How to Grow Onions

How to Grow Onions

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How to Grow Onions

Written by Gabrielle Smith

The common onion, also known as the Allium cepa, is a food staple that is beloved by chefs and novice cooks alike!

Easy to grow, tolerant to the cold, and requiring only full sun and well-draining soil, the onion is the perfect plant when starting a home garden.

Its resilient properties will have your garden filled with fresh onion in no time! Below is a detailed guide for the novice gardener on how to grow onion in your garden.

Botanical Name:Allium cepa 
Common Name(s):Onion, Yellow Onion 
Plant TypeBiennial herb
Place of Origin:Central Asia
Sun Exposure: Direct, full sun 
Watering Schedule:Every 7-10 days 
Seasonality: Summer through autumn
Bloom Time: Summer 
Toxicity:Unsafe for cats and dogs 


The common onion that we use today originates from Central Asia but has been cultivated under various different forms around the world. - It is believed that onions have been a staple of the human diet for almost 5,000 years!

In ancient Egypt, the onion was a symbol of worship. The circle within a circle layers of the onion were thought to represent eternal life with many onions found buried with mummies.

In modern times, the onions are typically used for cooking purposes but can also be found in cleaning products, deodorizers, and mosquito repellent. 


Find a place in your garden where your plant will get full sun for at least 6 or more hours. Once you have a sunny location, ensure your soil is minimum 40 degrees Fahrenheit to encourage growth and ensure frost levels aren’t too high to prevent growth.


In order to keep your onion seeds healthy and growing strong, ensure your plant’s soil is kept consistently moist. Water once a week when the first 2-3 inches of top soil have dried. 

Once your onion seeds begin to form a bulb, it is important to continue regularly watering your plant to ensure the soil does not become too solid and allows the bulb to grow and expand.


In order to grow and begin the germination process, onions need to be kept in higher temperatures. They prefer a range of 60-85 degrees Fahrenheit. 

As far as humidity goes, onions prefer an average level of humidity between 30-50%. 

Rule of (Green) Thumb: Cooler temperatures will delay germination and growth. 


Once you have the perfect spot for your little onion seedlings, you have to ensure that the soil is just right!

The perfect soil for your onion seeds is loamy soil. Loamy soil is well-draining and fertile soil; it is equal parts sand/silt/clay. - This soil type tends to be acidic but is high in nutrients and retains moisture very well.

Rule of (Green) Thumb: Soil with a pH level between 6 and 7 is perfect for this plant.


Once you have a sunny spot and have prepared your garden with loamy soil, it is time to sow your onion seeds!

Your seeds should be placed about an inch into the soil and about 3 to 4 inches apart. For each row of seeds, make sure there is about a foot to a foot and a half apart.

Onion seeds only last for one year so it is important to keep replanting the seeds annually to ensure your herb is ready for the next growing season. 

Rule of (Green) Thumb: You can begin sowing your onion seeds in your indoor garden at about Mid-February, early March. This will give your onion seeds time to develop inside and be ready to be transplanted into your spring garden by late April, early May once the soil can be worked. 


Once your onion seeds are sowed, the germination process begins. In colder weather, expect your seeds to take about 2 weeks to begin germinating. In warmer weather, the germination process will take 7 to 10 days.

Rule of (Green) Thumb: Germination is the beginning of the growth process of a seed into a sprout. 


With shallow root systems and the need for high levels of nutrients, onion seedlings require regular fertilizer application.

Three weeks after you plant your seeds, begin your first application. Once you have started fertilizing your plant, apply additional fertilizer every 2 to 3 weeks until the stem of the onion begins to soften (about 4 weeks prior to harvest).

High Nitrogen Fertilizer: 
Onions have moderate nitrogen needs but still require a nitrogen fertilizer to grow! - Nitrogen in fertilizer is used specifically for vegetative growth.

In a typical fertilizer there are equal parts nitrogen, phosphate, and potassium. In order for your onion plant to receive maximum benefits, you can use various different fertilizers to support your plant’s nitrogen needs. These include:
01. Blood meal
02. Cottonseed meal
03. Commercial 10-10-10 fertilizer.

High Phosphate and Potassium Fertilizer:
More important than a high nitrogen fertilizer, it is essential that your onion seeds are receiving large amounts of phosphate and potassium.

In order to ensure your plant is receiving adequate amounts of phosphate and potassium you can use the below fertilizer options: 
01. Blood Meal
02. Commercial 10-10-10 fertilizer
03. Ash wood: Leftover ash from your fireplace or campfire is high in vitamins such as potassium and phosphate. Ash wood can be used as an organic alternative to non-organic fertilizers such as the commercially made 10-10-10.


When harvesting onions, it is recommended to use onion seeds over onion sets.

Onion sets are miniature onions, typically 1 inch in diameter. Onion sets were onions that were grown in the previous season and were prevented from growing to full size.

Although planting these bulbs allows easier harvesting, they are typically a lot more expensive and have less variety then their seed counterparts. 

Onion seeds have a low cost and ability to grow various unique varieties. - Although a little trickier to harvest than their onion set cousins, the only major difference is starting the harvesting process within your indoor garden and transplanting your seeds outdoors after 10 to 14 weeks.


Arugula, like any other plant is susceptible to pests and diseases. Here are few to look out for: 

01. Thrips: These are tiny insects that may or may not have wings. They are typically brown or black in color, and damage your plant by sucking the nutrients from its leaves. If your plant has a thrips infestation you may notice stunted growth and black spots on its leaves. You can treat with an insecticide. 

02. Damping Off - Damping-off is a plant disease caused by several pathogens such as fungi and similar organisms. It will damage, and potentially kill your plant. This disease generally affects plants in the seedling stage when it is kept in a damp and cold environment without proper drainage.

Rule of (Green) Thumb: The best way to prevent future pests in your garden, is by rotating your crops. - Plant your seeds in a different location each season.


Though onions are a tasty ingredient for humans, they can be toxic to cats and dogs. Keep this veggie away from your furry friends, as ingestion may lead to vomiting, panting, or an increase in heartrate.  

Download the Flora App for more tips and tricks on how to take care of your onions!