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Water Salt Residues


I was present during the judging at the recent aroid show in Miami.
Being a neophyte regarding the usual showy aroid types, my main
activity was tagging along and listening to the opinions of those with

One thing I did notice, however, was the presence of residues of water
salts on the leaves of several of the entries. The salt formed
patterns, such as streaks and drips, that proved that the source was
originally water. Often a plant would have a beautiful, pristine leaf
at the center surrounded by salty older leaves. Does this bother
anyone but me? My feeling is that whitish salt films detract from the
appeal of an otherwise well-grown plant. Were I in charge of a formal
judging I would subtract points for water salt residues.

It might also be the case that the accumulation of water salts on
leaves could adversely affect leaf longevity or even plant health

I know water salts pretty well. In most areas, water from the tap,
lakes, streams, or wells contain dissolved minerals. When such water
is evaporated it will leave behind a residue according to the
concentration of the minerals in the water source. Once the water
dries it is very difficult to re-dissolve the salts. It might seem
that a salt that is once dissolved in water can be easily redissolved
and rinsed away, but such is not the case. Some may dissolve again,
but much will not. If the rinse water is acidified, as with the
addition of some vinegar, much or all the salts can be redissolved;
but acidification runs the risk of damaging the plant tissue.

The best alternative is to prevent water residues from drying in place
on leaf surfaces in the first place. Three possibilities are: 1) using
deionized water (or distilled water or reverse-osmosis water – R.O.)
for sprinkling or humidificaton; 2) following a tap water sprinkling
or humidification with a deionized water rinse, flushing away the
salts before they dry; and 3) watering and humidifying solely from the
planting medium or other nearby evaporative moisture sources, avoiding
water contact with the leaf surfaces.

In some situations it might be possible to utilize rain water as a
substitute for artificially deionized water. Similarly, you may live
in an area with unusually clean well or tap water. In any case, it is
a simple matter to make a quick check of your water quality. First,
get a piece of clean window glass. Clean it thoroughly so it is mirror
clean. Next, lay it on a horizontal surface and place single droplets
of your water in an array of, say, 3 x 3 and allow the water to
evaporate to dryness. Then examine the footprints where the original
droplets rested. The amount of visible residues is a direct measure of
what you will leave behind on a leaf surface for the same size

Of course, it is also the case that water salts will accumulate in the
substrate over time, especially in containers where evaporation is
high. Horticulturists will recognize how unsightly salt “calc”
accumulates on pot soil surfaces and the pot edges as time goes on.
These are due to water salts (augmented with fertilizer) and indicate
it’s time to repot. Repotting is required more frequently for
salt-intolerant plants. Salt intolerance is the rule for most of our
favorite species.

Back to my original point: Do others have ideas about salt residues
for judged show plants?

Ted Held
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