Semi-Hydro and pH adjustment

[orchidsunlover]

Hello everyone,

My entire collection of orchids are in semi-hydroponics which are on heat mats and under LED lights. I find that my after pouring my 5.8 nutrient solution on my orchids in leca (I'm super meticulous about the pH), that the pH raises after an hour or so. The pH can fall low or high depending on the plant. Certain plants pH also falls faster or lower depending on the plant as well. If I have time on that particular day, I put the pH back in the range I want it at, which is at a pH of 5.8 using pH up or down.

My question is for days I am busy or on vacation, how can I prevent the pH from falling or going up from that range? Is pH adjustment inevitable due to orchid absorption of the nutrient in the semi-hydroponic solution?

Some suggestions on what I can use or do, or why this happens would be honestly great!

Thank you!

[estación seca]

The pH excursions you describe won't have much effect on your orchids. I wouldn't worry about it. I grow a lot in S/H and no longer measure pH.

[orchidsunlover]

Hi Estación seca,

Thank you for the quick reply! One question, since you no longer measure the pH, do you notice any nutrient deficiencies?

What I've learned is that orchids having a certain pH is crucial for nutrient uptake. So I take it this is not correct?

[Ray]

Let me jump in on this subject, as it's one of my "hot buttons" against misinformation.

Unless it is WAY out of whack, meaning extremely acidic or basic and leading to precipitation, the pH of a solution has essentially no bearing on the nutrients' ability to be absorbed. The old "Nutrient Availability" graph we've all seen is related to the pH of SOILS, not solutions.

Soils, courtesy of raw clay and microscopic organic particles, have charged sites that can react with aqueous ions. That property is known as the "cation exchange capacity", or CEC. At certain pH levels, those sites attract and hold certain charged ions; at other pH levels, they may release those and trap others. Nutrient ions that are so trapped, are not in solution, so are not available for the plant to take up. The clay media used in semi-hydroponics are fired and partially vitrified, so they act nothing like the raw clay particles in soils.

Orchid media have essentially no CEC, so that process does not apply, and as orchids do not get their nutrition from soils, if the nutrient are in solution, they are available.

[Dimples]

The pH creep is related to nutrient uptake by the plants, roots trade hydrogen ions for anions causing the pH to drop over time, though there are usually other factors at play. If you mix and use the solution right away you should try waiting 30min after you pH adjust, recheck the pH, and then go from there. The initial drop/increase isn’t necessarily the same as the final pH and that can take a little while to stabilize.

---------- Post added at 03:10 PM ---------- Previous post was at 03:09 PM ----------

But as ES said, the pH changes your seeing aren’t concerning.

[orchidsunlover]

Ray,

Thank you for the very detailed explanation on why pH doesn't matter as much as I thought it did! I really thought that having it at a pH of 5.8 was really going to help my orchids in semi-hydro grow a lot better! Now I don't have to be so meticulous about it as I was before. That is such a relief, haha.

Dimples, yes, I thought so too! That you for clarifying that aspect of my question! I've never tried waiting 30 minutes after pH adjustment, I'm going to have to try that out trick out! Thank you!

[Ray]

Orchids and pH › First Rays LLC