Plants are like babies. When we start them indoors, we keep them sheltered and give them everything they need for success-consistent temperature, plenty of light, and the perfect amount of water. But eventually, they have to go out into the big outside world, and that's why you need to "harden off" your seedlings. Hardening off is the process of getting indoor-started seedlings accustomed to the outdoor environment by gradually exposing them to daily shifts in temperature, light, and water. As you prepare your onion, pepper, and tomato plants (or any others) for transplant, read your seed packet to know when to transplant outdoors as not at all crops tolerate frost. Below are some general guidelines to help your seedlings get all "grown up."
1. Begin hardening off 7 to 10 days before transplanting outdoors.
2. Start by placing your plants outside in a shady area protected from wind for 1-2 hours a day for the first 2 to 3 days. Bring them back inside at night.
3. For sun-loving plants, begin putting seedlings in progressively more sun for 2 to 3 days, being careful at first to avoid the harsh mid-day full sun exposure. If the plants you are hardening off are shade or part-shade plants, leave them in the shade or dappled sunlight. Do not put seedlings directly in wind, as they may dry out quickly or snap.
4. After 7 days, your sun-loving plants should be ready for full sun and staying outside at night if nighttime temperatures are above 45°F. When caring for cool season crops in small containers, err on the side of caution and bring them back inside when it is below 45°F. Cool season crops like broccoli, lettuce, greens, and cabbage can handle colder temperatures when planted in the ground.
5. After 7 to 14 days your plants are ready for transplanting. To reduce the stress of transplanting, transplant in the evening, or on a cool, cloudy day. Water plants immediately after transplanting. A diluted dose of kelp or seaweed fertilizer also helps prevent stress. Keeping plants protected with row covers for another week will further help them adjust to their new home and give them some protection against fluctuating temperatures.
By following these steps, you'll have a head start on your gardening season. Your plants will be growing steadily in their outdoor garden bed in no time!