Algae in Water

Question:  As we like to travel, we have set up large trays, 2″ deep, with grids, upon which sit the plants with wicks dipping into the water.  This method has been very successful.  However, I have one problem–a spectacular array of algae.  Is there anything I can put in the water to retard the growth of the algae, and still be harmless to the plants?

Answer:  Bright light and water mean algae.  Using dark-colored trays will help, since less light is reflected off of the tray.  We used to have the same problem on the blankets that we use as capillary matting for many of our violets, made worse by the fact that cheap acrylic blankets seemingly can be found only in lighter colors.  Thos blankets could get real ugly, real fast, even when cleaned regularly.  We’ve never found the algae to be harmful to violets, even when the blankets were greener than the plants sitting upon them.

To remedy this, we began adding Physan 20 to the water used to wet the blankets.  Not much is needed, far less than the recommended dilution.  In fact, we add only about 1/2 to 3/4 tsp. per gallon of water, once every three weeks.  Doing this, we’ve had virtually no evidence of algae since, and there’s seemingly no ill effect on the violets.  In addition, the product is relatively safe to use and has a not unpleasant soap-like smell.  For those that wick-water, it works just as well in keeping reservoirs free of algae. 

Yellowish Center Growth

Question:  Seemingly overnight, two of my repotted plants leaves have turned a light yellowish-green in the center growth.

Answer:  When we got this question, we immediately thought back to one of our local club meetings the week before.  A member brought in a “problem plant”, whose outer rows of leaves were its usual shade of green, but whose center rows were nearly yellow-green.  Just by chance, this was “soil test” night, where members can have the pH of their soil tested.  Her soil tested at a pH of 5.4, very acidic, and far below the optimum (about 6.8, where 7.0 is neutral).  When this was pointed out to her, she then told us that she had recently repotted a number of plants into a commercially sold soil mix bought at a local department store.  There couldn’t have been a better example of the consequences of too low (or high) a pH if we had planned such a a program!

When pH is too low (acid) or too high (alkaline), many of the nutrients become “locked up” and can’t be used by the plant.  Even with proper fertilization, plant roots are unable to take-up important nutrients and, simply put, the plant “starves”.  The result is the yellowish foliage growth that appeared once the overly-acid soil mix was used by this grower.  The consequence of too high a pH can be the same.  This is a problem for those of us with very hard, alkaline, water.  For example, our water usually tests at a pH of 7.4 or higher.  To correct for this, we simply add enough vinegar so that the pH is as close to neutral (7.0) as possible.  For our showplants, we use “distilled” water that we collect from our dehumidifier (in the winter) or our air conditioner (in the summer).

Acidic water is a less-common problem.  Rain water can be quite acidic for some.  One product that we know of is “pH up” a product of Dyna-Gro.  This is a fertilizer supplement (a formula of 0-0-8) that raises water pH.  A supplement of “pH down” is also available (a 1-5-0 formula) and we have heard positive comments–if vinegar isn’t for you.  We have also heard of some growers using products available at tropical fish stores to correct for this.


Question:  I have some violets as well as a few orchids.  My problem is aphids, which I think came in on some mini roses from a local nursery.  I’d like to get some more violets, but I’d like to get rid of this problem first.

Answer:  Aphids aren’t usually a common problem in violets, though they have been known to appear in a collection on a rare occasion, usually when brought in on another plant.  They are usually light green, sometimes black, and have soft, pear-shaped bodies that are easily visible to the naked eye.  They usually can be seen on the undersides of leaves or on blossom stems, where the plant tissue is softer and more vulnerable.  Because they are easily visible, they can usually be easily eliminated with quick treatment of the affected plants.

Only twice (in over 25 years) have we found aphids in our violet collection.  In one instance, they came in on some newly acquired orchids and were quickly eliminated by spraying the affected plants with Knox-Outat the recommended dilution.  One thorough spraying did the trick.  There are a number of insecticides that can be effective on aphids–malathion, diazanon, or many pyrethrin spays.  As always with such chemicals,read the label, and follow all of the usual precautions to protect yourself from exposure.  In the second instance, we found large numbers of aphids on a number of Streptocarpus plants that we had purchased at a show.  In this case, the numbers were too many, and the plants not valuable enough, so we simply tossed all of the affected plants into the compost pile.  They could have been saved, but doing so wasn’t worth the time and wasn’t worth the risk to our health.

Leaves Curling Downwards on African Violet

Question:  The leaves of my violets are curling downward and center growth appears very crowded.  There is no evidence of mite, and I suspect it may be the cold temperature in my growing area.

Answer:  Yes, the problem is likely the cold growing environment.  When grown in very cool conditions, many violets will exhibit symptoms similar to cyclamen mites.  Center growth will be very tight or bunched, leaves will be more “hairy”, and growth will be stunted.  So before discarding any plants or using toxic chemicals, ask yourself if cold temperatures may be the cause.

How cold is too cold?  As with many things, this depends partly upon the variety being grown.  For example, many of the species Saintpaulia will tolerate temperatures much lower than will the modern hybrids.  We find that most varieties will tolerate temperatures as low as 60f degrees.  They will grow much slower, but otherwise look healthy.  Any colder than this, and most varieties simply stop growing and exhibit many of the symptoms described here. 

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