How to Grow Onion Plants

Onion plants are a popular garden vegetable that can be grown in both the spring and fall. Onions are known for their strong flavor and long storage life, making them a great choice for any vegetable gardener. Proper preparation, planting, and care are essential to get the most out of your onion plants. 

When planting onions, bury the bulbs at least two inches deep and space them four to six inches apart. Planting in rows is recommended, and be sure to leave enough space between the rows to allow for weeding and harvesting. 

To keep your onion plants at their best, regular watering is essential. During dry periods, water deeply to ensure that the soil remains moist but not soggy. Onion plants are also heavy feeders, so be sure to give them a balanced fertilizer about every four weeks. 

Growing your own onion (Allium cepa) plants can be a rewarding experience, providing you with fresh onions for many months throughout the year. 

Let’s look at the steps needed to cultivate healthy onion plants that produce delicious, flavorful onions.

Onion Plant growing in a garden.

Choosing Your Onion Variety

Choosing the right onion variety is key to a successful harvest. Depending on your region, you may want to consider short-day onions, which form bulbs when days are 10 to 12 hours in length, or long-day onions, which require 14 to 16 hours of daylight. Green onions and scallions have a milder flavor, but they must be harvested before they are fully mature.

Select varieties that give you as much time as possible to grow large leaves before bulbing to ensure you get the best results. The variety must also suit your soil and climate conditions. Planting onion sets or seeds is the best way to ensure success, and spacing should be 4 to 6 inches apart, depending on the size of the variety.

Preparing Soil and Site Selection

Once you have selected the variety of onions you would like to grow, it is time to prepare the soil and select a suitable site. Onions grow best in full sun with rich, well-drained soil and plenty of organic matter.

To prepare the soil, turn under animal manure or compost to help give your onions the best start. When it comes to spacing your onion plants, they should be placed approximately 4 inches apart. Onions also need firm and finely textured soil in the seed bed for good germination and stand establishment.

As the onion begins to bulb, be sure that the soil around it is loose so that it is free to expand. Finally, onion plants will benefit from a light application of fertilizer and mulch to ensure their success.

Planting Onion Sets or Seeds

Once you have chosen the onion variety, prepared the soil, and selected the site for planting, it’s time to plant your onion sets. Onion sets are immature bulbs that have been grown from seed in mid-summer of the previous year. The partially grown bulbs are pulled from the soil and dried for storage before being planted.

Plant onion sets 4 to 5 inches apart in rows 12-18 inches apart and no more than one inch below the soil. Planting sets will be easier than planting seeds as you don’t need to soak them prior to planting. Dig holes 1 inch deep and place the soaked bulbs in with the roots down. Cover them with the newly amended soil and water generously after planting.

If you are growing bulb onions, make sure to thin them out once they reach a height of 4-6 inches tall, leaving only 4-6 inches between plants. If you are growing green onions, make sure to keep them spaced 1 to 1½ inches deep and 2 to 3 inches apart. After planting, mulch around your plants and keep them well watered for optimal growth. With proper care and attention, your onions will be ready for harvesting in no time!

Watering Onions After Planting

After planting, it is important to keep onion plants well-watered. When planting onion sets or bulbs, be sure to till the garden bed with at least 2 inches of compost or planting mix. Generally, if light mulch is used, onion plants do not need consistent watering. Onions need about 1 inch of water per week, so if the weather is dry, you’ll need to water.

Onion seedlings should stay consistently moist until the plants take hold. Most onions require about 30 inches of water per season to grow a good crop with drip irrigation. The key is to provide about 0.3 – 0.4 inches of water per square foot per week, so use the “knuckle rule” to tell when it’s time to water. Keep watering even when they are bulbing.

Onion Plant growing in a fertile soil

Thinning and Spacing Onion Plants

This is essential to ensure good bulb size and a successful harvest. When planting from sets or seeds, it’s important to be selective and space the plants at least 6 inches apart in rows 4-6 inches apart.

If planting from seeds, sow them 1/2 inch deep and thin to 5cm (2in) apart when seedlings have grown taller. When transplanting seedlings, place them 1/2 inch deep and 4-6 inches apart, depending on the size of the mature bulb.

Uniform seed placement and in-row plant spacing are key to achieving good bulb size. Once thinned, extra plants can be used as green onions. Mulching can also help keep weeds down and help retain moisture in the soil. With proper thinning and spacing techniques, you can ensure a successful onion harvest.

Fertilizing Onions

Fertilizing your onions is an important step in growing a healthy crop. After preparing the soil and planting your onion sets or seeds, it is important to fertilize with a nitrogen-based fertilizer like ammonium sulfate or ammonium nitrate at the rate of one cup per twenty feet of row.

Work a handful of rock phosphate or bone meal into the soil before planting to provide phosphorous, which helps promote root growth and bulb formation. Additionally, apply a balanced fertilizer such as 10-20-10 just prior to planting.

Every few weeks after planting, fertilize with nitrogen to get big bulbs, but cease fertilizing when the onions push the soil away, and the bulbing process has begun. Finally, mulch your onions to help retain moisture and keep weeds away. With these steps in place, you will have a bountiful harvest!

Mulching Onions

Mulching onions is an effective way to maintain soil moisture and suppress weeds. After planting onion sets or seeds, spread a layer of mulch over the soil. Organic mulches, such as straw, shredded leaves, hay, or grass clippings, are best. Mulch should be applied in a thick layer at least 2 inches deep around each onion plant.

This will help keep the soil evenly moist during the onion growing season and reduce the need for frequent watering. Keeping the area around onions free of weeds can also help prevent disease and pests.

Harvesting Onions

Harvesting onions is a rewarding part of the process and can be done in a variety of ways. Depending on the type of onion you are growing, you can harvest onions for flavoring throughout the season by snipping the ends of leaves or harvest green onions when bulbs are no larger than the diameter of the leaves.

Bulb onion harvest time can begin when onion tops naturally fall over and brown, which is usually 100 to 120 days after planting. For the best quality, ensure your onions are harvested at the right stage and use the correct spacing when planting them.

In addition to correct spacing and site selection, proper soil preparation is key to successful onion growth. Composting your planting area helps provide the necessary nutrients for optimum growth and flavor.

By following these steps, you will be well on your way to growing delicious onions that you can harvest and enjoy all season long!

Storing Onions

Storing onions is important in ensuring that your onion crop lasts throughout the winter. Properly cured and stored onions will keep for several months if done correctly. After harvesting, cut off the roots and remove any loose skin from the bulbs. If you plan to store your onions as strings, cut the stems to within two inches of the bulb.

Place the bulbs in a mesh-type bag or spread them out so air can circulate. You can also use a cool, dark place such as a basement or garage for storage. Make sure to check your onions periodically for any signs of rot and discard any that are not suitable for eating.

With proper care and storage, your onions will last through the winter months and provide you with a satisfying harvest all year long.

Troubleshooting Common Onion Problems

Once your onion plants are established, it’s important to monitor them for any problems that may arise. Common onion problems include stunted growth, discolored leaves, wilting or droopy plants, and malformed onions. Planting the wrong onion varieties, incorrect planting times, or temperatures that are too warm can all lead to issues with your onion crop.

Root-knot nematode is a pest that can drastically reduce yield, and fungal and bacterial diseases such as soft rot, blight, and downy mildew can also be problematic.

To prevent these issues from occurring in the first place, it’s important to choose the right variety for your climate, plant at the right time of year, ensure proper soil preparation and site selection, water correctly after planting, thin and space plants correctly and fertilize when necessary. Mulching your onions can also help to keep them healthy.

If you do encounter any of these problems with your onions, it’s important to take immediate action to prevent the problem from spreading.

Can I grow onions from an onion?

You can grow onions from an onion! Start by cutting off a piece of the onion, leaving at least an inch of stalk and root attached. Place the cut onion in a sunny spot in your garden, ensuring that it has adequate drainage. Make sure to keep the soil around the onion well-watered – you’ll know it’s time to water when the soil feels dry to the touch. In 8-10 weeks, you should be able to harvest your onions!

How do you grow an onion step by step?

Here’s a step-by-step guide to growing onions:

  1. Choose the right onion variety for your climate and growing conditions.
  2. Prepare the soil by digging in some organic matter, ensuring it is well-drained and clear of weeds.
  3. Plant the onion sets or seeds at the right time of year, depending on your climate and the onion variety used.
  4. Ensure the plots have enough space between each set or seedling to allow it to grow properly – around 4 inches (10 cm).
  5. Water regularly during dry spells, but don’t over-water, as this will encourage disease and root rot.
  6. Mulch with leaves or straw to keep moisture levels consistent and deter weeds from sprouting up near your young plants.
  7. Feed with a high nitrogen fertilizer once every two weeks for bigger onions – this can be done either in liquid form or in pellets sprinkled around plant bases
  8. Once onion bulbs are ready, harvest them before they start flowering (called bolting) when they reach approximately 2 inches (5 cm) in diameter, depending on the variety grown
  9. Store onions in a cool dark place after harvesting until ready to use!

How long does it take to grow an onion?

Generally, onions take two to four months to mature fully. Depending on your climate conditions, onions are grown from seed usually take the longest, up to 140 days or more. Onion sets require about half that time, usually 70 – 90 days for full maturity. 

If you’re growing onions from transplants, plan for 60 – 80 days before harvest time arrives. For those looking for quick crops, scallions will be ready in as little as 30 days after planting if provided with adequate sunlight and water.

To ensure quality onions, use a variety of methods, such as crop rotation and soil testing to help prevent diseases and pests. Additionally, be sure to water your onion patch regularly and keep weeds at bay to ensure your onions receive all the nutrients they need for optimal growth.

How can I grow onions at home?

Growing onions at home is a fun, rewarding experience that can provide you with a fresh supply of the popular vegetable. Onions are incredibly easy to grow from seed or sets and will provide days of entertainment as you watch them progress through the growth stages. 

When planting onions, selecting a location in your garden that receives full sun and has soil with good drainage is best. If your soil is very heavy, consider amending it with organic matter to improve drainage and aeration. Planting in raised beds can also help ensure proper drainage and allow for more efficient watering.

Before planting, mix some compost into the soil to help give the young onion plants plenty of nutrients. When planting onions from seed, sow directly into prepared beds in spring. If using sets, these can be planted any time between February and early April. 

Plant seeds or sets about an inch deep in rows that are spaced 12 inches apart, covering them lightly with soil afterward. As they get bigger, thin young plants until they are spaced four inches apart. 

Water the soil well to ensure that the plants get off to a good start, and water regularly during dry spells. Onions are shallow-rooted, so avoid hoeing near them as you could easily damage their roots. Thin out any overcrowded seedlings to leave 4-5 inches between each plant.

Ensure weeds don’t compete for moisture and nutrients by regularly removing them from around your growing onions as required.  Mulch can also help to reduce the growth of weeds and conserve moisture. 

Fertilize your onion plants as needed based on a soil test or by using a balanced fertilizer such as 10-10-10 at the rate of one pound per 100 square feet. Apply nitrogen in small amounts throughout the growing season, starting when the onions are two inches tall.

Insects and diseases can be controlled with insecticides and fungicides as needed. These should be applied according to the directions on the label for the best results.

To aid pollination, gently shake the tops of onion plants every few days; this will also help deter pests such as aphids from taking hold. 

Harvesting begins when green foliage starts to yellow and fall over; when this happens, stop watering the onion bed for a few weeks so that their necks dry up and allow easy lifting from the ground without damage.

Use a fork to carefully lift out each plant before storing it somewhere cool and airy such as an unheated garage or shed for later use. Finally, enjoy your home-grown bounty!

Recent Posts