Onions are absolutely indispensable to cooking. They add character to everything from pasta to pizza, and they can contribute a nice flavor to cooked vegetables such as green beans, too. Red onions taste great on salads. For the ultimate onion-eating experience, however, chop or slice an onion and use it to top a hamburger. Add a slice of tomato to that and the meal is complete. Delicious!
- Long growing season, if you are raising onions from seed.
- Loose, well-drained soil.
- Soil pH between 5.5 and 6.5.
- Chamomile. Said to improve growth and flavor.
- Pigweed. Pulls nutrients up from the subsoil, which benefits onions.
- Sow thistle. Believed to improve growth and overall health.
- Summer savory. Said to improve growth and flavor.
Marigolds are not good companions for onions, as they seem to attract pests in scientific studies.
Early in the season, you will need to decide if you are going to start your onions from seed or from sets. Seeds are much cheaper, but they tend to be delicate at first, and you will have to wait until the next year to harvest your onions. If you are feeling ambitious, give it a try. Beginners are better off planting sets.
To Start Seeds
- Plant seeds indoors 8 to 12 weeks before the last spring frost. In Kansas, sometime in February is probably best.
- Just barely cover the seeds in light potting soil
- Keep the seeds warm (70°F) until sprouted.
- Remember to harden off your seedlings by setting them outside for increasing amounts of time beginning about two weeks prior to transplanting.
- Immediately before transplanting, shake most of the soil off of the onions.
- Use scissors to cut the tops and roots back to two inches each.
To Transplant Seedlings or Plant Sets
- Till the soil thoroughly, removing all rocks, roots, and dirt clods while you’re at it.
- Rake the soil until the surface is fine and smooth.
- Plant onions outdoors about four weeks before the last spring frost, erring on the side of being a little early. In Kansas, late March through mid-April should do.
- Poke a hole in the soil for the seedling or set with your finger, making it roughly two inches deep.
- Insert one seedling or set into each hole (sets go in pointed side up) and gently pack the soil around it.
- Plant onions three to four inches apart. Be sure to leave some walking space between rows.
- Lightly mulch the onions.
- Keep them watered until they sprout.
Onions, like other root crops, suffer in soggy ground. Do not overwater them. Some mulch is beneficial, but keep it fairly light until dry weather sets in. By the same token, keep up with the weeds. A thick growth of grass tends to hold in moisture, which can lead to rot.
As the season progresses, keep a close eye on your onions. As the tops start to fall over and dry out a little, stop watering the plants. When most of the tops have fallen, bend down the rest with your hand to encourage them to start drying.
Pests and Diseases
- Botrytis bulb rot.
- Neck rot.
- Onion smut.
Any time you see onions with tops that are completely dry, pull them immediately. Let them dry on an elevated chicken wire screen in the shade, preferably in a breezy spot, for several days. When the tops feel completely dry and papery, brush off all of the dirt and loose skin and bring the onions inside.
Only store cured onions, and do not attempt to store any that seem likely to rot. The surest way to store onions is to braid them together or put them in a mesh bag and hang them up in a dry area just slightly above freezing. Another method is to loosely pile them into a slat-sided box. Be sure to check on them frequently, and remove any onions that are rotting or sprouting. (If you raised your onions from seed, remember to replant them in the spring, just as you would sets.)
Be aware that some onions simply will not store well. These are usually the ones that received too much water during the second half of the growing season. They will have thick, soft tops, possibly with a little green still in them. Use them as quickly as possible. If you must store them, your best bet is to chop them up and freeze them in plastic bags. They will have quite a bit of extra moisture when thawed, but once drained they are still good for cooking.
- Harvest and cure normally after the first growing season.
- Braid the onions and store between 32°F and 45°F. (Oddly enough, 77°F to 95°F will also work.)
- Replant the onions normally in the spring.
- Separate varieties by one to three miles, if possible.
- If you can’t separate varieties, bag the tops before flowering to avoid cross-pollination.
- Pollinate flowers in early morning or late evening to avoid insect interference.
- Remove the bags from the flowers and use a fine paintbrush to distribute pollen between them.
- Replace the bags as quickly as possible.
- Allow the seeds to ripen and dry on the plants, but be prepared to harvest them early if rain threatens.
- Bend the seed head over, still in its bag, and cut it from the plant.
- Store seed heads away from direct sunlight to finish drying.
- Thresh the seed by crumbling the seed head or stomping on the bags.
- Screen the seeds to remove debris. You can also winnow them by pouring them from bucket to bucket, but only if the wind is light.
- Store in a cool, dry, dark place. Onion seeds only last a year or two.
Onion Disease Guide
Free PDF with plenty of concise and well-photographed information on identifying onion diseases.
A list of factsheets.