Leek Soil Requirements, Soil Preparation, and Planting of Leek

Leek Soil Requirement and Site Selection

While soil is not usually a restrictive factor for leek growth, the plants thrive and produce larger, high-quality shanks when the topsoil is relatively deep, has good drainage, high organic-matter content, and a neutral pH ideally 6.5-7 (6-8 is also acceptable). If the pH is lower than the optimum, the farmer may consider applying a light dressing of lime or dolomite (incorporate 3-4 tons per hectare 1-2 months before planting). Heavy soils (over 30% clay) should be avoided for different reasons. In the first case, there is a high risk of forming crust, which will have a negative impact on the growth of the leek shanks. In the second case, the sand particles may penetrate among the leaf sheaths making it difficult to be cleaned (not desirable by the consumers). Finally, you can choose to plant them in a sunny location to boost plant growth.

Leek seeds need a 20 °C (70 °F) soil temperature to germinate and most crops start in early spring when the environmental conditions are still unfavorable. Thus, many farmers start their crops by sowing the seeds in small pots-trays in a greenhouse and then transplant them to their final position in the open field. If this is not possible, the farmer can purchase the leek seedlings (transplants) from a legitimate plant nursery and plant them directly to the ground when needed.

How to prepare the soil for sowing and planting the leeks

The basic soil preparation starts a few months before planting leeks. Farmers plow well at that time, up to 40 cm depth. Plowing improves soil aeration and drainage. At the same time, plowing removes rocks and other undesirable materials from the soil. This step is important since leeks need loose soils for shank growth and enlargement. Additionally, these cultivation practices (e.g., plowing, tillage, etc.) are essential for eliminating the weeds and preparing a clean seedbed for the leeks. Weeding should be repeated right before planting and continue during the first 2 months of leek growth since leeks are inferior competitors and will quickly be drawn by weeds (if left uncontrolled).

A few weeks before planting, many farmers apply a pre-planting fertilizer such as well-rotted manure (around 10 tons per hectare or 4 tons per acre) or synthetic commercial fertilizer, always after consulting a local licensed agronomist. Avoid using organic animal products too close to planting because they may attract the corn seed fly (the larvae are destructive to the seeds). Most farmers integrate base dressing on the same day (into bands), using tillage tractors. In most cases, leeks are planted on raised beds of 1m width, formed by tractors a few days before planting.

If drip or micro-sprinkle irrigation is applied to the leek crop, then the farmer should install all the equipment needed (irrigation pipes) before planting the plants. Following the installation, some leek growers can apply soil disinfection substances through the irrigation system in case soil analysis has revealed soil infection problems (ask a licensed agronomist in your area). Depending on the rainfalls, it is important to keep the soil moisture with daily irrigation during the first 4 days after sowing.

The next step is optional; it is mainly used in countries with non-optimum soil temperatures during planting and is the linear polyethylene coating. Some leek farmers cover the rows with black or green Infrared – Transmitting (IRT) or black plastic film. They use this technique to maintain the root zone temperature at optimum levels and prevent weeds from growing.

Leek Planting and Plant Distances

As mentioned above, there are two main ways to start a leek crop:

By seed (directly sown on the field)
By seedlings – transplants (after they have been grown indoors in a greenhouse/nursery)

Each method has its advantages and drawbacks, which we will analyze in the following lines.

1.Starting a leek Farm by Seed

It is important to select healthy certified seeds from a legitimate seller to ensure the variety purity, health, and relatively high germination rate. Farmers usually have a larger variety of cultivars to choose from when starting from seed.

In small-scale farms, growers start their crop during spring, in most cases, by mixing leek seeds with sand to achieve a better spreading rate. On the other hand, growers in large commercial farms mainly use seeders, which sow the seeds in rows on raised beds. The most commonly used distances that most of them prefer are 25-40 cm (10-15.7 in) and max 60 cm (23.6 in) space between rows. Once the plants have reached an acceptable size, producers thin them to leave 15-20 cm (6-8 in) space between plants.

The quantity of the seed sowed depends on the variety of the leeks, planting distances, the germination rate, the seed size, the nature of the final product, and the producer’s yield goals. Leek seeds need a soil temperature of around 20-25 °C (70-77 °F) and around 7-15 days to germinate, depending on the weather conditions and the condition of the seeds. Leek producers have reported that they need 1.5-4 kg of leek seed per hectare.

2.Starting Leek Farm by Seedlings

This method is the most commonly preferred as it offers multiple benefits to the producer, despite the initial higher cost of the starting material. Leek produced by seedlings has a better volume and uniformity rate. Furthermore, producers can harvest yields earlier in the growing season.

In the case of seedling transplanting, producers begin by sowing leek seed in an indoors-protected environment. They start 4-8 weeks before the day of transplanting and the last spring kill-frost. The seeds are sowed in nursery beds or trays at 1 cm depth and a 10-15 cm distance between them. Different leek varieties are transplanted at different times of the year. By the time young leek seedlings are about 15-20 cm (6-8 in) tall and 1 cm (0.4 in) thick, it is time to transplant them to the open field. Before planting, plants, in most cases, are trimmed to 10 cm (4 in) height. Some producers trim the roots as well.

Producers plant the young leek seedlings inside furrows of a depth of 15-23 cm on raised beds (trenches). They keep, on average, 25-60 cm (10 in-24 in) between rows and 15-20 cm (6-8 in) space between plants in a row. Following this pattern, they plant approximately 120.000 to 500.000 plants per hectare. Summer varieties are generally planted at closer distances, while winter ones in larger distances. After 4 weeks, they may need to hill up the soil in order to cover the growing stems further. Since leeks are commercially exploited mainly for their edible shanks (pseudostems), they need to be white, and hilling (blanching by eating up) is essential to block contact with sunlight and, as a result, photosynthesis (and green color).

References

15 Interesting Facts about Leeks

Leek: Info, Facts, Nutritional Value & Health Benefits

Leek Plant Information and Variety Selection

How to Grow Leeks at Home

Commercial Leek Farming – How to Grow Leeks for Profit

Leek Soil Requirements, Soil Preparation, and Planting of Leek

Leek Water Requirements and Irrigation Systems

Leek Fertilization Requirements

Leek Harvest, Yields and Storage

Leek Pests, Diseases and Weed Control

Leek in Bulk Wholesale Prices

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