Young seedlings when purchased from the local nursery or Garden centre have generally been grown under cover not being subject to extremes of environmental changes. Nurseries will put plants through what is known as a hardening off period but this is not like the environment a plant goes into when it is purchased and does not account for shock associated with transplanting.
To protect plants, covers are usually placed over each one individually until they have doubled or tripled in size. This is a good indication that the plant has established itself in its new environment and is likely to survive with the extremes outside of its protective surrounds. Plants that are not protected can suffer from stress associated with cold, wind, animals and insect pests.
What to use to protect small plants and seedlings?
Over the years I have used several different protective coverings over my vegetable seedlings. I have used anything from inverted buckets to old cans and tins. The downside of these types of coverings is the need to remove them every morning to let the light in and replace them before heavy winds or at night. These are not the most ideal options but they work when better options are temporarily not available.
The best covers for seedlings I have used are clear plastic soft drink/soda bottles that have been cut in half. Both the top and bottom of these bottles can be used. For the first few days the bottles can be placed over without any breathing holes. After a few days remove the lid from the top half of the bottle and place a couple of holes in the bottom half.
The second best option is to use plastic bread bags over 3 or 4 stakes or sticks which are placed around each plant. These bags can be lifted up from the base of the sticks a little at a time over a period of a couple of weeks until they are removed altogether.
What about buying protective plant surrounds from the nursery, garden centre or store?
There are commercially available plant covers on the market. These range from plastic bags like those used around trees in plantations to small plastic covers with built in venting systems. There are also mini tunnel style coverings designed for use over rows of plants. These work well but also take energy and chemicals to produce. If you do not have any recycled options available such as those listed above, buying these types of coverings may be an option for you.
Regardless of what you use for coverings it is important to monitor the temperature around the plant to prevent heat stress or major water loss.