HOW TO GROW ONIONS FROM SEED: For best results, sow seeds indoors 8-10 weeks before last heavy frost. Grow on a sunny windowsill or under plant lights. When plants are almost the thickness of a pencil, plant out in the garden. Space seedlings 2-3" apart. OR sow directly in the garden in early spring as soon as the soil can be worked.Dig mature bulbs when most of the tops have fallen over. Cure in a warm, protected spot for 2-3 weeks. Trim tops 1 in. above bulbs. Store in airy, dry, cool, frost-free place.