Make your own Onion Powder & Garlic Powder #easyrecipes #homemade #onionpowder #garlicpowder #fyp Onion Powder & Garlic Powder Onions Garlic Slice onions and Garlic as thin as you can. Place the sliced onions and sliced garlic evenly on a dehydrator sheet or a baking sheet and dehydrate at 140° for 8-10 hours or untill fully dried. Once dry grind onions into a fine powder; do the same with the dried garlic. Store onion powder and garlic powder in airtight containers. Homemade onion powder lacks preservatives so it will usually last between 6 and 8 months and should be kept in the refrigerator to maintain flavor. Homemade Garlic Powder will usually last between 1-3 years if stored in an airtight jar and kept dry properly.