Leek and shallot 371
In the Netherlands, Albana, Alba, Alma-902, Jolant, SG 446 and SG 448 were
considered better. Albana has the highest yields and crops early. Alba and Jolant have
dark-coloured leaves and an upright habit. Alma-902 and SG 446 are not so high
yielding but leaf colour and habit are favourable (Aalbersberg, 1985).
Twenty leek cultivars were assessed for possible production in coastal British
Columbia. Among the early leeks (harvested in October), Colonna, Longa, Odin and
Kilima all yielded over 40 t/ha of trimmed, marketable leeks. Their marketability
when harvested in January ranged from 0–16 t/ha. Among the winter-hardy cultivars,
marketable yields in October and January were not significantly different but there
was a marked increase for the April harvest. Cultivar Goliath, for example, yielded
23 t/ha in October and January and 33 t/ha in April. Other good winter-hardy cultivars
include Siberia, Artico and Derrick (Maurer, 1982).
22.3.2 Climatic requirement
Leek is a relatively long-season crop requiring about 120 days from seeding to
harvest. It is generally more cold-tolerant than the onion in its early development, but
it can be damaged at harvest by frost (Swiader et al., 1994). Most leek cultivars will
grow at least reasonably well wherever the crop is produced. The main reason for this
great adaptability of the leek is that it neither forms bulbs nor enters a rest period, as
does the common onion, but continues growth and can be harvested over a long
period of time. The leek is also more adaptable because it has greater cold-resistance
than the onion. Like onion, however, the leek is induced to bolt by low winter
temperatures; as bolting plants are not desirable for market, prolonged periods of low
temperature markedly affect planting dates and production periods. According to
Decoteau (2000) leeks will grow in any region that can produce onions and tend to
be more frost and freeze tolerant than onions. The tendency of leeks to bulb is an
undesirable characteristic that appears to be temperature controlled (with bulbing
occurring between 18–20 ∞C).
22.3.3 Soils
Leek is grown on practically all soil types, the most important requirement being a
loose texture. On peat soil, yields are usually high but quality is poor. Sandy clay
soils are most suitable for leek cultivation. Harvesting is difficult in heavy soils in
autumn and winter. Deep ploughing is a prerequisite for the development of long
white shafts. In the Netherlands it is found that phreatic water levels of 40 cm or less
below the soil surface result in poor yields; optimal levels are 80 to 90 cm. Randy
Baker (1991) reported that leeks may be grown successfully on a wide range of soil
types but deep top soil is preferred for vigorous plant growth and above average
yields. Soil pH 6.5–7.0 is most desirable. Coarse sands should be avoided because
sand particles under the leaf sheaths are not palatable to the consumer. The soil
should be prepared with green manure ploughdown or farmyard manure to enhance
organic content and provide nutrients and extra moisture-holding ability for the crop.
22.3.4 Season of sowing/planting
The objective in leek culture is the production of shoots of marketable size before the
leek plants bolt. In temperate Europe, premature bolting may be a problem of very
early plantings and normal bolting occurs in late-spring-harvested crops. In most