Leeks - SARE

Allium porrum (Alliaceae or onion family)

Production

Soil preparation

Apply compost and other amendments based on the results of a soil test.
Spread lime as needed to increase both the pH and Ca levels. Dolomite lime will also increase Mg levels. Spread gypsum when calcium levels are low but pH is correct.
A fertilizer company can add OMRI-listed potassium sulfate to compost if it doesn’t have enough K to meet the crop’s needs. If this isn’t possible, spread the correct amount of fertilizer and incorporate it before planting. Alternatively, you can side-dress it during cultivation. Divide the recommended rate of the soil test in half if side-dressing.
Most vegetable crops remove little P, but at times your soil test result will call for additional P. Unfortunately, there aren’t short-term options for an organic grower to increase the available P levels in the soil. Through the use of animal-based fertilizers, P will build up to a level in the soil that is sufficient for all vegetable crops.
Incorporate compost and plant leeks in raised beds.

Common recommended fertilizer rates¹

Nitrogen	Phosphorus	Potassium	pH
120	0-200	0-200	6.0-6.4
¹Rates are for New York and are from Cornell University’s Nutrient Guidelines for Commercial Vegetable Production (2019). Check the Cornell website for updated guidelines, or consult with local experts for recommended rates outside New York.

Varieties

New York variety trial: This 2020 report showed that Lancia and Skater are good early performers. Chinook, Defender and Tadorna were good performers in the late fall. Generally, there was more discrepancy between the early and later varieties, and while Megaton is generally held as the gold standard, it was a middle of the road variety in the trials.

Greenhouse guidelines

Start leeks in strip trays at a rate of 200–300 seeds per tray. Since leeks are started early in the season, germinate seeds in a germination chamber unless you can keep the greenhouse warm both day and night. Germination improves greatly at optimum temperatures.
When the leeks have a few leaves, repot them into a 1020 tray that’s well filled with a compost-based potting soil mix at a rate of 150 plants per tray.
Place plug trays on a wire mesh bench to encourage air pruning.

Signs to watch for and what to do

If necessary, feed with an OMRI-listed liquid fertilizer.
Leeks are slow growers and it takes a few months before they can be transplanted in the field.
Water carefully. Algae might form over time if the plants are too wet, and potassium and nitrogen will leach out.

Transplant readiness indicators

Pencil thickness is desired but not always attainable. Transplant in late May to July.

Transplant tips

Mix Streptomyces lydicus (as in the product Actinovate SP) and/or an extract of giant knotweed (as in the product Regalia) in a water solution and drench the complete tray before transplanting to prevent many soil- and foliar-borne pathogens, and to build immunity against them. Wear protective clothing and gloves when handling these products.

Transplanting in 5- or 6- foot raised beds

Rows	In-row spacing	Planting depth (inches)	Notes
2	5-9 inches	Plant deep, with just 1–2 inches of leaves remaining above the soil.	When leeks are pencil thickness, planting is usually done by hand. Punch a 1-inch hole 6 inches deep and place the leek in the hole. Ensure that roots aren’t bent upwards.

Cultivation procedures

Leeks are very sensitive to damage from aggressive cultivation. Take great care when cultivating leeks to avoid damage to leaves.
Use sweeps (with torsions if possible) followed by a finger weeder 7–10 days after transplanting, or as soon as possible without damaging the plants. Alternatively, use a tine weeder.
Hand hoe or hand weed between plants as necessary.
Use a finger weeder in combination with side knives or sweeps for a second pass. Alternatively, to obtain slight hilling, use spring hoes in combination with side knives. Both methods effectively eliminate small weeds.
If a third cultivation is possible, use hilling discs and hill up without damaging the plants.

Frost, disease and insect protection

Watch for onion thrips, and control with a spinosyn-based product, such as Entrust, or Beauveria bassiana, as in the product Mycotrol ESO. With Beauveria bassiana you’ll see results after a week of applying. Alternatively, use a mineral oil like JMS Stylet-Oil. Repeat applications of the selected product every 5–7 days. Don’t exceed the maximum rate of 3 applications per season for Entrust. As direct contact with the pest is required for all these products, only spray at night, as thrips are nocturnal. Act when pest pressure is still low.
Check for allium leaf miners. As this pest will emerge over several generations, follow local Extension guidance on when to use exclusion netting to avoid an infestation.
Purple blotch (Alternaria porri) occurs mostly in the summer under wet and humid conditions. Plants that are weakened by thrips are more susceptible to this disease. Keeping the crop weed free to allow for air circulation, planting long rotations, practicing good sanitation (e.g., removing or incorporating diseased plant material) and avoiding excessive N are good preventive measures.

Other cultural practices

Irrigate frequently for optimum yield and plant health. Frequency depends on soil type, evaporation, precipitation and the particular needs of the crop.

Cover cropping and/or double cropping

Work under any harvest remains to avoid insect or pathogen buildup, and plant a cover crop. In the northern United States and Canada, you can follow summer- and early-fall-harvested leeks with a cover crop of oats and peas in September, or rye and vetch planted at later dates. Adjust accordingly in other regions.

Harvest

Yield	An average yield is between 0.8–1 bunch per row foot (with 3 leeks per bunch), at a population of 36x7 inches.
Standards	Harvesting¹ 25 bunches per person, per hour
Standards	Washing It depends on where the roots are cut, but when roots are almost cut off, a minimum of 100 bunches per person, per hour. Leaving a short “haircut” of roots reduces washing efficiency but increases appeal to customers.
Tools and supplies needed	Knives, regular 1 ⅓-bushel boxes, extra boxes to use as a cutting surface for excess leaves, and either hand forks or a tractor with a bedlifter
¹Harvest rates don't include the time required to transport crops from the field to a wash and pack shed or storage facility.

Ready-to-harvest and quality indicators

Leeks are about 1 inch in diameter, with tall, dark green leaves that are free from blemishes and diseases.

Harvest and cleaning procedures

Wash hands and sanitize knives before harvesting.
Use different boxes in the field from the ones you use for distribution.
Leeks are much easier to harvest if you use a bedlifter first. Otherwise, you need to fork the leeks loose. The crew’s tasks are:
- One person loosens the leeks, either with a bedlifter or fork.
- A second person pulls the leeks and lays them out in rows with the roots facing the same direction.
- A third person cuts the roots off, at the place where the roots meet the stem. Don’t cut into the plant.
- A fourth person cleans off any old, diseased or damaged leaves by peeling them from the bottom.
- A fifth person trims off the tops by cutting across the leaves at the same height. Do the trimming with an upside down box as the cutting surface. Using a box as a cutting surface also helps to ensure that the leeks are cut the same length as the box.
If bunching the leeks, select 2–4 leeks per bunch that combined make for a uniform bunch.

Washing procedures

Wash hands and rinse boots before entering the wash-and-pack shed, and cover up field clothes with a bib. If a long-sleeve shirt contains soil, remove this as well.
Place leeks on a wire mesh table and rinse them off with a hose, or alternatively run them through a rinse conveyor washer. Add a sanitizer like hydrogen peroxide and peracetic acid to the water in the circulation tank of the rinse conveyor vegetable washer. Use the guide How to Wash Produce Using a Peracetic Acid Solution to establish how much sanitizer solution to add to water. Make sure you use the appropriate pressure on the nozzles to avoid crop damage.

Additional resources

Production Guide for Storage of Organic Fruits and Vegetables

Packing and storage summary for leeks

Cleaning in the field	Cut off roots and remove outer leaves.
Packing in the field	20 bunches per regular 1 ¾ plastic bushel box
Packing for delivery	11 lbs. per regular 1 ⅑-bushel box for wholesale Bunches or by the piece for a CSA or farmers market See the International Federation for Produce Standards for the correct PLU code. Add the prefix 9 for organic crops.
Storage	At 32°–41° and 95–100% humidity. Pack with ice in the bins for storage that lasts longer than a week. Leeks are slightly sensitive to ethylene exposure. Long-term exposure will turn green leaves yellow. Allow for good air exchange and don’t store with crops that release ethylene.

This material is based upon work that is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture through the Sustainable Agriculture Research and Education (SARE) program. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and should not be construed to represent any official USDA or U.S. Government determination or policy.