When growing spring onions, they can just as easily be planted indoor gardening in a pot as outdoors in a patch. The best time to plant them is the end of spring in May-June in northern hemisphere and November-December in southern hemisphere. Obviously it depends on your climate and situation; so many gardeners can plant earlier than this. There are also some varieties that can be grown in winter in milder climates or in pots indoors or in a greenhouse over winter.