In the Garden:
A PVC frame covered in plastic with a little supplemental heat from light bulbs can keep these plumeria and hibiscus alive through a few mild winter freezes.
Extending the Zone for Tender Plants
Here in the lower south our winters are but a brief interruption in our long growing season. However, a few really cold snaps can put an end to an otherwise nice cool-season garden. There are a number of cold-tender plants, such as fig trees, yellow bells (Tecoma stans), Satsuma oranges, and kumquats, that could be grown outdoors if we could just get them through a few brief cold snaps.
In fact, there are a number of ways to protect a semi-hardy plant on a night when temperatures drop into the low 20s or teens. Here are a few tips and techniques to cheat on winter and maintain a few plants that are a zone too far north for their liking.
Row Cover Fabric
Spunbound polyester fabrics come in several weights. The lighter-weight products (approximately .6 oz. per square yard) are suitable for protecting plants from insects, but not very helpful when frosts threaten. Heavier-weight fabrics (around 1.2 oz. or more per square yard) can protect plants against frosts and light freezes. They will provide a few degrees of protection by holding the heat of the earth beneath them and around the underlying plants.
When practical, the fabrics should be removed during the day to allow the sun to heat the soil and plants. Then, in late afternoon or early evening, recover the plants for overnight protection. These fabrics are most helpful in protecting low-growing plants, such as strawberries and vegetables. Large plants like fruit trees and vines may be too large to cover easily and effectively.
For more protection, use blankets or plastic to cover the plants. These do a better job of holding in the warm air. Plastic can "burn" plants where it touches the foliage on a freezing night, but this is a small price to pay for protecting the entire plant from freeze damage.
Prized plants that lack cold hardiness, such as small citrus trees, can be covered for some protection, provided that the cover extends to the ground so it will trap rising soil heat. To simply wrap a plant like a "landscape lollipop" will do little good.
Sections of PVC pipe can be used to make a box or frame around a tender shrub or young tree. Cover the frame with inexpensive, clear plastic to make a mini greenhouse. I use a 6-mil plastic, which is readily available at most home supply stores. It will last through the winter season. This box needs to be anchored to hold it down when a "blue norther" comes blasting through. I have used metal posts driven into the ground or cinder blocks tied to the base through holes drilled in the PVC.
The PVC-framed box is fine for protecting against a moderately cold night, but for added protection you can use a source of heat inside the cover. Light bulbs or a string of the large outdoor Christmas lights can provide enough heat to give a few more degrees of protection. Check cords for bare areas, and don't allow the hot bulbs to contact plant stems or foliage. Place the lights near the ground or low in the plant canopy because the heat from the bulbs will rise up through the canopy.
A thick layer of mulch will protect the tender crown of a tender plant during our brief winter cold snaps. I like to use a thick layer of hay or leaves. Innovative gardeners have even made a temporary cold frame by placing four bales of hay against each other to form a box. Then they fill the interior with hay or leaves.
A ring of wire mesh can encircle a fig bush and be filled with lots of leaves as an alternative technique that ends up looking like a large compost bin. The wire is removed in spring, and the leaves are spread around the area as a nice surface mulch.
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