How to Harden Off Seedlings

When you start your own seeds, it typically involves beginning them indoors where the climate is controlled and the young seedlings are protected. Then, when they’re strong enough and the weather is right, you transplant them outside (anyone who’s ever sent kids off to college can relate).

But in between the sheltered indoor and the real-world outdoor environments, there’s a middle chapter where you “harden off” or prepare your little seedlings for their new life outside. Kate Copsey walks us through it in her book, New York and New Jersey Month-by-Month Gardening.


How to Harden Off Seedlings

Young plants have spent the early part of their lives in a warm, still atmosphere. Acclimating seedlings to wind and direct sun is something that takes a few days. This adjustment is call “hardening off.”

  1. Pick a calm day to take the seedling tray outdoors for the first time.
  2. Place the tray in the shade and bring it back in after about four hours.
  3. Repeat this on Day 2.
  4. On Day 3, leave the seedlings out all day and return them in the evening.
  5. By Day 4, you can introduce seedlings to direct sun for three to four hours and then return them to shade.
  6. On days 5 and 6, leave seedlings in full sun for a longer time (four to six hours).
  7. By Day 7, seedlings should be able to stay outside in the sun all day and night (check the temperatures). While outdoors, seedlings dry out faster, so continue to monitor the water level and protect them from storms and high winds.

Buy from an Online Retailer





Gardeners living in New York or New Jersey need this easy-to-use guide for year-round plant care!

If you’re a passionate gardener and a resident of New York or New Jersey, there’s a book you must acquire for your bookshelf: New York & New Jersey Month-by-Month Gardening. Falling in line with the Cool Springs Press gardening series, this book provides monthly gardening advice, written just for New York and New Jersey gardeners.

This gardeners’ guide is organized according to calendar month–January through December. Each month is divided into the following categories: planning, planting, caring for plants, watering, fertilizing, and problem solving. Within those categories, gardeners will find the major plant groups (annuals, edibles, perennials, trees, lawn, and shrubs) covered in detail. Learn the proper time to plant your favorite bulbs and edibles, and find out how to plant bare-root trees. From planting perennials to coming up with a strategy for pest management, New York & New Jersey Month-by-Month Gardening guides readers through every major question that crops up.

With essential how-to information organized into helpful sidebars as well as step-by-step photos to illustrate technique, this book is a veritable road map for a year’s worth of gardening tasks in this diverse region. Roll up your sleeves, gardeners, and prepare to get dirty!

Kate Copsey has been a certified Master Gardener since 1988. Although she has lived all over the country, gardening in a variety of zones and climates, Copsey has now put down her roots in Jackson, New Jersey, where she maintains vegetable and perennial gardens.Copsey is a popular gardening speaker in the Tri-State area of New York, New Jersey, and Connecticut. She actively seeks out opportunities to educate the public about best growing practices. She also writes for magazines and websites, including the Atlee Burpee & Co., where she is the editor for regional writing. For several years, Copsey hosted the weekly garden radio show America’s Homegrown Veggie Show, and she now hosts its sister program, Master Gardener Hour.