How to Grow Yellow Onion Bulbs in a Pot

Drill six to eight ¼-inch diameter holes in the bottom of an 18-gallon plastic tub. The holes provide drainage for the soil.

Mix ½ cup of slow-release 14-14-14 fertilizer with 18 gallons of soilless potting medium. Add enough water to the medium to evenly moisten it and place it inside the tub.

Plant the yellow onion sets 1 inch deep in the tub, spacing them 4 inches apart in all directions. Alternatively, plant onion seedlings in the tub at the same depth they were growing at previously, spacing them 4 inches apart.

Set the tub in an area that receives full, all-day sunlight. Choose a location near a water source to simplify irrigation and maintenance.

Water the soil when the top 1 to 2 inches feels dry, usually once daily in warmer weather. The potting medium is moistened throughout once water begins to trickle from the bottom drainage holes.

Fertilize onions every two weeks with a soluble fertilizer, beginning six to eight weeks after planting. Use a 15-30-15 blend at half the label recommended rate.

Harvest the onions in late summer after the tops fall yellow and fall over naturally. Dry the onions in a shady location to dry for four to six hours.

Lay the onions on screens to finish drying for storage. Place the screens of yellow onions in a warm, well-ventilated area and dry for two to three weeks, or until the stem dries out completely and the skins feel papery.