Homestead Backyard

How to Grow Onions from Seed

How to Grow Onions from Seed

Most gardeners start to grow onions from sets. These small and immature onion bulbs are preferred by many as growing them is incredibly easy. However, if you want to expand your variety horizons, you will understand that onion sets offer limited choices and turning to seeds is the best thing you can do.

Growing onions from seeds allows you to pick from a wide variety and find those that suit your own needs like the desire for late season keepers or early season sweet onions. The colors range greatly from pure white to dashing purple and many yellow shades. Sizes and shapes vary a lot too. Here is a simple guide on how to grow onions from seeds and be a successful gardener.

  1. Start off with fresh onion seeds

It is possible to keep onion seeds for over two years provided they are stored in a cool and dry place and in a seed storage box that is well monitored. However,
it is advisable that you grow your onions from fresh first year seeds as they germinate best. The rate of germination falls considerably with the aging of the seeds. Planting fresh seeds assures you the highest germination.

How to Grow Onions from Seed

  1. Provide your seeds with bottom heat

We all know that heat is essential for germination to take place and providing some will boost the germination and yields of your onion seeds. By availing this heat, your onion seeds are going to germinate very quickly. For fast germination, provide your onion seeds with a temperature ranging between 20 and 25 oC and drop the temperatures lightly at night. It is also advisable that you enclose your newly onion seeded containers in plastic bags so as to maintain moisture and also provide bottom heat as well. By doing so, you will be thrilled to know that your onion seeds will start germination within the first week.

  1. Clip off the seed husks

Once the germination has occurred, you will realize that your indoor grown seedlings perform very poorly when it comes to getting pulled from the seed. In the long run, the small end will pull out of soil and the black remains weigh them down. You can do some rescue on your onions by simply snipping the loop by half and then pulling the small end out and then discarding it.

  1. Provide under lights

It is advisable you remember that when you are growing onions from seed, you will need to provide them with bright supplemental light. Using a 2 bulb fluorescent fixture will do amazingly well and you can keep the light on your onions for a period of twelve hours in a day and they will do amazingly well. Position the light within 2.5 cm or 1 inch of the onions. Make sure that you also trim your onions back everyday to about 7 cm tall and this will help ensure that they don’t fall over. Using scissors is advisable and will ensure that a clean cut is achieved.


  1. Know when to transplant your onions

When your onion seeds have grown, it is essential that you know the best time of transplanting them. Experts always advise that transplanting should be done upon the appearance of the third leaf. So once you confirm that your onion seedlings have three leaves, transplant them into containers gently which are about 10 cm deep.

You should know that your onion seedlings will grow more rapidly if you provide them with sufficient space for their vertical root to grow unlike those that are confined to the shallower quarters. Even though containers that are made from milk carton bottoms or the large paper cups might not be as pretty as such, they are nevertheless the best you can use for holding lots of your adolescent onion seedlings.

  1. Trimming of the leaves

The seedling leaves will also need to be trimmed off after sometime. Once you have transplanted your seedlings, the onions shed off the seedling leaves and you should snip and remove it as a way of ensuring that your containers stay tidy. It is important you know that your onion seedlings are going to respond well to transplanting when they make a strong upright growth. You should keep this trimmed back to at least 12 cm high.


  1. Providing light is essential

For your onions to continue growing healthily and quickly, it is essential that you provide them with maximum light. Sunny days provide the best light to your onions and it is essential that you move your adolescent onions outdoors anytime there is warm sun. You will however need to shield them off from the wind and use plastic covered tunnels or a cold frame and they will truly love it.

  1. Protect from chilling

After sometime, you will need to be providing your onion seedlings with sunlight on 24/7 basis. At night, the temperatures should be over 8 degrees Celsius. Avoid exposing your onion seedlings to temperatures below 10 degrees Celsius as this can lead to the bolting of the onions instead of producing big bulbs.

  1. Use fertilizer/ rich compost

The roots of onion seedlings are mainly concentrated just blow their bulbs and this is something that you will need to keep in mind when you are preparing your planting bed. Here, it is a good idea that you make some deep planting trenches which you should line with composted organic fertilizer and rich compost. This technique is known as banding fertilizer and aims at placing the nutrients where the onions can utilize them in the best way possible.



Keep in mind that onion seedlings are heavy feeders and besides the initial feeding that you provide at planting time, using fertilizer and side manure dressing is something that you should consider doing. Onions also need to be provided with adequate potassium otherwise their necks are going to thicken and their bulbs won’t be storing well. Ease up fertilizer and water to encourage dormancy as the onions continue maturing.


Pelleted Seeds Onion Bridger D2545PA (Yellow) 100 Seeds by David’s Garden Seeds

Botanical Interest – Onion Bunching Italian Red Heirloom Seeds 1 Gram

Organic Heirloom Seeds Non-gmo Non-hybrid


Scroll to Top