The Incredible Onion - How to Plant Onions at Home

The Basics - Growing Onions

Onions, just like any other vegetable, have a range of health benefits. They can prevent and treat various diseases and repel certain bloodthirsty insects. Onions can treat asthma, the common cold, respiratory problems, coughs, bacterial infections and angina, among other diseases.

With regular use, onions can also prevent heart disorders, cancer and diabetes, among other life-threatening diseases. They can also boost your sexual drive, heal various skin conditions such as acne and help nourish your hair, among other benefits.

What is an Onion?

Also known as Allium cepa scientifically, an onion is a type of vegetable. Onions are rich in antioxidants to help fight free radicals in the body. They have been used for their medicinal values since time immemorial.

Available as bulbs, onions can be yellow, red or white. Spring onions are also known as scallions or green onions. Onions have a sharp, pungent flavor and strong taste. Despite being a temperate vegetable, onions do relatively well in tropical, temperate and subtropical climatic conditions.

Humans have cultivated and used onions in their diet as a staple plant for at least 7,000 years. Although you'll find some wild onion species in specific regions in Asia, onions are mostly cultivated and grown worldwide. Egyptians buried pharaohs with onions to help enrich their diet in the next world.

In 5000 BC, onions were already being used in China. The popularity of onions can be attributed to their medicinal values, high availability and versatility. Onions have antibacterial and anti-fungal properties, hence their use in treating fungal infections in households.

Why You Should Plant Onions at Home

Apart from the health benefits of using onions, there are many reasons why you should plant them at home. Onions do well in well-drained soil with sufficient moisture levels. Grow onions in your garden or backyard to gain the most from their range of benefits.

Onions are an integral part of preparing culinary and cuisines worldwide. You can also use them to cook your simple dishes at home. Since they are 'companion plants', you can easily grow onions beside your other plants and vegetables. They also do well in a wide range of climates.

According to the World Health Organization (WHO), onions can help treat atherosclerosis and improve appetite. Furthermore, studies have proven that people with allergic bronchitis, chronic asthma, coughs and the common cold can immensely benefit from consuming diets rich in onions.

Onions are rich in vitamins, minerals, sulfuric compounds, quercetin and dietary fibers, hence their medicinal properties. Moreover, they act as insect repellents and can be used to treat insect stings and bites. With all these benefits, you should plant onions at home in your garden, backyard or indoors.

A Guide on How to Plant Onions at Home

Onions’ hardiness, high yield, and easy storage make them a must-have in any avid Gardener’s list of crops to grow.  Be aware, however, that onions planted from seeds can take 5 months or more to reach maturity.  So, if you’re starting from seeds, sow seeds indoors 8 to 10 weeks before the last average frost date—this is usually in February or early March. 

If you’re starting with sets, plant them in late April or May. With Green Valley fabric grow bags, you can do this indoors and simply carry your grow bag outside once weather permits. With no transplants necessary, your seedlings are less likely to suffer from transplant shock.

Our pop-up plant cover will allow you to move seedlings outside in their grow bag weeks earlier if you need to free up space in your home.

Factors to Consider When Growing Onions at Home

Whether you want to plant onions indoors or outdoors, consider the following factors for a good start:

  1. Planting Zones

Onions can do well in zones 3 to 9. Find out if your zone is conducive for planting onions at home on the USDA Plant Hardiness Zone Map website.

  1. Type of Onion to Plant

There are various types of onions you might want to plant at home as follows:

  • Sweet Onions - Usually large, sweet onions are less opaque with a slightly lighter skin color.
  • Yellow Onions - Popular for their strong, sulfur-like scent, yellow onions are brown on the outside and ivory white on the inside (the flesh).
  • Shallots - These onions are small with purple flesh and brown skins on the outside.
  • White Onions - Unlike yellow onions, white onions are sweeter and milder with a white skin.
  • Green Onions - These are onions without bulbs.
  • Red Onions - These onions are deep magenta on the flesh and skin. Since they are sweet and mild, red onions are often eaten raw.
  • Leeks - Resembling overgrown scallions, leeks have long leaves and small bulbs. This type of onion is often used to prepare soups and sauces.

Whether you choose bulb or green onions, you can grow them in containers, pots or plastic water bottles. Your geographical location is a determinant factor when choosing the type of onion to grow.

  1. Onion Varieties

Choose between long-day (14-16 hours) and short-day (10-12 hours) onion varieties. You can also consider intermediate-day (12-14 hours) varieties. Whereas short-day varieties do well in the south, long-day varieties are best grown in the north.

  1. Growth Requirements
  • Temperatures - Onions require cool temperatures for early development and warmth or sunshine as they mature. 21 degrees F is the ideal temperature for growing onions, but anything below 18 degrees F can kill your plants.

Onion seeds emergence and germination occurs at a temperature range of 55 to 83 degrees F. Onion cycle in the tropical regions take 90 to 150 days after transplanting while in warm temperature regions, the cycle lasts 9 to 10 months.

Onion bulb development requires high temperatures and 12 to 15 hours of day. The right onion planting density and early leaf cover can promote big bulb sizes and high yields, respectively.

  • Light - Onions require sufficient light. If you're growing your onions indoors, place the garden near windows to ensure they get enough light. You can also use artificial lights to supplement natural light to ensure what your onion crops get is enough to support photosynthesis.

Consider grow lights, incandescent or fluorescent lights to ensure your onions get sufficient light during bulb development. However, make sure the specific onion variety only gets the right amount of light after which you can put off the lights. Onions also require dark hours to enable them complete their day-night growth cycle.

  • Plant Spacing & Depth - When growing onions, let the plant spacing be three inches. Plant each onion 6 to 10 inches deep to promote root and bulb development. However, you can grow smaller onion varieties or scallions with less spacing between plants.
  1. Selecting the Right Container

Choose a 6-10 inch deep container with width size of your choice based on the space available indoors. The right depth in your chosen container ensures your onion roots increase in size and quality. Bottle onion gardens are popular for their novelty and attractive looks.

  1. Soil Preparation & Water Management

Fertile, well-structured soil is the key to optimal onion growth and high yields. Prepare a seedbed with fine soil if you intend to grow your onions from seeds for optimal germination and plant development.

Onions generally have short, sparse roots with few hairs, hence the need for moisture and nutrients just 10 inches from the top soil. Onions require sufficient water to grow and produce high yields. During drought, although onions can survive, they undergo stress and are likely to split or develop many bulbs on just a single plant.

Onions require up to 3 inches of water on a weekly basis during early plant development. This is unlike the late development or maturity period when they have low water requirement to prevent skin cracking and speed up maturity.

Mulch your onions with straw or grow them with wheat or barley to minimize soil erosion, especially if grown on light soils. If you intend to grow onions in your backyard or garden, make sure it's free from stones and clods that can hamper the efficiency of herbicides, growth and mechanical harvesting.

The right soil pH for growing onions is 6 to 7. However, if your soil is organic, the pH can be as low as 4. Soil with a pH of 5.5 lacks molybdenum and magnesium whereas a pH above 6.5 lacks manganese, zinc and iron.

Avoid salty water and saline soils because onions are sensitive to salinity, leading to reduced yields. Fertilizers with chlorides are also not allowed because they reduce the growth of onions. Opt for sulfate and nitrate fertilizers to boost the growth of your onions.

Note that you can easily grow green onions in water indoors without using soil. You can grow them in a glass or bottle of water.

  1. Onion Starter PlantnSets or Seeds

Choose to grow your onions from sets or seeds. If you have sprouting onions in your kitchen, use them to start your indoor onion garden instead of throwing them away. Whichever you choose, allow your plants to grow for at least 4 to 6 weeks.

Planting Onion Sets

                                                     Planting Onion Sets

The sets need to sprout properly while the seeds require time to germinate. Although sets are easy to plant as they've been started, they might not give the best yield.

  Onion Seeds

                                                   Onion Seeds for Planting

On the other hand, onions grown from seeds flower in the second year as they're bi-annual plants, giving yield to large bulbs with longer storage life. Onion starter plants or sets are also prone to rotting, hence the need for you to plant your garden onions from seeds.

How to Plant & Care for Onions


                       A Video on Onion Seeds Sprouting, Ready for Transplanting

What you'll need... 

  1. Green Valley Grow Bag 
  2. Seeds or sets/Kitchen onion scraps
  3. Potting mix soil
  4. Seed Starter
  5. Trowel
  6. An extra source of light (optional)

Table 1: A Table Comparing What it Takes to Plant, Care for & Harvest Onions

Planting Care Harvest
  • Pour soil (and seed starter if necessary) into your grow bag; or, make sure your raised bed has about 10-12 inches of loose, loamy soil.
  • Plant seeds about ¼” away from each other, about ¼” deep in rows. Rows should be 4”-6” apart.  If you’re starting from sets, plant 3-4 small bulbs about 1” deep together—Brady Bunch style; groups should be 6” away from each other.
  • Keep soil moist. If the soil is dry when you’re planting, water immediately.
  • Place in direct sunlight or under plant lights.
  • Remember! Seeds can take up to two weeks to germinate as in the video above (do not despair!)
  • These little guys need water and warmth to germinate and grow!
  • Make sure they get lots of sun.
  • Add general nitrogen fertilizer every 2-3 weeks to promote bulb development.
  • Move seedlings outdoors once they have 3 leaves.
  • Use mulch to reduce watering levels as it retains moisture and suppresses weeds.
  • Onions mature when their tops begin to fall over or yellow.
  • Once most leaves have fallen over, bend the rest over manually, stop watering them and wait for 2-3 days.
  • Pull your onions out and let them sun dry for about a week.
  • Harvest and store somewhere dry with sufficient air flow.

    Onion Life Cycle

    Onion seeds are planted in the first year and they germinate in 7 or 14 days. The onion develops leaves as it continues to grow for photosynthesis. The onions use the energy produced during photosynthesis for bulb development in spring, fall and summer.

    If not harvested, onions can remain dormant underground in winter. During the second year, they flower. When temperatures warm up in spring, onions flower, get pollinated and develop seeds.

    Note that early onion dormancy due to sudden cooling in summer can cause your onion plants to flower despite being in their first year of growth.

    Onion Life-cycle

                                                                  The Life Cycle of an Onion

    Provide Protection for Your Onions

    Use hand weeding, herbicides and inter-row cultivation with other crops to help keep your onion garden weed free. Since onions generally take time to grow after transplanting, they cannot compete well with weeds for nutrients, water and other necessities for growth.

    Make sure your soil is sterilized and use nematode-free seeds and good plant rotational practices to keep nematodes and eelworms from your onion plants.

    Whereas the former restricts uptake of moisture and nutrients through roots and stems, the latter attacks stems, causing damages, plant distortion and death, including shoot twisting. Onion thrips, on the other hand, are common in regions with warmer climates.

    Thrips don't just damage onion leaves, but also cause stunted growth. Use insecticides to kill onion maggots or fly, including thrips. Control of fungicidal and bacterial diseases is also important to improve your crop yield.

    Fungicide sprays, deep cultivation, soil sterilization and wide rotations can control most disease problems. Leek rust, onion white rot and downy mildew are some common problems you can expect to face while planting onions at home.

    Onion Harvesting

    Onions are harvested in fall when the leaves yellow, dry and fall over. According various studies, you should harvest your onions when they still have between 30% to 40% foliage. This increases their storage life.

    Strike a balance between reducing the quality of your bulbs in storage and getting maximum yield to harvest your onions at the right time. Do not over dry the onions to prevent them from balding while in storage. Harvest in late summer.

    Loosen the soil and pull your onions from the container, pot or raised bed and dry them in the sun. Remove the roots once they're dry and ready for storage.

    Onion Storage

    After harvesting, onions can be cured outdoors. During the curing process, the onions should be covered in your garden or backyard, but must never be left out for too long. Controlled storage with the right atmospheric conditions can help preserve the quality of your onions.

    Low oxygen levels in storage minimizes sprouting while low CO2 levels prevents fungal sporulation. Keep humidity levels between 65% and 70% and temperatures at 34 degrees F to prevent fungi from spreading and minimize respiration, respectively.

    You can store your harvested onions for many months. Keep the in a cool, dry place with proper ventilation for up to one month. Neither store your onions under the sink or in a refrigerator as the high moisture level can make them soft and thus spoil them.

    Keep cut, but unused onions in an airtight container or plastic bag for refrigeration. Use them in two to three days. Inspect your onions regularly during storage for discoloration or slimy substances. Discard those that are either discolored or have become soft and slimy.

    Refrigerate spring onions for up to seven days. If you want your onions to stay fresh for up to a year, cover them in foil and refrigerate. Never store your onions near pears or apples for prolonged storage.

    How to Avoid Onion Bolting

    Onions germinate from a seed to a plant then a bulb during the first planting year. They grow again during the second year, producing flower spikes. Seeds are produced when the flowers are fertilized, completing the onion cycle. Heat treatment can help prevent onion bolting.


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