Organic Gardening & Farming, Plants, Seasonal Highlights

Hardening Off Seedlings : A How-To Guide

When plants have been growing indoors under warm lights (or in windows), the great outdoors can come as quite a shock. The big bright sun can burn them, the wind can blow their leaves off, and the variable temperatures can stunt their growth. There’s a simple action you can take to prepare your seedlings for the real world. It’s called “hardening off”. Hardening off seedlings is pretty simple once you get the knack of it, but there are some tips that can help the process go much more smoothly.

Pet Your Plants

Starting at the very beginning, as soon as your plants emerge from the potting soil, begin gently petting them every day. This really helps them grow strong and gives them a huge head start when it comes time to harden off. If you haven’t been doing this, that’s okay. Just be extra gentle with your plants as you ease them into outdoor life. Don’t take them out on a windy day, and try to place them in a location that is sheltered from wind for their first few trips outside.

Start Slowly With A Test Run

On the first day you take your plants outside, make it a really easy day for your plants. Choose a non-windy day when the temperature is above 50 degrees Fahrenheit. Water them well, then place them in the shade for one hour. If you notice any signs of distress the next day, give them a day off, then repeat this step. It’s okay if multiple days pass between outings. Spring weather is highly variable, so set your schedule by the weather rather than the calendar. Keep repeating this step until your plants can handle it easily, with no signs of stress.

Plant Training Regimen

This process is sort of like a fitness regimen for your plants. They build “muscle” slowly throughout this process until they’re ready for the marathon of outdoor life. After the test run, I move my plants to a slightly less protected area: the south side of my house. I provide partial shade for them by staggering my mesh patio chairs around them. Don’t go out and buy patio chairs just for this. Do what I did, and get creative with the location and materials you have on hand. A tree would also work well!

On the first day, leave your plants outside for one hour. Second day: 2 hours. Third Day: 3 hours. Keep going through Day 8 (8 hours).

Trays of growing seedlings hardening off underneath patio chairs

Let Them Fly

Starting on day 9, they should be ready to stay outside all the time, as long as the weather stays reasonably nice. Proceed with caution, using all your senses to monitor their well being and checking on them frequently for any signs of stress. Keep them in a semi-protected area for another couple of days, gradually moving them away from the shade until they seem strong enough to go out to the garden. If the weather has sufficiently warmed, you can plant them at that time. Otherwise, leave them in their pots until the time is right so you reserve the option to bring them back inside if needed.

A group of potted plants including white sage, rosemary, lavender, bay, turmeric, and a variety of citrus trees.

Older Perennial Plants

Older potted plants that spent last summer outside and simply came in for the winter will generally be more robust than baby seedlings that have never seen the sun. However, they still need to be gently acclimated to outdoor conditions. Some plants are more delicate than others. My citrus trees need to be placed in a shady location and gradually moved into the sun over a period of a few days. I bring them back inside if the weather gets cold or if a big storm is on the horizon, but they don’t need to be brought in and out every day for 8 days. Rosemary, Bay, and Lavender respond well to a similar treatment. However, my White Sage plant is very delicate. It requires the full hardening off process, and a reverse “softening up” process in the fall. Over time, you’ll learn what each of your houseplants prefers. If you make slow, careful changes and you pay attention, your plants will show you what they need. And if you make a mistake, learn from it, and take notes. You might make a new mistake, but you won’t make the same mistake again.

The Fun Part

Once your plants are planted in the garden, the real fun can begin! Since you’ve treated them so well and given them every care, they now have the best chance to flourish. I wish you a bountiful growing season!

Related Articles

To All The New Gardeners
Becoming A Garden Superhero: 6 Skills To Cultivate For A More Resilient Garden
Growing In Place : How To Spot Bad Garden Advice Before It Spoils Your Harvest
How To Choose A Garden Tool That Will Last A Lifetime: The Top 5 Questions to Ask Before Buying