Issue: February 3, 2001

• Ficus tree frozen
• Does smoke hurt plants?

Ficus tree frozen

I have a Ficus tree growing in a protected area where it almost never freezes. I usually cover it up when it's going to freeze, but one night it froze when I didn't cover it up. Now the leaves have started to fall off, turn yellow, some have round spots (look like burn spots), and some of the limbs have turned completely brown and died. What do I need to do to keep the tree alive if possible? Thanks.Tamme Johnson (via internet)

This year has been a return to the cold winters. There will be a lot of plants, some of which are not houseplants, that have suffered freeze damage, so the advice that follows applies to them as well.

The loss of leaves and dieback of the stem are good evidence that the tree was injured. However, the degree of injury is not yet apparent and may not fully be revealed for a few months. You can trim off any dead wood, those branches and twigs that dry and become brittle and those that do not have a green layer below the bark or epidermal layer when scratched lightly. If the twig is healthy, a light scratch by the thumbnail will reveal a green layer. If the layer below the bark is black or brown, the branch is dead and can be trimmed.

Some branches that lost leaves may develop new leaves if the injury was limited to the leaves. So, wait before pruning too severely. It would be wise to wait before doing major pruning if you want to reduce the size of the tree. You don't want to remove healthy wood leaving damaged branches behind. Remember, it is okay to prune dead and dying wood at any time of the year.

It is also important to water properly now. Since the leaf surface is reduced, the tree will use somewhat less water until new leaves are formed. Be careful not to overwater. You should also reduce fertilization during this time. Application of a diluted (more diluted than usual) liquid houseplant fertilizer once a month should be adequate. The same advice is appropriate for freeze-damaged trees in the landscape as well.

Does smoke hurt plants?

Does smoke affect growth of plants? Tovias (via internet)

This is an interesting question relevant to houseplants (and outdoor plants to a degree). However, you did not give me a complete return e-mail address (this happens often), so I can only answer in this manner.

Plants can be affected in both a positive and negative manner by smoke.

Smoke, produced by combustion of some material, means that there is increased carbon dioxide over a limited area. This is good for the plants and can increase their growth if there is sufficient light.

The smoke particles that we see, however, are particulate pollution which can coat the leaf surface, reducing photosynthesis. These particulates can also clog stomatal pores, reducing gas exchange in the leaf. These effects are bad for plants. Cigarette smoke, and some other smokes, also contain tar which can clog stomatal pores.

Particulate pollution in smoke can be harmful to humans as well. Plants can be used to cleanse the air. As we all learn in school, plants need carbon dioxide (which we exhale when we breath) and produce oxygen (which we need). That's good. Plants can also cleanse particulate and chemical pollutants from the air, protecting our health. Plants with fuzzy leaves are most efficient at cleansing particulates from the air.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!