Onion Growing Tips


Onions are so much fun to grow because they require relatively little attention and have a wide range of uses in the kitchen.  By keeping a few things in mind, you will be able to have a heavy harvest of onions in the fall (or throughout the season if you choose to pull them when they are immature).


1. Choose the right kind of onion for your growing area.  When looking for onions, you may see terms like ‘short day,’ ‘long day’, or ‘intermediate day’ on the product tag.  For all of Montana, long day onions are the best option.  The term long day refers to the amount of sunlight needed to trigger bulb formation.  Northern states receive more light hours in the summer than southern states.  Long day varieties that Green Thumbs supplies as transplants in the spring are Walla Walla, Candy and Red (with more options to be added as spring nears).

2. When preparing your garden bed, be sure to remove any weeds as onions are not very good competitors.  Tilling the top 6-8 inches of soil may be necessary to break up any soil that is compacted (and remove some weeds).  Onions, like all plants, will need fertilizers.  If possible, test your soil to see exactly what nutrients need to be added back to the soil.  If you cannot test your soil this season, consider adding a fertilizer that has a NPK level with moderate nitrogen and higher phosphorus levels and with higher sulfur content as onions are sulfur loving.  Down to Earth’s All-Purpose Mix and Garden Gypsum should provide adequate plant nutrition in most cases.

3. Plant your onions in a space that receives full sun.  Place the immature onion plants roughly 1 inch deep and 3-4 inches apart and in rows that are at least 6 inches apart. Do not plant the onions too deep as that will not allow for bulb formation.  If possible, run a drip irrigation line between each row to maximize consistency in watering.

4. Trim the leafy tops off of your onions.  Removing a portion of the green, above ground part of the onion leaves helps the plant to put more energy into the formation of bulbs.  After you cut the top 3-4 inches of green tops, you can use them like chives! They are delicious in an omelet or as a garnish for mashed potatoes!  Note: Do not remove the whole onion top. Make sure there are always at least 4-5 inches of green leafy top left from chopping.

5. Consider starting seeds indoors in February or transplants in the spring.  Avoid sets if your goal is to grow large storage type onions.  While sets can be a good option if you are looking to grow smaller onions or green onions, they tend to bolt more quickly and easily than onions started from seed or from transplants and therefore do not become as large.


Stay tuned for an onion harvesting and curing guide later this summer!

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