"Hardening" is the process of gradually introducing your seedlings to direct sunlight, wind, and fluctuating temperatures. If your plants have grown up in a sunny window, they can't handle a full day of direct sunlight. They need to be introduced to the outdoors a few hours at a time.
Many new gardeners grow beautiful seedlings indoors, only to watch them die in one or two days when they move them outside. Usually, they have no idea why the plants they carefully nurtured over the past two months have suddenly lost the will to live. The problem is that no one ever told them new seedlings need to be "hardened."
How to "harden" your seedlings without a pop-up greenhouse 1. Begin the hardening process when there are a few cloudy but warm days in the forecast. This way, you can leave them out all day because there won't be any direct sun. 2. If there is direct sun, only leave your seedlings outside for one hour on day one, two hours on day two, then three hours, then four, then all day. 3. Do not leave your plants out overnight for the first week. 4. Do not leave plants out overnight if it's going to drop below 45 degrees. 5. Do not leave them out on a very windy day unless they are protected from the wind.
How to "harden" your seedlings with a pop-up greenhouse 1. Put them in the greenhouse. 2. Leave them there. 3. Open the vents on sunny days so that they won't overheat: If you don't vent your greenhouse, you'll fry them.
I have to admit that I love my pop-up greenhouses. My mother bought them for me on sale for $25 about three years ago and they've stood the test of time. I have raised and hardened thousands of seedlings in them.
The ones that I use are from flowerhouse. They are made of strong, translucent plastic that creates diffuse light (ideal for raising seedlings). They also have vents on both sides, they break down and set up easily, and they can be stored in my garage in a little bag on a shelf.
Here's a link to the greenhouse that I use:
My pop-up greenhouse has vents, creates translucent light, and can be opened from both sides. Mom got it for me on sale for $25 (she's a bargain hunter).
I moved my tomato plants to the pop-up greenhouse today. I will leave them out day and night unless it goes below 30 degrees overnight.