Should I add limestone, crushed coral, etc. to my bark mix?

[varda.elentari]

I'm planning to repot a Paph and a Phrag (unknown varieties) that have been growing in sphagnum to bark mix. Those of you who grow these two genera in bark, do you add limestone, crushed coral or something to raise the pH of the bark? And if you do, at what ratio? These plants have been sorely neglected for the past few years so I'd really like to help them do better. Thanks in advance!

[Ray]

All plants need calcium. They do not necessarily need the pH to be raised.

Before you go throwing stuff at the plants, do you know how much calcium (and magnesium) are already in your water supply?

[varda.elentari]

Thanks for responding Ray! According to the most recent water report I can find (2019), my tap water averages 35.6 mg/L calcium and 9.3 mg/L magnesium. I was thinking of using water from my aquariums to water though so perhaps a little less if I factor in nutrient uptake by the plants in my tank?

---------- Post added at 06:34 PM ---------- Previous post was at 06:16 PM ----------

And I meant raise the pH because from what I've read fir bark is too acidic so I've seen some sources recommend adding dolomite lime. It's hard to find where I am though (except in huge bags that I'd have no use for) so I wondered how many growers go without.

[estación seca]

First, your water has enough calcium and magnesium for your plants. If you adjust the pH to 5.0-6.5 your plants will get plenty of both from your water. Pour water through your plants in bark, and collect what flows out. Measure the pH of that. You can get test paper or liquid test kits at shops selling aquarium or swimming pool supplies. Do not rely on a cheap pH meter bought onlne; they are rarely accurate. Use a product from a hydroponics store nearby to adjust pH up or down. I use vinegar, but people growing in clay pots say it makes the pots deteriorate very rapidly. It also promotes algae on pots, which some people don't like.

Next, and this doesn't apply to you, since your water is fine as it is - calcium and magnesium are eluted in miniscule quantities from chunks of rock and shell. The more acid the watering solution, the more is eluted, but it's likely not enough for any plant. There are many recommendations to add egg shells and dolomite to this and that potting mix, but this is a nearly completely ineffective way to supplement with calcium. Plants often do well with egg shells in the medium because they contain some protein, which feeds soil microorganisms, which help the plants. But if you want to give more calcium to your plants, it must be in the water, and the water must be at a reasonable pH for plants to absorb it.

[varda.elentari]

Thanks so much for such a detailed explanation! That was incredibly helpful.

[Ray]

A little “fine tuning” on the pH factor:

Unfortunately, you can’t just test the drainage when watering, it needs to be collected a little differently to get a reasonably accurate measure.

• Water the daylights out of your plant with the solution of choice, being sure to completely drench the medium.
• Wait 30 minutes for the pot to completely drain and for the medium, plant, and microbes to come to a chemical equilibrium.
• Trickle about 50 ml of pure water (distilled or RO) over the surface of the medium and collect the drainage.

Thats what you test to determine the in-pot pH.

I usually shoot for 5.5-6.5, but anything +/- a full unit is acceptable. Adjusting the pH of the solutions you apply has remarkably little impact on that.

[varda.elentari]

Thanks for the info Ray! I'll have to order a pH test to measure (aquarium tests are usually in the range of 6.0 and above) but if it happens that my bark is less than 4.5, would you recommend adjusting in any way?

[Ray]

Originally Posted by varda.elentari

Thanks for the info Ray! I'll have to order a pH test to measure (aquarium tests are usually in the range of 6.0 and above) but if it happens that my bark is less than 4.5, would you recommend adjusting in any way?

First, I doubt it will be. Second, 4.5 is still acceptable.

I have measured the solution in S/H pot reservoirs - flushing and filling them with fresh solution at a pH of 6 and waiting a few hours has shown me pH levels as low as 3.5, but if fluctuates with time of day and plant activity.

[varda.elentari]

Thanks Ray! That's certainly reassuring.