Perennials Onions and Leeks Provide a Supply of Edibles and Planting Stock Year After Year
Are you interested in creating a sustainable supply of onions, shallots, and leeks? Perennial onions (Allium cepa var. aggregatum) and perennial leeks (Allium ampeloprasum) are self-multiplying and over time have the ability to provide you a crop of green onions, onion bulbs, or leeks, in addition to planting stock for the following year. They belong to the Allium group, which includes onions, garlic, chives, and leeks. A perennial is a plant that can live for multiple years. They may complete their life cycle over two or more years. Many of these perennial alliums do not produce true seed, but instead propagate themselves vegetatively. Like garlic, you plant one bulb and it divides over a season, often winter and spring. The results when you dig them up: multiple bulbs which you can store, eat, or re-plant. Thus, your supply can be continuous and you will eventually grow enough so that you do not have to buy new bulbs to plant each year.
Multiplier onions, potato onions, and shallots multiply from one clove to form a bulb of several “cloves”, similar to garlic. Potato onions are yellow and shallots come in red, yellow, and grey. Similar to traditional bulb onions, we consume the bulb part. However, the bulbs of perennial onions and shallots are often smaller than the larger bulb onions. To plant, separate bulbs into individual cloves and plant with ½-1” soil above the bulbs. Reserve some for spring planting in case of a severe winter. A few inches of straw mulch provides winter protection and helps maintain soil moisture. If no mulch is applied, hill them with 2-5” soil. In spring, they will sprout green tops. Cut off the scapes, or flowering tops, as they form, to encourage bulb growth. Scrape away extra soil in early spring, and remove mulch approaching harvest. Then, dig them up to harvest in May-July, once the tops, or “necks”, begin to weaken at the base and fall over. This will help the skins harden appropriately for storage. Continue harvesting over a two-week period, digging each plant as the neck falls. Move them immediately to shade after harvest and allow to cure in a well-ventilated place. An ideal place is in a shed or storage room, laying flat on in a single layer on a screen. Some of the plants may have necks that remain green. Harvest these last but eat them first as they will not last in storage. Once they have cured for four to six weeks, cut off the tops and extra roots and store between 32 and 40 degrees F or 50 and 75 F in a well-ventilated space. If you store them between 40 and 50 degrees F they will initiate sprouts. Check on your stored onions periodically and remove any that are starting to go bad.
Walking onions are grown for the green tops, which are cut repeatedly as green onions. These produce bulblets at the top of the greens that fall over and sprout. The most popular variety are Egyptian walking onions.
Plant bulbs in fall and begin harvesting the greens when they sprout in spring. When the bulblets are produced at the top of the greens, their weight makes the green topple over so the bulblet can plant itself. The newly planted bulblet will sprout a new green, and the cycle continues. The bulblet needs to be at least partially covered with soil to plant itself, and sometimes benefits from a little “encouragement”. Walking onions can be left in the same place for a few years, but can be dug and moved if desired. They will likely need to be thinned and the bulbs separated every 1-3 years. You can also dig them to consume the strong-flavored bulbs. The bulbs are especially good for pickling.
Perennial leeks are slender, bunching leeks that multiply into many small bulbs. Plant the dormant bulbs in spring. Harvest green shoots as they emerge in fall or winter. Or, leave them to mature late winter and eat the slender new leeks in spring. The greens will go dormant in summer and then resprout as the season cools. Dig these and divide every few years. These may flower and form true seed every few years. However, it takes two years to grow a harvestable product when starting from seed, so dividing the bulbs expedites the harvest.
Choose a well-drained soil rich in organic matter for your perennial onions and leeks. It is important to start in a well-amended bed prior to planting a crop that will be in the same place for several years. A raised bed filled with a compost-based media is ideal. Make it no wider than twice as far as you can reach- 4’ is often a good width for raised beds. If it is a new area or one you have not tested in several years, take a soil test and correct soil pH and nutrients according to test results prior to planting. Avoid planting into beds that have had other alliums such as bulb onions or garlic in recent history. Keep beds weed-free and ensure that the plants get adequate moisture, but not over-watered. Straw mulch can help keep the beds moist, but should be removed as you approach bulb harvest.
If you are new to perennial onions, purchase a starter set this fall to try. As you harvest and divide them, you will build a self-sustaining supply of diverse alliums for your kitchen. With more questions about planting perennial onions and leeks, or with other gardening questions, contact the N.C. Cooperative Extension, Caldwell County Center at (828) 757-1290, Monday-Friday, 8 a.m. – 5 p.m. We have soil test kits available at the Extension Center, and they are free until the end of November.