Onions need rich, loose soil to do well. Keep weeded and fed well as they have a shallow root system and don't like competition. Onions grown from seed or plants will usually yield higher-quality with fewer disease problems than if they are grown from sets. Plant seed about 1/4-1/2 inch deep in rows 18 inches apart. Thin to 4-6 inches apart. Plant times vary widely based on your location and onion type, generally early spring or indoors for long-day/northern varieties, fall for short-day/southern types. Soil should be at least 70F. Check with your local agriculture department for instructions specific to your area.