For many years the only water available to me for my orchids was too
salty and getting even worse from salt water intrusion into the aquifer.
A concrete cistern was constructed to collect and hold rainwater.
Rainwater contains almost no dissolved solids, so you can imagine my
surprise when an analysis of my water showed high levels of dissolved
solids. Concrete cisterns are made of lime and some of that is lost to
the water through leaching.
Fortunately, other than making the water
basic and leaving a white film on leaves, there was never a problem
using this water. My orchids thrived with this calcium laden rainwater.
After 4 or 5 years, water from the cistern was just slightly higher in
solids than rainwater.
I often recommend keeping a log book indicating when various pesticides
were sprayed, fertilizers used, etc. This is important in diagnosing the
cause of problems that arise from time to time. An orchid growing friend
had been using some of the bench in my greenhouse when I installed the
cistern and was amazed at the incredible growth of his paphs under my
care. After obtaining a few paphs of my own and studying the natural
habitat it was clear why paphs had grown so well. It was the extra
calcium and magnesium leaching from my cistern. To compensate for the
slow change in water as my cistern reached equilibrium, I began adding
dolomite lime to pots containing paphs and they thrived. I also began
using Peters Cal Mag, which provided even more calcium and magnesium
each time fertilizer was applied. My cattleyas and other orchids thrived
under these conditions except in the summer when I would experience new
growths that rotted. I would also lose seed pods from rot.
Every orchid hobbyist knows that moving to a new greenhouse requires a
reexamination of culture, and my move to Florida four years ago has been
no exception. The one big surprise was an issue that had occurred
before, always in the summer, that was never resolved to my
satisfaction. During very warm summers there would be the occasional
rotting of new growths on cattleyas as well as on new leaves of
phalaenopsis. Most surprising was that the issue occurred on both
species and hybrids that should have been fine under high heat and
temperatures based on their countries of origin. On these occasions,
various anti-bacterial and anti-fungal agents were used.
Based on the premise that most horticultural issues are caused by
culture, various attempts were made including altering fertilizers,
increasing air movements, etc, with no real clear success. The problem
typically disappeared once temperatures cooled in fall. Most frustrating
was the loss of countless seed pods of some potentially great hybrids.
They would begin rotting from the tip and the rot would eventually
progress, destroying the seed pod.
If you have ever grown tomatoes, you have likely encountered what I have
finally discovered as the cause of this problem. Orchids are
cold-blooded and when it gets warm they are capable of growing at a very
fast rate. To do this, they must take up nutrients at an accelerated
rate, too. Calcium and magnesium are required for proper cell
development in new leaves and other tissues, e.g. seed pods.
During summer’s high temperatures, many orchid hobbyists report loss of
new leaves especially when growing outdoors. Heavy rains flush
nutrients, especially calcium and magnesium, from media, and at the same
time the high temperatures and humidity foster very rapid growth. It did
not occur to me to increase the calcium and magnesium content of the
water I am now using since it comes from a limestone aquifer and is
loaded with minerals, including calcium. My fertilizer now is fish
emulsion instead of the cal-mag fertilizer I have used in the past.
Essentially, I am now providing more of the essential growth nutrients,
mainly nitrogen, but not enough calcium for my orchids in this high
growth time of the year.
When I first realized what was causing the increased loss of new growths
and seed pods, I hand spread dolomite limestone powder all over the
plants in the greenhouse. My orchids looked like it had snowed. I also
placed a couple of pounds in the reservoir from which my Dosatron draws
water after I have applied fertilizer. Within a week, there ceased to be
an issue of rots despite the highest summer temperatures of the year.
Even some of what I consider intermediate temperature orchids have
responded to the extra calcium and magnesium by growing extremely well
in the heat. Most orchid growing advice suggests acidifying water.
Adding dolomite raises pH, but has not had any negative effects so far.
I still flush regularly and fertilize with fish emulsion and this likely
keeps the pH of the medium at the right level for growth.