Can houseplants left out in cold be saved?

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Q. I forgot a couple of houseplants out on my porch, and they were damaged by the cold. Is there any chance they could come back? They look pretty dead.

A. Their survival depends on a number of factors. Many common houseplants are native to tropical areas. Some are so tender that temperatures less than 50 degrees can cause damage, while others can grow back from the roots even if they sustain severe damage to the top growth. The variety involved is an important consideration.

How long the plants were exposed to freezing temperatures is another factor. A few hours may not be fatal, depending on the plant species, while 12-24 hours or longer is likely to kill the same plants outright. One way to tell is to remove the pot. Healthy roots are firm and white, while those killed by cold are brown and mushy. If they are somewhere in between, take them in and treat them with extra care: They may recover, they may not.

There are a few things you can do to help them recover if they are able. The most likely way to kill the ones that could recover is watering too much. Plants with no top growth use very little water compared with plants growing well with luxuriant foliage. Too much water when they are not using it can cause root rot, which will certainly kill them.

Avoid fertilizing them now or even when they first start growing again. Fertilization pushes new growth that a damaged root system may not be able to support. Most horticulturists recommend withholding fertilizer for houseplants through the winter months anyway, due to the reduced light levels. Plants generally are not putting on a lot of growth through the winter and do not need the extra fertilizer.

Make sure plants are exposed to appropriate light levels. Those that tolerate low light levels will not be helped by exposing them to too much sun.

Q. Why not use whole leaves as mulch? A few months ago I planted small 'China Boy' and 'China Girl' holly plants. We have many trees on our property, and I just left the whole leaves around these plants, thinking that they would protect the small hollies over winter ... No? Should I purchase wood mulch?

A. The problem is whole leaves -- shredded leaves are great. Although it depends on the tree species, whole leaves tend to mat together and repel water. Oak leaves, for example, tend to break down very slowly; they may look the same next spring as they do right now. If they do mat together, they may become water repellent (hydrophobic) and create drought stress symptoms, especially in small plants such as your newly planted hollies.

There is no need to purchase wood chips now. You may eventually want to purchase them to mulch your hollies. Coarse mulch such as large pine bark nuggets or coarse shredded hardwood have less tendency to become water repellent than fine mulch such as miniature bark chips. You could also shred your leaves, regardless of species, and use them for mulch. As they break down, shredded leaves add valuable nutrients to the soil. Your instincts regarding how valuable leaves can be is perfect. After all, no one is out in the woods or meadows spreading 10-10-10.

Leaf mulch should be no more than 3 to 4 inches deep and should not touch the stems of your hollies, or any other plant for that matter.


Send questions to Sandy Feather by e-mail at slf9@psu.edu or by regular mail c/o Penn State Cooperative Extension, 400 N. Lexington Ave., Pittsburgh 15208.


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