by Gene Sumi

Read the Labels

When giving out gardening advice, I usually tell people things that they already know.  This “preaching to the choir” is received well by most people, but there are some who become upset being told something that is “common knowledge”.  What they're forgetting is that common knowledge is not necessarily known to everyone.


I fell into the trap of assuming that everyone probably knows that one should always read labels on things one applies to living things.  I bring this up because this has been a very hot summer, much like last summer.  There have been an unusually large number of days with temperatures well over 90 degrees - and most insecticides, fungicides and herbicides should not be applied when it's over 90°F.  Labels warn against using them when it's that hot outside, for two main reasons.

  • Garden chemicals that are applied as a liquid are diluted with water for distribution.  When sprayed as an aerosol spray in temperatures above 90°F, something hazardous happens - the more volatile chemicals leave the water solution behind and become vapor in the air.  Most of the active chemical in the spray then never reaches the target and the chemical remains in the surrounding air.  This creates an unsafe situation for people, pets, wildlife and plants.
  • In the very hot sun, moisture on the leaves focuses the burning rays of direct sun - much like a magnifying glass - and can burn the leaves very quickly.  Also, some products which are normally safe can do damage when it's very hot.  Many of our organic products contain sulfur, a plant nutrient that's also a natural fungicide and soil acidifier.  But sulfur has a negative quality - it readily absorbs heat, and all products containing sulfur have this warning on their labels.  One of my customers used a sulfur fungicide on her tomato plants on a very hot day and the heat transfer by the sulfur solution the leaves burned every leaf on her plants.

Summer is almost over.  But those 90°+ days may still come before summer’s end.  Please read product labels and follow them, especially if you are using a particular garden product for the first time.

Photo credit.

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