GardenBanter.co.uk - View Single Post - Micro-nutrients???

26-05-2004, 02:05 PM

Hello

(solo_voyager) wrote in message . com...
I began using this fertilizer concoction early in 2000 after reading
an article about windowsill growing in the Dec 1999 'Orchids'. The
recommendation was to use a bloom booster year around. It has worked
well for me with no apparent problems until this season.
I began to suspect deficiencies or toxicity when the only info I could
find for yellowing of middle to older leaves seemed to shotgun trace
mineral shortages. Although, some potential excesses were listed.

High P is famous for inducing at least a severe Zn deficiency,
sometimes a triple Zn/Mn/Fe deficiency, very difficult to diagnose
visually. Zinc is essential to orchids, and most genus have Zn amounts
( foliar analysis) much higher than iron. Mn is usually pretty high
too.

1. To use a bloom booster formulation year-round to help simplify my
in-home growing of cool-dry-rest Den.'s that require a variety of
tweaked conditions to make them all happy enough to bloom.

The newer fertilizers with Calcium and Magnesium, usually coupled with
an high NO3 content induce a lot of micronutrient deficiencies. I can
see them in the analysis but they are not yet ver obvious visually...
Expect surprises similar to the CHC story, haydite, rockwhool and the
like in the coming years with those fertilizers.

2. The crystalline fertilizer was chosen because of it's 100% useable
Nitrogen content. Plus, some micro-nutrients were available from it.

Crystalline fertilizers are very difficult to store properly.
Micronutrients are usually gone by 3/4 to whole after only a year of
storage... Try to make a 30 x concentrate of your powdered fertilizer.
Usually there will be a lot of various crystals that will not
dissolve, easy to spot.

This has worked well for me since early 2000. It has been only this
growing season that the problem has begun to show severely on several
plants. What I am now considering to be the indicator for this is a
plant I purchased in 2000, a D. falconeri.
The vendor didn't want to sell it to me at that time because he had
had a "bad water" problem with them and they were still recovering
from it. I brow-beat him into selling me one anyway. It has grown well
for me until this season. It is now one of those plagued with
yellowing and die-back from the tips of the older leaves.

Quite common too... I have many orchid growers customers, not in the
USA.
Many of them are at a prehistoric age of growing orchids. I am sure
they would win at the lottery with the luck they have ! Most are still
trying to "improve" the growth of their plants, sometimes it works
sometimes not. Last people to talk is right. Sometimes it is possible
to undo their changes, sometimes not...

Substrate and macronutrient fertilizers needs at least a year, more
commonly 2 years to show any large problem. This group includes iron
too.

Micronutrients... it depends. Zinc and manganese is common today,
because many growers abandoned the old mancozeb fungicide several
years ago. Orchids have a quite high Zn content usually, and this
content slowly drops over the years if not properly supplied. Count
between 2 and 6 years for a plant to start funny yellow striping on
the leaves, and many new small growths on the plant.

Molybdenum deficiency is very common with the use of high NO3
fertilizers, but not yet a lot of obvious symptoms. Some plants here
and there in a crop are grayish, dull green, or yellowish. Usually
classified by the grower as "weak plants"...
It is translocatable, so expect a burst of weird looking plants in the
years to come. It is hard to diagnose, as the levels can be higher
than the recommended standard and still be deficient. NO3 (not total
N) foliar analysis is the only way to assess molybdenum deficiency.

Many growers are incredibly lucky. They will treat "leaf spot" with
mancozeb, and provide an additionnal Zn/Mn shot valid for a couple of
months or more, saving their plants. Sometimes they will forget to
correct the pH of the fertilizer once. Enough for the plant to restore
a part of its boron supply in an alkaline substrate. And so on...

Now, ask most growers. "Can you show me your foliar analysis ?" Have
you done any substrate analysis". A geranium grower will tell you
"yes". An orchid grower usually "wazzat ?"

Even a chlorosis of the new growth must be diagnosed by a lab... iron
deficiency exists, still many orchids suffer from iron toxicity, with
levels over 800-1000. This is what killed many plants grown in
haydite.

Iron-EDTA will sometimes exchange the iron against manganese (ans
zinc), and plants may improve with its use. This does not means that
iron was the culprit.

I am going to reassess my fertilizer regimen, lower the phosphoric
acid content and not worry about micro-nutrients. In the meantime I'll
do a thorough leaching of the pots and mounts to clear them out, then
take another run at it.

If you underfeed and use fish emulsion with an high Na content, you
may have a sodium toxicity. Dendrobiums have proven to be able to
replace a part of their potassium by sodium, during a potassium
shortage...

Basic :

- Mix 1 part of substrate to 1 and an half part of water, by weight.
Let stand overnight. Test the pH and EC. Optimum pH (according to
foliar analysis, and comprising all possible deficiencies and
toxicities of micronutrients) for SPENT medium is 5.7 for most hybrids
of most common orchid genus... Optimupm extract EC is over 400 and
under 1000 ( depending on the genus).
- Add some dolomitic limestone to raise the pH up to 6.

- Use a 20-20-20 (best one is the "20-20-20 Florida Special" from
Peters/Scotts) at the microsiemens rates given above, pH 5.7, no
more...
- pH of the substrate will drop using this fertilizer. Check the water
running out of the pot after a watering every other month. Too low,
add lime. Too high, use epsom salts once.

- Use from time to time a 15-5-15 CalMag or similar, but do not overdo
it. Once every moth to once every other month is more than enough.
Correct the pH to 5.7 too.

- You may use calcium nitrate and magnesium sulfate monthly , but I
have to know that those are more in excess than deficiency amonghst
the several dozen foliar and substrate samples I am doing yearly.
Magnesium sulfate - epsom salts - serves to supply SO4-, lacking in
many culture, and lowering the pH, therefore making micronutrients
available. Otherwise, the magnesium itself has no effet. IF you do not
believe it, use magnesium nitrate instead...

Good luck with your plants.