Fertilizer question for SW FL, many varieties orchids

[meredog]

I live south of St Pete in FL, and left the Venice Orchid Show with 15 plants. I asked for and received, from a vendor, fertilizer advice, and it's only confused me more, when I try to find the recommended supplies!

First, the haul:

Dendrochilum wenzelii
Phal. amboinensis (H.P. Gift x Hackneau II)
Pot. Dick Smith 'Paradise'
Cattleya walkeriana 'Kenny'
Pot. (Cindy Yamamoto x Owen Holmes) 'Carmela'
Phal. Schilleriana
Angraecum eichlerianum
Dendrobium auriculatum
Angraecum Crestwood 'Tomorrow Star'
Angraecum sesquipedale
Angraecum eichlerianum
Angraecum germinyanum
Angraecum magdalenae
Angraecum leonis
Ren. Monachica x V. Neofalcata 'Shutenno'

Not terribly unreasonable if you don't know that I already have (in spike) an Ang. Crestwood, and yes, I bought 2 Ang. eichlerianum. But each are special in their own way. And yes, I had a thing for Angs on Saturday, well, maybe more than Saturday.

SO.

I asked a vendor who had a lot of B. nodosa crosses about growing conditions, because mine should be blooming profusely based on size. The conversation turned to fertilizer, because I seem to have the right light conditions. (Tho it may need to dry out more).

Basically, he said that my MSU/tap water had to much Mg (I have some orchids turning purple for no apparent reason, outside of my more conscientious fertilizing - they weren't purple when I neglected them), and recommended Southern AG or Better-Gro, 20-20-20. But also recommended epsom salts at low does 1X/month.

1. Isn't epsom salts Mg? So MSU has too much Mg, but then add Mg?
2. I used MSU/tap water in NY for 15 years, under lights and never had issues. but maybe under FL sun, it's an issue? I have learned that NY under lights and FL are very different! even for the same plant!
3. Neither Southern AG or Better-Gro makes a 20-20-20 that I can find,

So what's a girl to do?!

I appreciate FL growing advice and fertilizing advice!

TIA,
Carolyn

[JDT]

My first suggestion would be to have your water tested or if you are on city water you might contact your water department they might be able to get you some info. It is best to see from your water test what it is you have in your water, too much of something or not enough. As to Epson Salts I dose all my orchids with Potassium and Epson every month, using a tablespoon of each per gallon then spray the entire plant. There is a major breeder who suggest that you do this each month, for him always on the first of the month or as close to that as possible. Once you have an idea of what is in your water you can then decide what type of fertilizer to use based on what you might be lacking in your water that our plants needs. I also use a time release fertilizer as you know there are times in Florida we get lots of rain and not always capable of getting out to fertilize well the time release will help. Good luck!


Nice haul at the show, I guess it is correct to call you a orchid addict like the rest of us!

[raybark]

That grower didn't know what he was talking about.

For one, the MSU fertilizer for well or tap water contains no magnesium. The MSU water for RO contains 2% Mg. I use K-Lite, which is a derivative of the MSRU RO formula, and it has 3% Mg.

The Mg content of the RO formula, if used at 125 ppm N biweekly, is roughly equivalent to one teaspoon of Epsom salts per gallon, given monthly. I have given 3x that amount of MgSO4 every other week with no issues.

Unless you overdo the amount, fertilizer isn't going to have that great an impact on your growing. My recommendation is to divide 100 by the number of times you feed per week - the result is the ppm N to use at each feeding. Then, if you divide 8 by the %N of the fertilizer, the result is teaspoons per gallon for 100 ppm N, and you can calculate from there.

Note, if I guessed correctly about where you got the stuff, and it's a liquid, the label actually misrepresents the content, and it really takes one full ounce for 125 ppm N.

Purple color is a "sun tan".

[meredog]

Hi and sincere apologies for the lapse in responding, but I have been busy on this project.

I was using the tap water MSU, so no Mg and no Ca. And it was a granula.

So, on top of no Mg and no Ca, I determined that my baseline TDS is 650-675 (well and faucet), at pH 7.4. Add to that fertilizer, and not only was the TDS enough to kill even me, but at the high pH, some nutrients were no longer available. No wonder I have any orchids still alive!

I have an under sink RO system that I use for all drinking, cooking and pet water, and ice. It reads 50 ppm right now, pH 6.4

My new regimen (after research into the local well water, what other local orchid growers are doing, and RO/hydroponic growers are doing) is:
2 gal RO
1/2 tsp Better Go 20-14-13 (doesn't have Ca and Mg)
1/2 tsp CaliMagic

The result is 250 ppm TDS, pH 6.2

I have a pump sprayer and use this daily to 2-3X week, depending upon the plant.

They have responded spectacularly! Yes, it is spring (here is SW FL), but I think that the change in roots and new growth is because finally they are not drowning in salt water, AND they actually have the proper nutrients!!!

I am going to install a higher capacity outdoor RO system to support the orchids to have. My undersink at 2 gal resevoir can't support my watering needs (I fill buckets constantly throughout the day), and I can hook the new system in off of the softened water. I'm working with my well guy.


Ah chemistry!
Carolyn