Radio Tips
August 4, 2023

Onions & Onion Sets

Onions are a gardening option that is easy to grow and that stores well. If you’ve got a garden this season, you should consider adding onions to it.

There are THREE common types of onions: Long Day, Intermediate Day and Short Day. This refers to the amount of light each onion variety requires daily to grow well.

So check the label on the bag of seeds you buy and make sure that they are ideal for your zone. Herein the PNW, we want to get Long Day Onions.

Traditional Onion Set are 1”bulbs with a root side and stock side. These onions are about 1 year old and are ready to plant the day you bring them home. They need no extra care or prep before planting. Just make sure to plant each bulb with the “root side” down, and the “stock” side just barely sticking up out of the soil.

A “Transplant” onion set is grown from a seed and planted in the same season. Commonly started in a seed starting tray like the one seen above.

Whether you use a peat disk or you choose to mix your own potting soil and vermiculite, the process is the same. “Over seed” each space. This would be 5 to 6 individual seeds per space or peat disk. Water thoroughly and place the covered seed tray in front of a window that gets plenty of sunshine. It’s highly recommended to use a miniature greenhouse.This will allow you to control the humidity and temperature for your onions. For maximizing your seed growth, both our stores also carry heat mats and LED Grow lights. Once your seeds have sprouted and are between 4” and 6” in height you’ll be ready for the next step.

At this stage of their life,some of the seeds will be smaller and possibly have poor rooting.This is why we chose to “Over seed”. Now we can thin each cell down to the two strongest onion blades in each cell. After a little more time, in the greenhouse the root systems will be able to fill out the starting tray cell. Now that your root systems are strong,they will have a much greater chance of survival in your garden.

Now it’s time to gently separate each of the onions taking care not to damage the root systems on any of the individual plants. Consider hardening your onions plants for a week by exposing them to the outside temperatures and elements.

Now it’s time to plant your onion starts or sets. Spacing them about 4” apart is ideal for maximum bulb growth.

Onions like plenty of water and plenty of fertilizer. Starting with a 20-20-20 for high phosphorus & potassium while they’re young. This will really help great root development. Then later in the season switch to something with ahigher nitrogen content like a 15-0-2 which will feed them nicely.

Fun Fact

Each leaf on the stock represents a layer on that onion. The more leaves, the larger the onion!


Harvesting your onions at the right time will allow you to have the longest storage life for your onions. Onions are ready to harvest when the stalks start falling over. When 50% of your onion stalks have fallen over, they are telling you that they have stopped growing and are ready for harvest. Once this occurs, you’ll want to be sure to harvest them quickly, especially if there is rain/moisture coming. Leaving bulbs in the ground that have completed their growing cycle, (especially in wet conditions) will allow for a greater chance of rot, mold or mildew issues.

If you see your onions starting to “bolt” or grow a blossom that will eventually turn to seeds, all of the energy will be redirected to the blossom. It’s the way it ensures it reproduces. This means that the energy you want directed to the bulb is being diverted and the bulb has stopped maturing. The bulb can even “split” at this point, and then it is no longer ideal for eating, curing or canning. So cut off the bolted stalks, and harvest those onions.

Curing your onions for long term storage

Sweet onions have a shorter shelf life vs. other varieties, even after they have been “cured”.

You’ll want to pick a spot that is not in direct sunlight, as direct sunlight can actually “sunburn” your onions (this goes for Garlic as well). You’ll want to find a warm area that has really good circulation and airflow. A great option for curing is to hang up a hanging wire panel.

Above you’ll see a wire fence panel being used to hand the onions. If the stocks are still fairly straight, you can hand them “upside down” with the stalk pointing downward. This is commonly thought to help pull moisture away from the bulb faster. To hang the onions, simply draw the onion stalk through the opening of the fence panel and bring them back through the opening directly underneath. This will help keep even the heaviest onion bulbs from slipping and falling off. If the shape is not correct or you are worried about wind just tie the onion on with string.

Another idea would be to use a window screen which allows great ventilation as well.

Here you’ll see that a window screen was set up on saw horses, to act as a table. You can use any wire shelf, or sturdy fencing material that will also allow for the same great airflow and circulation. Make sure to leave enough space between each bulb so they are not touching and get full airflow. If one onion shows signs of decay, mold, mildew etc. it will quickly spread from onion to onion when they are touching. If the bulbs are spaced apart from each other you can usually remove the individual “trouble” onion before it impacts the rest of your harvest.

Curing time depends on your weather and humidity levels. The more humidity and/or rainstorms in your area, the longer the curing time will be. The rule of thumb is 14 days, but this could take up to 21 days if heavy moisture is present. You’ll want to make sure that they have fully dried before bringing them inside for long term storage. When the stalks are completely dry, and the exterior skin is completely dry (and any residual dirt is more like dust that can be blown away) your onions are ready to bring inside for storage.

Come into either of our Monroe or Snohomish locations to get your onions, seed starting kits, or fence panels. Our staff is here to help you get set up for a great year!

We’ll see you at the Coop!

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