image by sanja gjenero/sxc.hu
Indoor gardening is a viable alternative if you have no way to create a garden bed. Place containers on balconies or patios, or use them for an indoor garden if that's not an option. Growing onions successfully indoors is not much different than growing them outdoors. Giving them enough light is the primary concern for indoor gardeners but there are simple solutions to that issue. Experiment with different onion varieties to find the one that works best for you. March and early April are the best times to start your onion garden.
Use a large container that is at least 3 feet wide and 10 inches deep---such as a plastic storage tub. If using tubs, drill or poke holes in the bottom for drainage and use the lid for the storage tub as a drip tray to catch water run-off.
Fill the container with rich potting compost. Compost designed for vegetable gardening works well.
Work a general purpose fertilizer into the compost as you fill the container. Firm the soil with your hands but avoid compacting it too much or it won't absorb water properly.
Plant onion sets---these look like small onions---4 inches deep. Plant so the end with the dried stem is facing up. Space the sets at least 3 inches apart.
Water newly planted onions thoroughly. Keep soil moist but not soaking wet and avoid letting the top layer of soil dry.
Place containers where they have access to 6 to 7 hours of full sun. Use grow lights above the onion container if necessary to give them ample access to light.
Harvest onions late summer 2 weeks after the leaves have yellowed and fallen over. Avoid watering for 24 hours before harvest. Lift them carefully from the soil and lay on newspaper in a cool, dry place to for 2 weeks before storing.