Growing onions 101

Bulbing onion flowering in late spring

Saturday, March 28, 2026

It is time to plant onion sets and onion transplants in the garden to get full size bulbs for harvesting this summer. 

You can order sets on-line, get them in big box stores, local nurseries, local farm supply stores and local hardware stores at this time of year.  Your local stores should have the type of onions that will bulb properly for your latitude.  Onions set bulbs based on the hours of daylight.

If ordering on-line, know what daylight zone you are in to get the ones that will develop into full bulbs for your zone.  They start forming bulbs when daylight hours hit a minimum. For long day onions, it is 14 hours. For intermediate, it is 12-13 hours. Short day onions are 9-10 hours.  You also need to get them planted this month to insure optimal size for harvesting.

 I would have thought that long day onions would be for the South, but this is wrong.  The North gets the really long summer days (think of Alaska in June with no darkness).  Long day onions should be planted in states north of the Oklahoma/Kansas border (approximately 36 degrees latitude).  Intermediate day onions are planted in the middle of the US and short day onions in the South (like Vidalias).

I live in Kentucky so right in the heart of intermediate day onions.  I can plant long day onions, but should have gotten them in the ground as soon as the soil could be worked last month so that get a good root system for making large bulbs when peak daylight occurs in late June.

This year, I bought sets from a big box store and started seeds of interesting intermediate types.  For sets, the bulbs need to be firm to still be viable.  I planted my sweet onion sets yesterday and will plant my seedlings in a couple of days.  I have the seedlings hardening off on the back patio to get used to the cooler temperatures and increasing time in unfiltered sunlight.

If ordering sets or plants on-line, they will send them to you when it is time to plant in your area.

Plant about 1" deep in soil rich with organic matter and well-drained, 6" apart for individual cloves or bulbs.  I already added the phosphorous and potassium my soil test said to add so I will put a handful of blood meal for nitrogen under each bulb at planting.  If you haven't done a soil test, you can add a balanced fertilizer in each hole as you plant.  In the spring, continue to side dress with nitrogen every 2-3 weeks when growing resumes.  If using blood meal, use 1 cup per 10 feet of planting.  Alliums prefer a soil pH of 6.5-7.

I plant potato onions, shallots and Egyptian walking onions in the fall to give them the winter to develop good root systems for harvesting this spring and summer.

For more on onions, see 

Onions-everything you need to know to grow 'em