Ask Burton: This week, a question about one of our favorite vegetable garden crops. Q: I plant onions every year and I just can’t get them to grow as large as I want. How can I do better?

A: There are several things which can help. We’re going to go over how to do this in your existing vegetable garden.

Prepare the planting area where you intend to plant onions by breaking the soil to a 6-8″ depth. Add some compost to the soil if the soil is getting hardened up, and spread ferti-lome Gardener’s Special fertilizer (11-15-11) over the area at the rate of 1 level cup of dry fertilizer for every 5′ by 5′ area. Turn the fertilizer into the top 3-4″ of soil.

Plant onions early – which, at this point, means RIGHT NOW. They need some time to get a good sized onion worth eating when they finish up in May. Plant onion slips about 3/4″ deep, but no deeper than 1″. Onions planted too deeply won’t grow correctly.
Keep the onion bed adequately watered, and as soon as your onion sets have started to root in and send up a few more leaves each, top dress the bed with 21-0-0 (ammonium sulfate), using 2/3 of a cup of the material over that same 5′ by 5′ area. Water vigorously after applying this fertilizer. If you prefer a sweeter onion, use calcium nitrate (15.5-0-0) instead – the sulfur content of the ammonium sulfate can make onions taste sharper, having a stronger “bite”.

When the necks of the onions begin to get weak, and the greenery begins to flop over, you’re coming up to harvest time. Pull your onions, and leave them outside to dry for a few days. (I use the bench you see in the photo there to dry mine.) This drying time is important to cure the onion, preventing mold from attacking your stored onions. If any of your onions flowered, try to use those first, as the blooming stem won’t let the onion store as well.

View our Vegetable Planting Guide here

View our Successful Onion Guide here

Burton specializes in diagnosing and solving plant problems. If you have a question for Burton, please email him at and include photos showing the problem.