Disinfecting Pots and Trays

Question:  I recently bought bleach to use to disinfect pots and trays.  I brought Ultra Clorox bleach and used it at a one to nine ration as I had done with another bleach.  When I called the Clorox service number, I was told not to use the Ultra product for this purpose.  I wonder what is best to use now.  I also know some people use vinegar.  I have not been able to establish the measurements of a pH level to aim for when using vinegar for disinfecting.  Any comments?

Answer:  At the Violet Barn, we have long used both bleach and vinigar to clean and disinfect pots and trays, and often for leaves and cuttings as well.  We’d always used the “one to nine” ratio, but this question forced us to do a bit more research.  Here’s what we found.

First, “bleach is bleach”.  The active ingredient (sodium hypochlorite) is the same in all bleaches.  However, not all of what youcan buy is of the same strength–not all, or every brand of bleach, is the same.  Ultra Clorox, for example, is simply a more concentrated form of “regular” Clorox.  And your “generic” or “store brand” labels may be even less concentrated.  Look on the label to compare the concentrations of the active ingredient.  This will determine how much bleach you will need to use to effectively disinfect your pots.

Second, what is the recommended dilution?  According to the EPA service bulletin for Clorox, the proper dilution rate for “plant containers in nurseries” (among other things), for the purpose of “plant parasitic nematodes, plant disease-causing fungi and general surface disinfection” is an approximately .85% active ingredient diultion rate.  What does this mean?  Ultra Clorox, for example, contains 6% active ingredient.  When 1 part Ultra Clorox is mixed with 6 parts water, the dilution will be .85% (i.e. 6% divided by 7 total parts).  If your bleach is more dilute, mis with less water.  For example, our store brand bleach has about 3% active ingredient.  We would mix 1 part of this store brand with 2 parts of wter to achieve the proper dilution (i.e. 3% divided by 3.5 total parts).  If your bleach is more concentrated, dilute it more.

What about vinegar?  Vinegar does two things.  First, because it is acidic, and much of the “crust” or residue you find on old, used, pots is alkaline, it works very well to dissolve and clean away these.  We’ll often soak really hard-to-clean pots in a pure (or nearly so) solution of white vinegar to make old pots look new again.  Second, vinegar works well as a disinfectant, especially when used in combination with bleach–it makes the bleach even more effective as a disinfectant!  It’s been found that bleach (which is slightly alkaline) is a much more effective disinfectant when it is acidic (pH 6 to 6.8).  A recommened solution for household use, for example, would be a follows: 1 oz. bleach (6% dilution) added to one gallon water, then add 1 oz. white (5% distilled) vinegar.

Self-Watering Planters

Question:  We received our order of 8 various African violets.  Most of them we potted into self-watering planters.  They are not progressing.  I would appreciate any help you can give.

Answer:  This is likely the single most-asked question we receive.  There is nothing inherently wrong about growing in self-watering, Oyama, or “violet” pots, but when using them you MUST use a VERY porous, light soil mix.  Do NOT use commercially sold “violet soil” (like those found at your garden center, supermarket, or department store) for “violet” pots (for that matter not all “violet” fertilizers are best either).  Putting the word “violet” on the label doesn’t make it good for your violets–in fact, usually worse.  It’s good marketing, and plenty of soil, pots, and fertilizer is sold because of it, but this doesn’t make it correct.

So what kind of soil should be used for self-watering “violet” pots?  One containing at LEAST 50 percent perlite or other relatively non-absorbant material.   Vermiculite, though it does help lighten the soil, still absorbs too much water to be sufficient as an additive.  Select soils using the following rule: the wetter you intend to keep your plant, the more perlite to include in the mix.

Neem Oil for Powdery Mildew

Question:  My sister sent me some “Neem oil” to use for powdery mildew, but I haven’t a clue how to use it.  Could you tell me?

Answer:  “Neem oil” is processed from seeds of the neem tree, native to eastern India and Burma, and is a wonderful product that can be effective as an insecticide, miticide, and fungicide and is safe for home use.  It biodegrades quickly, and exposure to neem oil poses no threat to humans or other higher animals, or to “beneficial” predator insects (only to those who feed on plants).  Though it doesn’t directly kill plant-feeding insects, it does act as an irritant, discouraging them from feeding on the plant.  For this reason, it’s best used regularly as a preventative, or to attack pest problems in their early stages.

We’ve found its best use is as a treatment for powdery mildew, the very fine, white powder that appears on leaves and, sometimes, blossom stems.  Though powdery mildew rarely will kill a plant, it will scar the surface of leaves and lead to short-lived blossoms.  It tends to be a particular problem when there is cool, stagnant, humid air.  Spraying with neem is an easy, immediate, non-toxic solution for dealing with powdery mildew on a large number of plants.  There is minimal damage to open blossoms (a few varieties appear more sensitive), and leaves will look shiny and clean.

We spray with 100% pure neem oil, at a rate of 1 tsp. per quart of water.  To this, add 1/4 tsp. of liquid dish soap, which is need to mix the oil well in the water.  If the oil is very thick, use warm water when mixing.  Spray all plant surfaces generously with a fine mist.  Best of all, it’s not toxic to humans–we don’t use either masks or gloves when using it.  That said, don’t be so careless as to swallow it or spray it into your eyes (not lethal, but not pleasant either).  As for the odor, it smells a lot like sesame oil.  To store neem oil, keep at room temperatures (it thickens if chilled), and shake well before using.

Scarring on Backs of Leaves

Question:  I have brown scarring on the backs of my lower leaves.  Why?

Answer:  This is a question we received by phone.  We didn’t immediately have an answer until he happened to mention that he grew in clay pots, and also wondered why the bottom row of leaves was bent over the pot rims.  The culprits, of course, were the clay pots but, since we hadn’t grown violets in these in nearly 30 years, it didn’t quickly come to mind.  Besides their weight, expense, and difficulty to clean (and keep clean), scarring of the petioles and undersides of leaves can be a problem presented by clay pots.  Being porous, the pot absorbs the water (and whatever is added to it).  The water will evaporated and the pot will dry, but some of the fertilizer remains within the clay, most noticeably on the pot rim–like a ring on a bathtub.  These accumulate over time and can burn, or “scar” the undersides of leaves and their petioles when they come in contact with the pot rim.  This can be more of a problem for African violets, which produce leaves in a flat rosette, than for plants that grow more upright.

A solution for those who prefer to grow violets in clay pots is to create a barrier between the leaves and the pot rim.  One simple solution is to cut thin strips of aluminum foil and fold them over the pot rim.  Using a glue gun, you might also apply a thin bead of glue around the pot rim–or apply a bead of silicone of bath-tub sealant.  Another is to cut thin nylon tubing (like the kind found in tropical fish stores), lengthwise, then secure them to the pot rim.  Some exhibitors use the latter method even with plastic pots, since it helps protect the lower leaves of large showplants from the sharp rims on plastic pots (“rolled”, or rounded, rims are better for this reason).

That said, clay pots are attractive and can make plants look even more so.  Just be aware of their shortcomings and adjust your culture accordingly.  Because they are porous, soil will dry much more quickly than when potted in plastic.  Water is evaporated only from the soil surface with plastic pots, but from soil and pot surface with clay pots.  This means that plants with small root systems, like miniatures, will dry very quickly in clay pots and will need to be watered quite frequently.  Also, very light, porous, soilless mixes that work so well with plastic pots may dry too quickly in clay pots.  A heavier mix that retains more water may work better when using clay pots, unless one plants to keep the plant and soil constantly wet.  Finally, if you want the advantages of plastic pots, but the appearance of clay, you might simply grow in plastic and slip plant and pot into a slightly larger clay pot!

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