Hardening off prepares seedlings that are started indoors to handle the temperature fluctuations, breezes and elements of the outdoor garden. In general seedlings are brought outdoors and placed in a protected area, such as on a porch, for a couple hours each day and brought indoors at night. This continues for one to two weeks with the time outdoors slowly increasing until it is time to put the plants in the ground. If this isn't possible, it is possible to harden off the seedlings directly in the garden bed using frost blankets, also known as floating row covers.
Begin hardening off one week before you normally would plant the seedling into the ground. For most plants, wait until daytime temperatures have warmed and night time frost is unlikely.
Set the plants outside in a protected area for two hours on the first and second day of the hardening off process. Bring them indoors before night fall.
Set the seedling pots in the garden where they will be later planted. Set the pots close together in rows no more than 2 inches apart.
Leave the plants uncovered for four hours on the third and fourth day. Place the frost blanket over the plants after the heat of the day has passed, making sure it doesn't actually set on the seedlings. Use stakes or the included hoops if available to keep the blanket off the plants.
Leave the ends of the blanket unsecured if temperatures are above freezing at night. Otherwise, weigh down the ends of the blanket with soil or rocks so it is completely sealed to keep the frost out.
Leave the plants uncovered for an hour longer each day but continue covering at night. Follow this process for at least one week and preferably two before stopping use of the cover.
Water the plants as needed while hardening off. Water thoroughly until water runs from the drainage holes of each plant the day before transplanting to the garden soil to avoid shock.