched tendril grows from the base of the petiole. The sensitive tendrils enable the stems, which cannot twist themselves, to climb over other plants or objects. A tendril tip, upon touching a support, coils around it; then the rest of the length of the tendril coils spirally, pulling the whole plant towards the support.

A cross section of the stem reveals 10 vascular bundles arranged in two rings. The smaller vascular bundles of the outer ring (first five) are located at the angles of the stem; the larger bundles (remaining five) form the inner ring.

Shoot. The main stem of the cucumber plant begins growing erect but soon after assumes a prostrate trailing habit and grows like a vine over the ground. The branching is of the sympodial type (i.e., a lateral bud at each node grows and displaces the main growing point, the latter assuming a position on the opposite side of the leaf). From the nodes of the main axis originate primary laterals, each of which can have their (secondary) laterals, and so on. All stems are roughly hairy, have an angular cross section, may turn hollow when mature, and bear leaves singly at the nodes.

1.5 Growth stages

1.5.1   Vegetative Growth

Vegetative growth consists of 2 Stages:

Stage I – Upright growth is the initial stage that starts when first true leaves emerge and it ends after 5-6 nodes.

Stage II – Vining - starts after 6 nodes. Then, side shoots begin to emerge from leaf axils, while main leader continues to grow. Side shoots are also growing, causing the plant to flop over. Leaves are simple and develop at each node. Each flower/fruit is borne on its own stem attached to the main stem at a node.

Depending on variety and environmental conditions, flowers may begin developing at the first few nodes.

.

Figure 1.2: main development processes and organs developments during first 6 days from germination, under optimal conditions.

1.5.2 Flowers and Fruits

Flower types

There are different flower types:

• staminate (male).
• pistillate (female). Ovary located at base of the female flower.
• hermaphrodite (both male and female).

Cucumbers are monoecious plants which have separate male and female flowers on the same plant (Fig. 1.3, & 1.4). The male flowers appear first and female flowers shortly later. The female flowers have small immature fruit at the base of the flower and male flower do not have any. Pollen is transferred from male to female flower by bees or other insects. When pollinated properly, female flower develops into fruit. There are different types of cucumber hybrids such as gynoecious varieties that produce predominantly female flowers, and seeds of monoecious varieties are mixed with it for pollination. They are very productive when pollenizer is present.

Figure 1.3: Male flower

Figure 1.4: Female flower

Older cultivars, as well as many current cucumber cultivars, have a monoecious flowering habit, producing separate staminate and pistillate flowers on the same plant. Although the terminology is not botanically correct, staminate flowers are often referred to as male flowers and pistillate as female.

Monoecious cultivars first produce clusters of five male flowers at the leaf nodes on the main stem. Subsequently, the plant produces both male and female flowers.

Most current hybrids are gynoecious (all female flowers). Gynoecious hybrids are widely used because they are generally earlier and more productive. The term "all-female" is somewhat misleading as 5% of the flowers are male under most conditions. These modern F1 hybrids have several advantages. As they bear only female flowers the tiresome job of removing male flowers is unnecessary. They are also much more resistant to disease and rather more prolific. There are two drawbacks – the fruits tend to be shorter than the ordinary varieties and a higher temperature is required. Production of female flowers is naturally promoted by the short days, low temperatures and low light conditions of fall. Flower femaleness can be promoted by applying plant growth substances (PGRs) such as NAA (a type of auxin), and Ethephone ( an ethylene promoter).  If a purely female variety is grown, need to provide an appropriate pollinator.

In sensitive gynoecious cultivars, production of male flowers is promoted by long days, high temperatures and high light intensity typical to the summer season. Production of male flowers also increases with high fruit load and with stresses exerted on the plant. Maleness can be promoted by applying PGRs such as Gibberelins as well as by silver nitrate and AVG that act as ethylene suppressors.

Parthenocarpic fruit

There are also cucumber hybrids that produce fruits without pollination. These varieties are called parthenocarpic varieties, resulting in fruits that are called 'seedless', although the fruit often contain soft, white seed coats. Such parthenocarpic fruit set also occurs naturally under the low-light, cool-night growing conditions, and short days of fall. Older plants can also produce 'super' ovaries which set fruit parthenocarpically.

Parthenocarpic varieties need to be isolated from standard varieties to prevent cross-pollination and development of fruits that do contain seeds, and may be deformed by greater growth in the pollinated area.

Greenhouse cucumbers are naturally parthenocarpic.

Male/female flowering sequence

On a normal cucumber plant, the first 10 - 20 flowers are male, and for every female flower, which will produce the fruit, 10 - 20 male flowers are produced. Flowering set progressively at the nodes.

Developing fruit at the lower nodes may inhibit or delay fruit at subsequent nodes.

Size and shape of the cucumber fruits are related to number of seeds produced.

1.5.3 Pollination

Since each cucumber flower is open only one day, pollination is a critical aspect of cucumber production. One or more pollen grains are needed per seed, and insufficient seed development may result in fruit abortion, misshapen, curved or short (nubbin) fruit, or poor fruit set. Hence, 10 - 20 bee visits are necessary per flower at the only day the flower is receptive, for proper fruit shape and size. Therefore, it is important to bring hives into the field when about 25% of the plants are beginning to flower. Bringing in the bees earlier is unproductive because they may establish flight patterns to more abundant and attractive food sources such as legumes or wildflowers. Bringing them in later jeopardizes pollination of the first female flowers. It is important to take into consideration that bee activity is greatest during the morning to early afternoon, and that wet, cool conditions reduce bee activity and causes poor fruit set.

Cucumber varieties can cross pollinate with one another but not with squash, pumpkins, muskmelons, or watermelons.

Pollination in gynoecious ("all female flowers") crops is ensured by blending seed of a monoecious cultivar (pollenizer) with seed of the gynoecious hybrid. Typical ratios are 88% gynoecious, to 12% monoecious. Pollenizer seed is often dyed with a different color to distinguish it from that of the gynoecious hybrid. It is difficult to recognize pollenizer seedlings after emergence in the field. Removing 'different looking' seedlings during thinning may leave the field without the pollenizer.

1.5.4 Cucumbers types sorted by final usage, morphology and culture practice

Cucumber cultivars are usually classified according to their intended use as fresh market slicers, pickles, or greenhouse cucumbers. This classification includes several fruit characteristics such as shape, color, spine type (coarse or fine), spine color (white or black), fruit length/diameter ratio, skin thickness, and surface warts.

Each type should be cylindrical with blocky ends, although rounded ends are also acceptable for slicers.

Pickling cucumbers

"Pickling" refers to cucumbers that are primarily used for processing and pickling. Increasingly, more pickling cucumbers are being sold fresh for immediate consumption. Some consumers have a preference for the pickling type because they have thinner skins compared with slicing cucumbers. Pickling fruits are lighter green in color, shorter, thinner-skinned, and characterized by a warty surface. All commercial cultivars have either black or white spines on the fruit surface, a trait related to fruit maturity. White-spined cultivars are generally slower in their rate of development and retain their green color and firmness longer than black-spined fruits. Cultivars with black spines tend to turn yellow prematurely, especially under high temperatures, and produce larger fruits that soften with maturity. Consequently, black-spined cultivars are used for pickling in regions where summer conditions are relatively cool. White-spined hybrids have largely replaced black-spined cultivars in warmer growing regions and in areas where once-over machine harvesting is prevalent.

For processing cucumbers, the grower generally has little choice of cultivar since the processor selects and provides the cultivars to be grown. Gynoecious hybrids are grown for just about all machine harvest. These types have also replaced many of the standard monoecious types that were previously used in hand-harvesting pickling cucumbers.

• Shorter growth cycle of 50-60 days.
• high plant populations 240,000/ha (60,000/acre)
• Concentrated fruit set adapts them for once over machine harvest
• Predominantly female types (PF)
• Some male blossoms are produced as 10-12% male pollinator seeds are mixed in with the gynoecious types or the PF types).
• An average yield is 25 t/ha* (11.4 short ton or 460 bushels/acre).

*All tons terms in this publication are metric, unless otherwise indicated.

Slicing (fresh consumption) cucumbers

"Slicing" refers to cucumbers that are sold fresh for immediate consumption as a salad item. Characterized by thick, uniform, dark green skins, slicing cucumbers are longer than processing types, and their thicker skins are more resistant to damage during handling and shipping.

Average yield for slicing cucumbers in e.g. North Carolina is 11-14 t/ha (200-250 bushels/acre, but better yields of 33-37 t/ha (600-650 bushels per acre) can be obtained when growing a crop on plastic which is fertigated.

Fruits for fresh market slicing are preferably long, smooth, straight, thick-skinned, with a uniform medium-dark green color. Fresh market cultivars have fewer spines than processing types. For fresh market slicers, both monoecious hybrids and gynoecious hybrids are available. Vigor, uniformity, and higher yields are some advantages of hybrids over previous open-pollinated monoecious cultivars. Regardless of how they are to be used, cultivar differences in earliness and disease resistance are also important considerations for cultivar selection.

Greenhouse cultivars

These should have long, relatively narrow fruits, with rounded ends. Dutch greenhouse cultivars are parthenocarpic with gynoecious expression and high-yield potential, while Japanese greenhouse cucumbers are mostly monoecious. Unlike those for processing and some slicing, greenhouse types are fairly smooth-skinned.

1.6 Cultivars

Varieties of cucumber include both the slicing or fresh salad type and the pickling type (which can also be used fresh), and dwarf-vined or bush varieties. 

Armenian

The Armenian is a long, often much curved type (as noted, actually a melon); owing to its shape, it is sometimes referred to as the "serpent" or "snake" cucumber. It is hard to recommend a particular cultivar, as few catalogues distinguish one "Armenian" type from another.

Oriental

This type is also commonly called "Japanese", though many Oriental nations commonly grow the type (it is also often called "Asian"). It is another long type, usually thin and straight, with a milder flavor than standard types. The Oriental types have many partisans, who find them tender and better-tasting than common cukes (and less bitter and gas-producing), but otherwise generally similar.

Beit Alpha

The "Beit Alpha" (aka mini, hydroponic, snack-size) type (sometimes called "Persian") is an Israeli development (developed a lot of useful hot-weather crops, notably melons and lettuces) whose plants are largely or wholly female, and so do not need cross-pollination. They are thought to have an excellent taste and low bitterness. They are well suited for pickling industry due to short length and solid core, as well as their delicate taste.

More recently, short Beit Alpha; parthenocarpic cultivars have taken over the market, as they are adapted for trellising under protected cultivation. Also, short internodes and set multiple fruit in a cluster habit.

European

The European (aka Dutch, hothouse, greenhouse, hydroponic), fruit develop the characteristic slender, smooth appearance because they are not pollinated. If the flowers are allowed to be pollinated the resulting cucumber fruit will be shorter, bulbous, and irregular and filled with seeds:

• 30 – 35 cm (12 – 14 in.) long
• 3.5 – 5 cm (1.5 - 2 in.) wide
• Thin skinned
• Seedless
• Parthenocarpic
• Gynoecious

Ball and Round

The "ball" types, small spheres (such as the "lemon cucumber") tend to be especially early. Generally, they are thought to be pleasant but rather low in distinct cucumber flavor, but there are some notable exceptions.

Armenian	Oriental	Beit Alpha	Ball and round

Need more information about growing cucumbers? You can always return to the cucumber fertilizer & cucumber crop guide table of contents

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