How to Grow Salsa in Pots – Onions

How to Grow Salsa in Pots – Onions

Onions (Allium cepa or A. cepa var. cepa) are daylight sensitive, and will not produce large bulbs if they do not get enough hours of daylight. Onions are categorized into three categories: short day, intermediate day, and long day. There is much overlap as to which varieties do well in each area, since the determining factor is whether or not there will be enough days in the growing season between freezes for the onions to mature. High temperatures also inhibit bulb formation. The further north you garden, the more daylight hours there are in a day during the summer.

  • Short-day onion varieties will bulb up with 9 to 10 hours of sunlight. Short-day onion varieties mature in about 110 days in the south and 75 days in the north. Short day onions do best when grown in the South during fall and winter.
  • Intermediate-day onion varieties require 12 to 13 hours of sunlight per day. Intermediate-day varieties are the most widely grown and adapted, and mature in about 100 days. They will produce good-sized bulbs when planted everywhere except south Texas or south Florida.
  • Long-day onion varieties require at least 15 hours per day of sunlight. Long-day onions do well in the Midwest to the Canadian border. If planted early, long-day onion varieties do well north of a line that runs from northern California to Virginia.

How to Grow Onions: from Seeds, Transplants, or Sets

There are three ways to start onions, from transplant, sets, or seeds. Transplants are baby plants that are available through your local nursery or by mail order in the spring and sometimes again in the late summer. Onion transplants or seeds can be planted out as soon as your soil can be worked in early spring, since they will not be harmed by frosts as long as the soil does not freeze.

Sets are tiny onions that have been grown closely together to prevent bulb formation. They are harvested at a specific time and stored so that they will be easy to plant and will mature quickly into larger onions. Starting with onion plants or onion sets is easier for a beginner than starting from seed.

The most time consuming method is to start onions from seed, and in most of the country this entails starting them in flats long before the last frost date in order to give the plants long enough to mature in containers or in the garden. For most areas, starting onions from seed during February and March is optimal. Starting onions from seed will produce the best quality onions which mature the quickest and store the best.

  • If you live in USDA plant hardiness zone 7 or warmer, short day onions are the best choice. ‘Grano’ and ‘Granix’ and the many cultivars of these, and ‘Texas SuperSweet’ and ‘Burgundy’ can be planted from seed in the fall or set out as transplants in January. Except in south Florida and south Texas, intermediate day bulbs will produce nice sized bulbs. ‘Red Creole’ is one of the best storage onions for the South.
  • If you live in USDA plant hardiness zone 5 or 6, intermediate day onions are a good choice. Short day varieties can be started indoors in the winter and transplanted in the spring.
  • If you live in USDA plant hardiness zone 6 and colder, you can grow long day varieties as well as sets for red, white, or yellow onions, and ‘Walla Walla Sweet Onion’ from seed. Short day onions will produce small bulbs in 75 days if planted in late spring in northern states. The earlier you plant, the larger the onions will get.
  • Gardeners in most zones will have success with ‘Giant Red Hamburger,’ ‘Evergreen Long White Bunching,’ and ‘Early Italian.’

The determining factor is whether there are enough warm days to grow a big bulb, given that the days are long enough to signal the bulb to respond to grow. Your local nursery will stock the correct varieties for planting in your area. Your local county extension agent is a free resource to answer questions about which varieties will do well in your location.

Few pest or diseases bother onions, although deer and rabbits like to eat the tops. Thrips are the most prevalent insect pest, causing the onion foliage to become silver. Thrips can be controlled with insecticidal soap. Thrips live on weeds and can be discouraged by keeping the onion bed weed free. Onions are a good companion plants to many plant varieties, but not to beans.

How to Plant Onions

Onions do best in rich organic soil that has compost or well-rotted manure added. A complete organic fertilizer which is high in phosphorous, such as 5-10-5, or bone meal, should be applied at planting time. High sulfur content in the soil or fertilizer will usually cause onions to be more pungent. Since onions have a shallow root system, try not to get fertilizer on the onions when you side dress with fertilizer during the season.

Sow onion seeds indoors 8 to 10 weeks before the last hard frost, or in the fall in frost free areas. Germination will take 1 to 2 weeks. When seedlings are 1 to 2 inches tall, thin to 3 inches apart. Sow seeds outdoors about 2 weeks before your last frost. For bunching onions which are used as scallions, plant seeds in spring and fall.

If you mail order plants or sets, open the box immediately and remove plants. Keep them cool and dry until planting time, and do not water them or put them in soil until then. Onion transplants should appear dry when they arrive, and they can live off of resources stored in the bulb for about three weeks.

Plant onions sets 4 to 6 weeks before the last spring freeze. Plant no deeper than 1 inch deep, since deeper planting will inhibit bulb growth. If you want to harvest green onions as well as large onions, plant onions twice as thick as the variety states and then harvest every other onion when the plants reach 6 to 8 inches tall.

Different varieties of onions grow to different sizes and some will need more space to mature, so thin according to the seed package instructions. Overcrowded onions will not grow to their potential size, and are more susceptible to disease and insect problems. Bulbs will usually push out of the soil as they expand, and there is no need to cover them with soil as they mature. Bulbs form almost entirely above ground, and should not be covered with mulch.

Water thoroughly after planting. Onions have shallow roots, and do not respond well to either under- or over-watering. The soil should be kept moist to the level of the bulb’s bottom until two weeks before maturity, at which point, stop watering. Leaves with a yellow tinge during the growing season signify over-watering. While onions are setting bulbs, they need ample moisture. Onions need more water closer to harvest time.

Early in the season, a layer of straw mulch will help to control weeds. This should be pushed back once the bulbs start to form so that they will cure properly. If onions try to set flowers, which is more common when starting onions from sets, most gardeners break the flowering stem since flowering will cause the bulb to stop growing.

Plants from the onion family should not be planted in the same place for at least two years to avoid spreading soil borne diseases and insects to the next crop of the Allium species. The Allium family includes chives, garlic, and leeks.

How to Grow Onions in Pots

Start seeds inside 8 to 10 weeks before your last frost under grow lights or in a brightly lit window. Grow lights help to get your plants off to an early, healthy start, and you can choose from a much wider variety of vegetable seeds by starting your own from seed inside.

If you want to grow onions in a container, space according to the variety and grow them in a pot that is at least ten inches deep. A wide container like a storage bin with holes in the bottom is ideal because you will be able to grow more onions. Use a soilless mix with added compost and an organic fertilizer which is low in phosphorous.

Plant onion seeds or onion sets to the depth recommended by the supplier. If you would like to harvest green onions, plant at half of the distance recommended and harvest every other onion in about a month.

Once the days warm up, you can move the container onions outside. Onions will not be killed by an overnight frost, so you can leave them outside unless there is a prolonged cold spell below freezing.

Water when the top inch of soil is dry to the touch. You may need to water every day during hot periods. Feed your onions every two to three weeks. Excess nitrogen will cause leafy growth at the expense of larger bulbs.

How to Harvest Onions

When onion tops start falling over, let the soil dry out so that you can harvest. At this point the plants should have over a dozen leaves. After about a quarter of the tops have turned yellow and fallen over, bend the tops over. After a few days, harvest the bulbs and leave them in the garden with the leaves pulled over the bulbs to prevent sunburn. Harvest onions early in the morning when it is expected to be sunny for a few days. Do not wash them or remove any layers of the papery wrap, just gently remove excess soil.

On dry days outside, this usually takes 2 to 3 days. If there will be no rain, leave them in the garden for up to a week, then move them inside to a warm, dry place and spread them out to receive good air circulation.

If it will rain, dry onions indoors in a well-ventilated room. Spread them out to give them room to breathe and allow 2 to 3 weeks for them to cure.

How to Store Onions

Sweet onions, as a rule, mature about a month sooner than varieties grown for storage, and will keep for one to four months. As a general rule, the less sweet the onion is, the better it will store. Use sweet onions first after harvest. Long-day onions are best for storage.

Onions must be cured in order to store without rotting. When you pinch the neck of the bulb, where the leaves and bulb meet, it should be dry and should not slide. Once they are dry, trim the roots and cut the tops to one inch, unless you are planning on braiding the tops. Store onions in the legs of re-purposed panty hose with a knot in between each bulb, or in mesh bags, in a cool, dry place. Onions store best at close to freezing, but not freezing, temperatures.

About Olympia


My name is Olympia Paz, and I am a graduate of Kansas State University.with extensive studies in soil science (agronomy), horticultural science, and biology. I have continued my own studies in these areas, especially soil science, and applied my knowledge to growing nutritious organic food in my home gardens, containers, and inside.

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