An easy way to protect tender seedlings in early spring is to cover them with a cloche-a glass or plastic structure that protects plants from fluctuating temperatures and inclement weather. You can purchase cloches at nurseries, but a less expensive option is to make one out of a recycled 2-liter plastic bottle. Here's how to do it.
Take an empty 2-liter soda bottle. Remove the cap and rinse out any sticky soda residue that may be inside. Then, peel off the label. It's important to use a clear bottle as opposed to a green one, because the clear plastic lets in the maximum amount of light.
Using the serrated utility knife, cut off the bottom 3 inches of the bottle. Discard the bottom.
Out in the garden, place the cloche around the seedling you wish to protect. Center the cloche over the seedling and then press it down into the soil to prevent it from tipping over.
The cloche will act like a mini green house by absorbing energy from the sunlight and warming up the air around the plant. During the day, you may wish to keep the bottle uncapped so some of the warm air inside of it can escape. At night, you can screw the cap on to hold the warm air inside.
Remove the cloche when the seedling begins to grow into the upper part of the bottle.
Temperatures can quickly rise inside the cloche; if a very sunny day is predicted, you may want to take the cloche off in the morning to prevent the seedling from overheating in the daytime.