Foeniculum vulgare Mill. var. azoricum (Mill.) Thell.
Apiaceae (sin. Umbelliferae)
History and Origins
The Latin name foeniculum, a diminutive of feonum meaning ‘hay’, perhaps refers to the deeply laciniate leaves or to the fact that at the end of the cycle the leaves dry and turn yellow like hay.
The Greeks called fennel marathon which is thought to derive from the name of the location of the historic battle site which was perhaps, at that time, full of wild fennel.
Cicero named a place in Spain Campus foenicularum (meaning a place or field where fennel grows in abundance); even today in that area, is a Hinojosa del Campo and there are many cities called Hinojos or Hinojosa.
‘Infinocchiare’ (an Italian term meaning to hoodwink, con or fool) has been a common term since the 1400s. No one has yet been able to establish with any certainty the connection of this word to the vegetable. However, the most common explanation may refer to the allegedly common practice of hosts serving their guests food that was seasoned with (wild) fennel to mask the more unpleasant flavors of food and wine.
This same act of “masking” seems to have been exploited by the Puritans in America to cover the smell of whiskey breath.
Fennel contains several flavonoids (rutin, quercetin, kaempferol) with strong anti-oxidizing and anti-radical properties. It also contains anethole, the main component of its volatile oil, which has been shown to have anti-inflammatory and anti-carcinogenic properties.
Diffusion and importance
Italian production is approximately 85% of the world and 92% of European production.
In Italy, thanks to the appropriate combination of climatic conditions that are found in the different regions and varieties with different environmental needs, Italian fennel is eaten throughout the year: cultivations in the center-south produce mainly from September to April; while in the north, from May to October.
Some Italian authors suggest that three botanical varieties belong to the species Foeniculum vulgare Mill.:
var. azoricum (Mill.): Florence fennel;
var. dulce (Mill.): Roman fennel;
var. vulgare (Mill.) Alef.: wild fennel;
Biologic type. Biologically, Florence fennel is generally a biennial herbaceous plant, but is annual when cultivated.
Root system. Fennel has a branched taproot; the roots, although they explore the soil to a depth of 0.4-0.5 m, do not have a great capacity to penetrate into the soil and therefore fennel grows well in loose soil.
Leaves. The leaves are pinnatisect, divided into lacinias filiform in the apical part, formed by a big petiole and an amplessicaule sheath. The enlarged sheaths, thickened, closely imbricated and enveloping a short caule, form the edible and commercial parts of the fennel known as the head (or false bulb).
The head may be up to 15 cm wide and, depending on the variety and the time of harvest, weigh from 250 to 600 g. The head represents 40-45% of the total weight of the plant (the roots 10% and the rest of the leaves account for the remaining 45-50%).
In the “summer” varieties, the leaves that form the head may be few in number (4-6), the leaves are not subdivided and the sheaths are long and narrow, the head is stretched and flattened.
In the “autumn” varieties, the head is made from a greater number of leaves (about 8-10), the leaves are very branched and can grow quite large; the sheaths are short and wide, and the head tends to be spherical.
The color of the head may range from pale green to ivory white, depending on the variety and growing conditions (covering the head protects it from yellowing caused by the sunlight). From today’s cultivars, it is possible to obtain a snowy-white head without the need for intervention during cultivation.
Inflorescence: the transition from the vegetative to the reproductive phase is regulated by the photoperiod (long-day species), which has a critical threshold depending on the cultivar. The flowering stem is erect, branched, and hollow, 0.8-1 m tall, and has a hundred compound umbels composed of 30-80 flowers. The flowers are hermaphrodite, small, and with yellow petals. Fennel exhibits marked proterandry and out-crossing (allogamous) with predominantly entomophilous pollination. Flowering and seed maturation are very gradual. In Italy, flowering usually happens in June-August and the seeds mature in September.
Fruit:The fruit is indehiscent (schizocarp), smooth, oblong, oval or elliptical. The single achene (“seed”) is oblong, yellow-brown, with one face flattened and the other convex characterized, as in other Umbelliferae, by five ribs.
This arrangement does not allow for sowing with a precision sower, so the use of pelleted seed is recommended. The achene has numerous secretory canals that contain the aromatic substances that give the characteristic odor (the main active ingredient is trans-anethole).
Climate and soil requirements
Fennel is a species that prefers mild climates. The thermal requirements are shown in the table.
Germination is a very delicate and difficult phase: in cold soils (early sowing in the field) it is very long (up to 20 days), but also at optimal temperatures it takes about 8-10 days.
Vegetative growth, favored by temperatures between 15 and 20° C, is initially very slow, so that the plant requires about a month and a half to establish itself. The formation of the head is induced not only by the low temperatures, but also by short-day conditions. Fennel has a moderate resistance to cold temperatures; a few degrees below freezing (-2 / – 3° C) can completely destroy the plant; during the harvest, a few days with temperatures of 0° C can cause longitudinal lesions and necrosis to the head that depreciate or completely ruin commercial production. Flowering is favored by long days without an initial marked effect from low temperatures (winterizing is not mandatory). The threshold of the photoperiod varies depending on the variety, but high temperatures and water stress favor the growth to seed.
Water availability is a key production factor; so, during the spring and summer, irrigation is essential.
To get good quality heads, fennel prefers loose soil or medium-mix, that is deep, fresh, fertile, rich in organic matter, not water saturated, and with a pH between 5.5 and 6.8. Heavy clay, unstructured, and asphyxiated soils should be avoided. The sandier the soil is, the higher the weight ratio of the leaves/head. The plant is not sensitive to limestone and is tolerant to boron and magnesium deficiencies. Fennel is very sensitive to the salinity of the soil.
In the garden, fennel is usually alternated with other horticultural crops (pea, bean, potato, lettuces …). It should not be planted after itself or after other Umbelliferae, and should not be replanted in the same ground for 2-3 years. Lastly, following fennel with tomato and cucumber is not recommended.
Varieties and/or commercial types
* Compact head, perfectly white, not very stringy or spongy, roundish, with few axillary sprouts; crispy, tender, sweet, and slightly aromatic sheaths;
* Erect leaves, which allow higher planting density, and a deep green color that contrasts sharply with the white head;
* regular and elongated taproot (positively correlated with a head of good shape and dimensions);
* a well-defined growing season to best organize planting and harvesting;
* morphobiological uniformity;
* tolerance to pre-flowering;
* resistance to cold;
* tolerance to post-harvest browning.Available for sale are local plants, varieties (obtained by genealogical selection) and F1 hybrids.
The local plants, which are named after the place of origin or the adjective of the place of origin (e.g.: Mantua, Marche, Sarno, Romanesco…), have a low morphobiological uniformity. The varieties have good morphobiological uniformity and valuable quantitative and qualitative characteristics. Recently selected and introduced F1 hybrids, have definitively greater production potential both in terms of quantity and quality and improved morphobiological uniformity, though obviously have a higher seed cost (1000 seeds of a variety cost about 1 Euro while 1000 seeds of a hybrid cost 9 Euro). The cultivated varieties have different critical day-length needs for the formation of the head and flower induction, and tolerance to cold that determines the best time to plant on the basis of the different climatic and cultivation areas. Schematically, we can distinguish three main groups of varieties: late, semi-precocious and precocious.
Late varieties: have quite low values of critical day length for the formation of the head; as a result, it can be cultivated only in conditions of decreasing day length (summer sowing in July-August, and autumn-winter harvest from December to March). The cycle is, therefore, long (150-180 days from sowing) and allows the head to grow round and large (600-900 g) with high production. They are subject to the risk of frost damage and development of axillary buds which limits cultivation, especially in the southern areas.
Semi-precocious varieties: their critical day length is high enough to form the head but low enough to induce flowering, so as to allow for the earliest sowing (late June-early July). Their growth is fairly rapid (depending on the weather), the cycle is about 110-130 days, and the harvest is from September to November. Their selection has led to more widespread cultivation in the northern areas due to good levels of production both in quantity and quality (round, heavy, compact heads).
Precocious varieties: These varieties have been selected in Northern Italy (Mantovano strain) or in Switzerland from semi-precocious varieties. They have a high resistance to bolting (thanks to a long-day length that is critical for flowering) which allows for early planting in the spring (February to May), leaving sufficient time for the head to form (the days are sufficiently short) before being exposed to conditions for floral induction. The harvest takes place from May to July-August in the North and in the inland areas of the Center. The cycle is short (80-90 days) and consequently, the heads are medium-small (300-500 g) and the production is quite low even with a high planting density. The heads of these varieties tend to be flattened and oblong.
There are also precocious varieties and hybrids (80-90 day cycle) that are summer sown (late June-July in the North and inland areas of the Center; mid-July to mid-August in the South and coastal areas of the Center) for early autumn production (September-October). These varieties and hybrids, however, are the result of improvement from old late-varieties.
Fundamentals of cultivation practices
The normal planting technique of fennel is direct sowing in the field with further thinning. It is also possible to transplant seedlings with root ball, but this is done only for precocious spring planting and for very late planting (October-November) when, because of the low temperatures, emergence would be too irregular and gradual.
The later the variety (and so having larger plants), the greater the distance between rows, and the lower the density.
Precocious summer-autumn crops are sown in rows at a distance of 0.4-0.5 and the density, after thinning, is 10-15 plants m².
The later production of longer cycle varieties (practiced in the South and the coastal areas of the Center) exhibit higher growth, head size and yield: they are sown in wide rows 0.6-0.8 m to allow for hilling at a density of 6-7 plants m².
The precocious spring crops, which grow smaller, are generally transplanted in rows distanced 0.3-0.4 m at a density of 13-15 plants m².
Fennel has a high nitrogen requirement but it must not be over applied because nitrates tend to accumulate in the leaf sheaths. In a Mediterranean climate, it is irrigated.
It is generally hoed and supported by hilling.
The hoeing should be done during the early stages of the cycle, before the foliage “closes” the row spacing, for the following purposes:
* to control weeds;
* to maintain good aeration of the soil, which tends to form a surface crust.The hilling of the soil at the base of the plant can be performed for different purposes:
* To run lateral-groove-infiltration irrigation;
* To protect the heads from frost, particularly late crops;
* To obtain perfectly white heads protecting them from the greening action of sunlight.The hilling of fennel is generally performed twice: the first immediately follows thinning, and the second when the heads have reached half their final size.
In professional crops over large areas, the harvest is performed with the aid of machines or harvesters.
After harvest, the fennel must be processed (cutting off the roots and leaves), cleaned, immersed in a solution of citric acid (e.g. water and lemon juice), which has antioxidant properties that prevent the browning of the basal cut and of the outer sheaths, and then is cooled with cold water.
The production ranges from 20 to 50 t ha-1, depending on the production areas, the period of planting and the length of the cycle.