Don’t plant onions until the temperature stops dropping below 20 F (-6. 7 C). [1] X Research source You can find the last expected frost date for your area by checking weather stations, a farmer’s almanac, or a government meteorological website.

You can test the pH of the soil with a home soil test kit or with a pH meter. Use lime to increase the pH of your soil, and sulphur to lower it. [3] X Research source Amending the soil with compost will add nutrients and help the soil drain better. The ground must be loose to allow sulfur to drain through; otherwise, the onions won’t be as sweet.

When growing sweet onions, avoid sulfur-based fertilizers, because these will make the onions more pungent. [4] X Research source

Instead of growing the onions in rows, you can also plant them in raised beds that have been amended with compost and fertilizer. Planting sweet onions in rows or raised beds is important because it will help the water drain better, and this will produce sweeter onions. In a container, you have complete control over the soil medium, so it’s not necessary to create rows before planting.

An onion set is a small onion that was grown the previous year and dried.

When the onion bulbs start to grow, sweep the mulch away from the bulbs to keep the onions dry.

You’ll have to provide even more water if you didn’t add a top layer of mulch. [7] X Research source Water less if the leaves start to yellow prematurely, because this means they’re getting too much.

Side dress the onions again when the tops reach about 8 inches (20 cm). [8] X Research source Use a nitrogen-rich fertilizer like blood meal.

Depending on the variety, the onions might be ready anywhere from 90 to 110 days after planting. [10] X Research source

Make sure you harvest the onions by late summer, because the cooler temperatures of fall will cause them to spoil. [11] X Research source

During wet weather, cure the onions inside in a well-ventilated area. Curing is the process of allowing the skins to dry, and this will help make for longer storage. Because sweet onions don’t keep as long as pungent onions, you don’t have to cure them for as long.

Sweet onions don’t tend to last as long as regular onions, and you should use them within six weeks. To extend the shelf life of the onions up to 8 weeks, wrap them individually in paper towels and store them in the refrigerator. [13] X Research source