Onions are a big subject. There are many. Since I already posted about garlic that subject is left from this discussion. But suffice it to say that garlic is an onion (Allium sativum). Leeks are onions too (Allium ampeloprasum var. porrum). Strangely enough, elephant garlic, also already mentioned in the garlic post, is also a leek (Allium ampeloprasum var. gigante). I will help you sort out the onions so you can have the information you need to purchase and grow the ones you want.
Bulb Onions, Dry Storage Onions
Let’s start off with the most challenging to grow. And don’t be intimidated. Growing bulb onions (Allium cepa) is not that hard, especially if you select the right varieties and plant them at the right time (we will talk about bunching onions and scallions later).
The easiest way to start bulb onions is to order sets or transplants and plant them in early spring into a full to part sun location–the earlier the better, so if you can protect them from frost, go as early as January. If you don’t protect them from frost, wait until March. Bulb sets look like tiny onion bulbs about the size of a dime if your source is good. The closer to being dime-sized the better. Bigger bulb sets are not better. Transplants are small onion plants with green tops, basically looking like scallions. They are a quick way to get started. When you get your transplants they will come in bundled sets. You will usually plant them and snip off the tops of the leaves. Starting from seed is the most challenging method, but if you master the timing (which means frost protection) you will have more varieties at your disposal to start. There is also something satisfying about starting onions from seed.
Onions start bulb formation according to how much daylight there is–different varieties of onions require different day lengths to initiate bulbing. Most common varieties belong to one of two sorts: long-day (for northern latitudes) and short-day (for southern latitudes). Short day onions really are best for us in Tucson. After that the variety choices are dependent on what you want.
Prepare a nice soil bed for onions with some manure, lots of compost and good drainage. After you plant onions, lay a nice layer of mulch down. Onions have very limited root systems so they don’t compete well with other plants. So keep greedy weeds out of the onion bed, but be careful not to damage onion bulbs. Most weeds pull up pretty easy especially if you get them young so avoid using tools that can bruise the bulbs. Other than this, or maybe an occasional feeding of fish emulsion or compost tea or kelp, there really isn’t much you need to do. Onions do best when left alone.
Lettuces and other plants that can protect onions from the brutal warm season sun are good to plant so that bases of onions are shaded. Do NOT plant them with peas, beans, asparagus or sage. For green onions, plant close together. For true bulbs, plant about 6 inches apart (there will be differences in onion sizes so follow the directions of the variety you have chosen which may suggest tighter or looser plantings).
Onions should be harvested when about two-thirds of the tops have fallen over. They should be left out to dry on a screen or dry, shady location for about a week. Different onions have different storage capacity, so pay attention to what is said about the varieties you have selected. I always try to have some longer storing varieties, but also have some interesting fun but short lasting varieties as well. Plan accordingly how you can preserve your crop (jarring/pickling, drying, etc), or plan on trading with friends.
Another point: scallions are indeed just green onions, or bulb onions that have not made bulbs yet. But there are specific varieties that are true scallions and are much tastier and sweeter than just any old onion. If you want scallions, pick a variety listed as a scallion variety.
Multiplier onions, or potato onions are related to bulb onions. They have a shallot-like flavor. They are easy to grow and ideal for hot, dry climates. To grow them, separate bulbs, and plant in the fall 1 inch below surface and 12 inches apart. Bulbs will multiply into clumps and can be harvested throughout the cooler months. Tops will die back in the heat of summer and may return with monsoon rains; bulbs can remain in the ground or be harvested and stored in a cool dry place for planting in the fall. The plants rarely flower; propagation is by division. This is an old fashioned variety that should make a comeback.
Territorial has multiplier onions.
Often found in the herb section of the nursery, chives are onions. But they are a wild type used mostly for their greens as a raw spice. Plant sets or potted plants in fall. Easy to grow, feed occasionally. Divide when they get crowded. Garlic chives are discussed below, and actually a different species. Chives have gorgeous flowers too.
Territorial has chives as plants and sets.
Allium ampeloprasum var.porrum
Leeks are best started from seed indoors in February or so (about 4 weeks before last frost date). When there is no threat of frost transplant them in full to part sun (they should have the girth of a pencil). Space them 6-7 inches apart. They like a little more food than onions. Fish emulsion is great. Compost tea, kelp, side dressings of compost…you know, what I always say. Short season leeks are harvested usually in summer, late season in the late summer early fall. Don’t plant with peas or beans.
Territorial has seed and plants, including a quick variety called Roxton.
Ramps, Wild Leeks
Allium tricoccum, A. burdickii
These plants have the pleasant taste of sweet spring onions with a strong garlic-like aroma. Plant in rich soil with a thick layer of compost.
Ramp Farm is one place to find both bulb and seed.
Allium cepa var. ascalomicum
Shallots can be confused often with multiplier onions and top setting onions whose bulbs look similar. True shallots have a delicate flavor, especially favored in French cuisine. Grow them as you would garlic, plant in October. There is another species, Allium kurrat, also known as Egyptian Leek. I have not grown this but want to give it a try.
Kitchen Garden Seeds has seed and sets of leeks.
Egyptian Walking Onion
These are cool plants, easy to grow. They even plant themselves by falling over and leaving their top set onions on the ground to root. Plant them in nice soil in spring and let them do their thing.
Bulblets are available at Territorial.
Chinese Chives, or Chinese Leeks
Plant from seed in spring and let multiply. Will live for several years especially if you keep divided. This is an important onion in asian food used in almost all stir frys and even to season woks. They look like flattened chives.
Asian Bunching Onion
These are gorgeous plants, some with gorgeous coloring (like red Asian bunching onion). Start seeds indoors in late summer and set out with garlic. Protect from hard frosts. “Splitting types” are another very important variety used in asian cuisine. These are more cold-resistent. Asian bunching onions are mostly easy to grow and last a long time. With the exception of protecting some varieties from frost, and occasional feeding, these plants are care-free and delicious.
Kitazawa Seed is a great source for all kinds of asian vegetables and the best I know for asian onions. They separate onions from bunching onions and call chinese chives, chinese leeks.
This is another important Chinese wild bunching-type onion. Plant sets in fall. Plants do not produce seed. I have a hard time finding a source for Rakkyo, if you find one, let me know. [UPDATE: I have found Rakkyo onions at Seed Savers Echange. You will need to become a member to get bulbs of this multiplier onion, but it is worth it not just for the onions, but because Seed Savers promotes the worthy cause of maintaining a healthy supply of heirloom crops, preserving genetic diversity in our food supply NATURAL GENETIC DIVERSITY.]
Eventually I will probably address all these onions and more in detail. This article is meant mostly as an overview of the onions. I may have missed some things, let me know.