Issue: December 13, 2003

Apartment too hot to flower Thanksgiving cactus

Question:

I have a Thanksgiving cactus that my parents gave me 2 years ago. The flowers were beautiful when it arrived around Thanksgiving that year, but since then it hasn't formed any flower buds. I live in an apartment that is kept quite warm. The temperature is between 70-77 degrees most of the time. The environment is very dry, but the room is bright. I have no control over the heating system. Is that the reason why my cactus can't form any buds? What should I do about it? Thank you very much! L. Tsien via Internet

Answer:

The maintenance of a high temperature may be part of the problem. The length of the uninterrupted dark period at night is another factor. In a small apartment, it may be that the lights in the apartment prevent the production of flower buds.

Is it possible to move the plant into a dark closet (which is not entered at night) for a period of 14 hours each night? Each day it should be returned to a brightly lighted location. This may be sufficient treatment to encourage flowering. Another method of providing the darkness is to cover the plant with a black cloth or black plastic bag during the 14-hour dark period. Do not leave it covered when sunlight shines directly on the plastic bag because this will create enough heat to injure the plant.

If long nights are not sufficient to induce flowering, it may be possible to "trap" a little cold air adjacent to the window. A plastic sheet separating the plant from the room (creating a small compartment next to the window) may trap enough coolness next to the plant. During the night you will still need to provide darkness using a black covering. During the day, when you remove the black covering, you must also release the plastic sheet that forms the barrier between the plant and the room (once again to prevent overheating).

I once had a Christmas cactus that flowered only on one stem that was touching the glass of a window. This one stem was cooled sufficiently by the cold outside the window so that it flowered even though there was light interrupting the night period.

The effort necessary to induce flowering is greater under the conditions in which you are growing the Thanksgiving cactus, but the flowers are worth the effort. This is especially true because the plant was a gift from your parents.

Small insects in African violet potting soil

Question:

What are those little bugs I see in my plants that are growing in a peat-lite potting soil? They don't fly or jump. They are very small, and the only time I see them is if I look closely when I water the plants. What can I drench with that won't kill my African violets? Dblatt aol.com

Answer:

You are probably describing fungus gnats. As adults, they can fly and will be attracted to windows and electric lamps. Their larvae feed on the fungus in the potting soil and, to some extent, on the plant roots. They may be captured by yellow sticky traps placed in brightly lighted locations. There are products made to drench the potting soil as you asked. They contain Bacillus thuringiensis subsp. israelensis, a bacterial toxin that will not harm you or most plants. Read, understand, and follow the label directions before purchasing and applying any pest control product.

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For more gardening information, visit the NMSU Extension Horticulture page: desertblooms@nmsu.edu.

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, office: 505-865-7340, ext. 113.