Solving the Mystery of Growing Onions

Grow Onions All Year, Even in Pots!

 

Onions are one of my favorite vegetables to grow all year round because I use them so much in cooking.  Green onions or onions that are harvested at maturity (when they have formed those nice round bulbs) add great flavor to almost any salad, side or main dish.  For years though, the onions I planted never formed nice round bulbs but just turned into fat green onions.  Then I heard about short day, long day and day neutral onions.  I had been planting the wrong type of onion for where I live!

What type of onion to plant?

Onions begin to form bulbs in response to day length.  Short day onions form bulbs when there are 10 to 12 hours of daylight, long day onions need 14 to 15 hours of daylight.  Day neutral onions form bulbs with 12-14 hours of daylight.  Which onion to plant depends on where you live.

• Short day onions should be planted south of San Francisco in California.  (For the rest of the country, south of a line drawn between San Francisco and Washington DC).  Varieties to try are Texas Super Sweet, Texas Early White, and Red Creole.
• Long day onions should be planted north of San Francisco where the summer daylight hours are longer than in the south.  Red Zeppelin, Walla Walla, and Sweet Spanish are examples of long day onions.
• Day neutral onions form bulbs in any area.  Candy, Super Star and Red Candy Apple are varieties to try.

When to plant onions

• Short day onions are often planted in southern regions in fall, but I also plant them in winter (Dec/Jan) in my southern California garden.  They grow through winter and spring and are ready to harvest in late spring/early summer.  The earlier you plant them, the larger the bulbs get.  You can plant from seed or buy bunches of already started plants (my favorite mail order source for plants is Dixondale Farms).  Seed of course takes longer to produce mature onions.  Short day onions can be planted in northern regions in spring, but the bulbs don’t get as large there.
• Long day onions are planted in northern regions in late winter/early spring.
• Day neutral onions produce bulbs in all regions.  They are planted in fall in southern regions and in the spring in northern regions.

How to plant onions

Onions can be planted in containers, raised beds, or directly in the ground.  In containers, use fresh potting soil.  In raised beds or in the ground, cultivate the soil at least 10″ deep and mix in compost and organic fertilizer (use fertilizer with nutrients that have higher phosphorous or middle number such as 4-6-4).  If planting in the ground, make raised furrows at least 4″ high and 20″ wide.  Plant two rows of onions in each raised furrow.

• Planting from seed:  make shallow furrow in the soil, space seeds about an inch apart and cover with 1/4″ of soil.  Keep soil moist until seed germinates, then water as necessary depending on weather.  When plants get to ‘green onion’ size (thick as a pencil), harvest so that remaining plants are 4″ apart so they have room to form bulbs.  Note that onions planted from seed can take up to 4 months to mature.
• Planting from transplants:  poke holes in soil 1″ deep and 2″ apart if you want to harvest every other one during the growing season or 4″ apart if you want them to grow to maturity.
• Planting from onion sets:  Onion sets are immature bulbs from the previous season about 1/2″ in diameter sold in bags.  Plant these the same as transplants.  Although onions grown from sets are less susceptible to disease, they are more prone to bolt (send up flower stalks) which interferes with the quality of the mature onion.
• Planting from six-packs:  At nurseries ‘bunching onions’ are sold in six packs.  The trouble is that the seedlings are usually growing so close together in each cell they can’t mature to even green onion size and it’s difficult to harvest one without pulling out the whole bunch.  So I like to space out individual seedlings by pulling out one cell of the six pack and gently pulling the seedlings apart.  Then I plant as above for ‘transplants’.

How to harvest and store

• When the tops turn yellow, bend them down so they are horizontal.  This sends the plant’s energy into the maturing bulb.
• When the tops turn brown, pull or dig up the onions and leave them laying on the soil in the sun until the outer skin is dry.
• Brush dirt off the onions, cut off tops and store in a mesh bag in a cool place.  They will keep for 4 months to up to a year.