Growing Onion In Containers, Pots, Backyards

Growing Onion in Containers:

The following Information is all about Growing Onion in Containers.

Introduction To Growing Onions

the onion is also known as the bulb onion or common onion. Onions are a more widely cultivated vegetables.  Onions are perennial, annual plant and harvested in their first growing season. The onion plant has hollow, bluish leaves with a bulb at the base of the plant, bulbs swell day by day. The onion bulbs are compressed with stems surrounded by leaves that envelop a central bud at the tip of the stem. Onions have white-purplish flowers with many small buds. When the onion gets ready for harvesting, the foliage dies down and the outer layer of the onion bulb gets dry and brittle.  After harvesting the onions are dried and used for cooking. The onions have a yellowish-  to bluish-green color and they grow alternately.  The leaves die back in autumn and spring, the crop is generally harvested in autumn, if not harvested and left in the soil over winter, the growing point in the middle of the bulb begins to develop with new leaves in the spring. The plant generally grows up to 15 to 45 cm, the size of the bulb varies from 2-3 mm to 8-10 mm depending on the varieties.

Onion is one of the best container-grown vegetables, and many varieties of onions are available, and all types of onions thrive under the same growing conditions.

  • Scientific Name for Onions: Allium cepa.
  • Family: Onions belong to the family of Amaryllidaceae.
  • Common Names: Onions, Red onions, etc.

Varieties of Onions for Growing Onion in Containers:

Onions come in many different shapes, sizes, and colors.  Some of the popular cultivars are Red, White, yellow, and Spanish onions.

  • Yellow or brown Onions: These onions full-flavored and are the best choice for everyday use.
  • Red Onions: These are also called purple onions and are the best choice for fresh use.
  • White Onions: These are traditional onions used in Mexican dishes.

Onions are consumed at all immature stages; Large and mature onions are most eaten. Young plants are harvested before the buds appear and are called spring onions or green onions. The young bulbs before maturing are called summer onions.  Select the desired variety that suits your growing environment, check with the local growers to select the suitable variety.

the daily requirements of onions are classified into short-day and long days. Depending on their growing conditions, some onions required a short day, and some prefer long days.

  • Short-day onions need 10-12 hours of daylight in the summer to form onion bulbs. These are suitable for the warm climate; Short-day onions are suitable for southern parts of the country.
  • And long-day onions take 14-15 hours of sunlight in the summer to form onion bulbs. And long-day is suitable for the northern part of the country.
  • Intermediate varieties of onions: these onions need 12-14 hours of sunlight, they grow in neutral-day temperatures. Grown in the middle parts of the
  • All varieties of onions are suitable for growing in containers both outdoors and indoors. Onions are easily grown indoors under a grow light with timers. Green onion is the most suitable variety for container gardening.

Suitable Container’s for Growing Onion in Containers:

Growing Onion In Containers.
Growing Onion In Containers.
  • Onion grows under the soil, so for growing onion in the container, the depth of the container plays a major role.
  • Each onion plant required a minimum of 4-5 inches of space to grow.
  • The container should be capable of holding a minimum of 4-5 gallons of potting soil.
  • The ideal size of the container should be 10-14 inches in depth and 8-10 inches in diameter.
  • Select some large plastic container or planter boxes with a good draining system. Each container should have a minimum of 2 to 3 drain holes.
  • Some people use wide plastic tubs to grow onions, even grown in grow bags or some use plastic buckets, wooden boxes, or water tins. Prepare them with 2 to 3 drain holes.

The Best Season for Growing Onion in Containers:

  • Onion is a cool-season crop, so it should be planted in cool seasons.
  • The ideal season to grow onion in containers is a few weeks before the last frost date of the season. And these onions can be harvested in early summers.
  • Onions grow well in USDA zone 5 to 9.

A Suitable Location for Growing Onion in Containers:

  • Onion plants love sunlight, it grows well in bright light.
  • Sunlight requirement depends on the variety of onions you choose to grow, some need direct and the sun grows in partial shade. If growing from onions from seeds, check the requirement on the seed cover. If growing from sets, check with a local grower to know about the plant’s sunlight requirements.
  • Place the onion containers in a location where it receives 5 to 6 hours of direct sun per day.
  • Location for your container can be patios, balconies, terrace gardens, back yards, front yards, and outdoor gardens.
  • If growing onions indoors, onion seeds need a cool temperature to germinate and high temperatures for bulb formation. So, by the time the plant starts forming bulbs move the container to outdoor or place them near a windowsill where it can get 6-7 hours of direct sun.

Read this: Growing Chillies In Pots.

Soil Requirement for Growing Onion in Containers:

  • Onion thrives well in Loamy, well-drained, fertile soils. And the pH level of the soil should be between 6.0 to 7.5.
  • Onion plants do best with good quality potting soils, instead of gardening soil. Select the potting soil rich in organic matter and slightly alkaline. Select the potting soil that has equal quantities of peat and vermiculite or perlite.
  • Enrich the potting soil with compost or slow-release organic fertilizer for a good start of the onion plant.
  • Onions are the heavy feeder, soil should be enriched with nutrients throughout the growing season.

Propagating Methods for Growing Onion in Containers:

Onions are propagated from seeds, sets, or onion transplants. People living in long and warm growing seasons, propagate onions in containers from seeds. Onion plants from seeds take 8 to 9 months for harvesting. An Ideal method for propagating onions is through onion sets or transplants. Growing onions from transplants have a very short growing period and onions can be collected on short notice, but propagating onions from sets is highly recommended as they are less prone to diseases.

Growing Onion in Containers from Seeds: 

  • Select good quality seed from a reputed nursery or garden stores. The growing requirement of the onion should match our climatic conditions. Choose the seeds reading labeled requirements on the seeds covers or consult local grower on selecting seeds.
  • Use seed starting mix and seedling tray or small containers for planting seeds. Fill the pre-moisten seed start mix in the desired container and sow the seeds ½ deep and cover the soil loosely. And cover the seeds with a plastic cover or humidity dome and place seeds in a cool dry location
  • The ideal temperature for onion seed germination should be ranging from 21°C to 24°C.
  • Once the seeds sprout, remove the cover and place the container in a cool location with bright light
  • Keep the moisture levels of the soil constantly. Feed the seeds with fish emulsion or compost tea every two weeks.
  • And the onion seeds take 3 to 4 months to mature.
  • And transplant the seedling to the desired container outdoors when they are about 3-4 inches in height.
  • The Seedling should be hardened off before transplanting outdoor. Hardening Off is the process of making seedling adaptable to outdoor climates gradually. Expose seedling gradually to direct sun, cool nights, and to fewer water frequencies. Hardening off should be done in a sheltered location for a few hours on day one and increases the exposure day by day.

Read this: Growing Capsicum In Containers.

Growing Onion in Containers from Transplants:

  • Sowing seeds and then transplanting seedlings is a time taking process. Instead of sowing seeds and growing transplants, buy the transplants from nurseries and plant them in desired containers.
  • Growing onions from transplants have a very less harvesting period than from seeds.
  • Buy the transplants from a reputed supplier and transplants should be firm and dry to the touch.
  • Transplants should be planted 4 weeks before the last frost date.
  • Fill the desired container with potting mix, enriched with compost or slow-release fertilizer. And maintain soil temperature at 12 to 13°C before planting.
  • Plant the transplants 2 to 3 inches deep and 1 to 2 inches apart. Water the plant and place them in sunlight for 5 to 6 hours per day.
  • Maintain constant moisture levels and once the plant gets firm, add some organic mulch like dried leaves or straw to control weeds and retain moisture in the soil.
  • Use watering cans with a fine hose and water only at the base of the plant.
  • Overhead watering makes foliage wet and leads to fungal diseases.
  • Onions propagated from transplants take 5 to 6 weeks to produce onions.

Propagation for Growing Onion in Containers from Sets or Bulbs:

  • Onions can be easily grown from seeds and transplants, but growing onions from sets or bulbs are very easy and diseases resistant. Onion bulbs or sets come in many varieties, but they are sold by color not the variety.  Choose the desired bulbs or sets based on color. These are available in all nurseries and garden centers or farmer stores.
  • The Ideal time to plant the onions, bulbs, or sets in early spring or in autumn.
  • Fill the desired container with a good quality potting mix, enriched with slow-release organic fertilizer or compost. Slightly wet the moist the potting soil, before filling it into the containers.
  • Leave a ½ inch space between the rim of the container and the surface of the soil.
  • Push the bulbs about 1 inch deep into the soil with points facing upward. Maintain 2-inch space between each bulb.
  • Water the onion bulb and place them in sunlight for 6 to 7 hours per day. Check the moisture levels regularly as the potting soil dries out quickly.
  • Once the bulbs sprout with plants and grow up to 2 inches in height, place a thin layer of organic mulch to retain the moisture levels of the soil and control the weeds.
  • Feed the onion bulbs after 2 to 4 weeks of planting. And feed them every two weeks. Use a balanced organic liquid fertilizer in a ratio (8:8: 8 or 10:10:10). Mix the fertilizer with water in a ratio of 2 teaspoons of fertilizer for one gallon of water.

Watering Requirements for Growing Onion in Containers:

  • Onion growing in containers needs more water, as the potting soil dries out quickly.
  • If you are using ceramic containers, onions grown in these pots need more water frequencies.
  • Soil should be kept moist constant, as soon as it dries out, water it through till water floods out of the draining holes.
  • Water when the topsoil up to 2 inches deep dry. Water the plants checking moisture levels.
  • Onion plants propagated from transplants need more water than the plants propagated from sets.
  • Water the soil with a hose and nozzle, drip irrigation, or soaker hoses to keep the soil moist constantly.
  • Mulching is compulsory to retain the moisture levels in the soil.

Fertilizing for Growing Onion in Containers:

  • Onions are good feeders; fertilizing levels can be reduced if using a nutrient-rich potting mix.
  • During the growing seasons, onions should be fertilized with balance organic liquid fertilizers every two weeks.
  • Fish emulsion or compost tea should be used occasionally, this helps the growth of healthy leaves.
  • Don’t use a fertilizer with high nitrogen levels, high nitrogen levels can produce poor onion bulbs.
  • Too much fertilizer will burn the root and makes leaves yellow.

Pests and Diseases in Growing Onion in Containers:

  • Common pests that attack onion plants are thrips and onion maggots. Thrips mainly attacked during hot and dry weather. Spreading aluminum foil as mulch can control thrips.
  • These common pests can be treated with mild insecticide soap spray or Neem oil spray.
  • Onion bulbs can be attacked by adult flies, placing a thin layer of sand around the onion bulbs can control adult flies.
  • Diseases that attack onions are smut, downy mildew, and pink root due to fungal infections.
  • Using organic fungicides can control all fungal diseases.
  • Using good quality potting soil and healthy onion bulbs can control fungal diseases.

Read: Frequently Asked Questions About Plant Diseases

Harvesting Methods of Growing Onion in Containers:

  • Harvesting Onion Bulbs: when the tops turn yellow and start to fall, it indicates that onion bulbs begin to ripen. At that time, bend the top down to fasten the ripening process. Once the tops turn completely brown pick up the onion bulbs.
  • Harvesting green onions: pick up the green tops, when the top reaches up to 6 to 8 inches for green onions. Green onion is also called spring onions and they have a great taste when they are young and tender.
  • After harvesting, pull up the onions and leaves, dry them for a couple of weeks.
  • Store them in a cool and dry place, fresh onion has good taste and onion can store more than a year in room temperature.

Tips for Growing Onion in Containers:

Onion Growing Tips.
Onion Growing Tips.
  • Cover the onion plants with a floating row cover cloth to protect the plants from pests.
  • The size of the mature onion depends upon the healthy greens, the more the healthy leaves more the quality of the onions.
  • Onion plants are heavy feeders, feed the plants constantly with a mild liquid fertilizer throughout the growing season for the best results.
  • During the rainy seasons, move the onion container indoors or cover them up with garden cloches, plastic cover with good ventilation.
  • For sweeter onions, water the plants more than normal water levels.
  • Bolting in Onions: when the onion plant prematurely sends a stalk of flowers, stalks are called bolting. Onion bolting is caused when the plant is under stress. Other reasons for bolting are due to the hot, dry weather of summer.  As soon as you see onion bits, just snip the buds and then harvest and eat those onions first.

Post Harvesting Tips for Onions:

once the tops of the onion plant start to fall over, stop watering. An onion without water will start to harden. These onions are good for long-term storage.

In case if you are interested in this: Hydroponic Nutrient Chart.


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