If you enjoy adding fresh onions to your salads but don't have adequate space for a garden, consider growing your onions in pots. Onion sets planted in containers are easy to grow and more reliable than onion seeds. Your container-grown onions will look and taste just as good as those grown in the ground.
Choose lightweight plastic pots for your onions, which will make moving the pots around a lot easier. Wide-mouthed pots that measure at least 20 to 25 cm deep should suffice for smaller onions.
Fill the pots with organic potting soil. Organic potting soil is airier than traditional soils and also contain more nutrients. Plant the sets in the pots with the leaves above the soil line. Onion sets require planting 10 cm apart from one another with an additional 7 cm of open soil, so plant accordingly. For instance, if your pot is 38 cm wide, you will have enough room for two onion sets.
Place the onion pots in an area that will receive at least six to seven hours of bright sunlight per day. If you choose to keep your pots on your deck or patio, keep in mind that the onions will not tolerate temperatures below 13C. When the temperatures drop the onions must move indoors.
Water the potted onions every two to three days, providing up to 5 to 8 cm of water per week. Sun exposure will dictate how often your potted onions will require watering. Onions grown in sunnier locations will require more water than those exposed to less sun.
Feed the potted onions a diet of slow-release fertiliser per label instructions. You can also add mature compost every two weeks to the containers, instead of fertiliser, if you prefer. Harvest the onions when their tops begin to bend and turn yellow.
If you need to bring the onions indoors, place the pots in a window that receives plenty of bright sunlight during the day. If you do not have such a window available, set the pots under grow lights.
Do not overwater your onions. Allow the top layer of soil to dry out between watering.