Paph pH & Nutrition

[AdeleDS]

I've got a little baby Paph 'Angel Hair' (St. Swithin x Sanderianum). The plant is in a 2-¼ inch pot and its longest leaf is 5.5 cm long and 1.3 cm wide. It seemed to be growing slowly (thought I know they're slow growers), but then I read that Paphs need alkaline water, and I've been giving it my local tap water, which has a pH of 7.7. So I started putting a little baking soda into its water.

And then I read that it needed calcium & magnesium. So I started also putting in a little crushed calcium citrate and a bit of magnesium bisglycinate (because I already had both of those supplements).

Plus, I moved the Paph to a warmer location in my apartment, with a little less light than it had before.

And, it started growing quite nicely; a much larger new leaf grew, and now it is starting another.

Now I see that the my local area is going to increase the pH of my tap water to 8.3/8.5 this year.

My questions: with the increase in water alkalinity, should I stop adding baking soda to the water? And, is the whole calcium/magnesium supplementation a good idea? I also feed it weakly from time to time.

[Ray]

First, understand that high pH and alkalinity are not the same thing.

Second, I disagree that paphs “need” alkaline water. Yes, they need calcium and magnesium, but mine have always done fine at an acidic pH.

Alkalinity is really a measure of buffering capacity- literally the resistance to pH change upon the addition of an acid.

I think a pH in the 8’s is a concern, but I’d want to know what is in the water that is doing that.

[AdeleDS]

Ray - The water source is rain and snowmelt so there isn't much dissolved mineral in the untreated water. There are a couple of different water treatment plants, one adds lime and carbon dioxide and another adds sodium carbonate and carbon dioxide.

"I think a pH in the 8’s is a concern, but I’d want to know what is in the water that is doing that."

[Ray]

The soda ash (sodium carbonate) is added for corrosion control, and is likely to be in the neighborhood of 25 ppm, so probably not worth worrying about.

If it’s still relatively low solids after their additions, it may be that the pH will be lowered by your fertilizer.

[AdeleDS]

Thank you, Ray. I can see I don't understand much about pH and/or alkalinity; I'll have to do some studying!

[Roberta]

For Paphs, some people use crushed eggshells for calcium, or Dolomite lime (calcium and magnesium) as a top dressing for Paphs, especially in areas with pure water. These leach the minerals slowly. Or just use a pure-water formula such as MSU Cal-Mag that includes all of the nutrients. Don't worry about the pH. (Anything above 7 is "alkaline") and even if the water is a bit acidic, soil minerals will tend to raise the pH, it's the condition in the mix that is important not so much what goes in. (That's where the top dressing of calcium-containing materials comes in, too) Don't overthink this...

[AdeleDS]

Thanks, Roberta!

[estación seca]

The large multiflorals aren't at all picky about water nor pH. You would do fine simply using a standard 20-20-20 commercial fertilizer with micronutrients at a very dilute concentration, say 1/8 teaspoon per gallon, at each watering. You will also need a calcium supplement; egg shells don't leach out enough calcium to make any difference at all and they attract fungus gnats.

Here are notes taken in a lecture given by a Paph growing expert:
Paphiopedilums by Brandon Tam, Huntington - DVOS 2017 09 21

[AdeleDS]

⅛ tsp per gallon! Wow, I have been overfeeding. Going by the difference in weight before and after watering, the plant only holds about 1 tablespoon of water at a time.

Thanks for sending me to the Paph notes - very interesting.

[Roberta]

When you water, you should do it so that water runs through the pot. If it's dry it may take a bit of flowing water to get all of the medium wet - and Paphs like to be on the damp side. When you water like that, air is also pulled into the root zone, and any built up fertilizer salts or other crud gets flushed out.

And except for keeping it hydrated, there is no rush for anything... It will need a series of larger pots as it grows (like a child needs new shoes) , but that little plant is probably 10-15 years from blooming size.