Is pH adjustment really necessary for fertilizing in S/H?
 

Two questions about pH adjustment in fertilizing in S/H:

1. Is it really necessary? If I don't do it, what would happen?

2. How do most people do that? Using another product to bring the pH down and testing their solution? Or, do they just add a few drops of lemon juice or vinegar?


Thanks

Right from the start, considering the inert nature of LECA, I was fanatic about adjusting the pH of the fertilizer solution.

However, I have since learned that the plant and the microbes inhabiting the rhizosphere play a much bigger role in controlling the in-pot pH than I had realized.

I urge you to test it yourself:

• Water with plain water, then wait 30-60 minutes, then drain a tiny bit of water from the reservoir and test the pH.
• Repeat that using a fertilizer solution for which you have corrected the pH.
• Repeat the test using a fertilizer solution - unadjusted.

After my experience with that testing, I simply don't worry about it any more, but be aware I am using pure water; your results might differ if your water supply is hard or substantially alkaline.

the difference will be that leaves will not grow as big, will flower less and could even become so weak that they die.

I check my ph because it is one of the very few factors I am fully in control of, if like Ray says you find you are lucky enough not to need to adjust it then you don't need to worry about it but if your ph is far too high then over time the plant will grow slower and if it grows too slow it can't keep up with it's vegetative and flowering cycle, either it skips a flowering cycle or it just gives up.

It's easy to lose orchids through bad care so best give them what they need and it can still be challenging. Like Ray says you might find you don't need to adjust and the orchids will be fine as they are.

If mine needs adjusting I use ph down solution from my local hydroponic shop and I use it at a strength of 1 drop per liter to adjust by 1 ph, so to get it from a ph of 7 to 6 I add 1 drop. If I accidentally add 2 drops I need to start with a fresh batch as that will lower it too much so you don't need much of it. (working with a 10l bucket is easier as it needs 10 drops)

To put it into perspective on how important or not important it is in my opinion I have thought about it hypothetically :

If I were to have an orchid sitter look after my plants for a year and I had two choices for their care:

a) the right ph but no fertilizer for a year
b) the right fertilizer but the wrong ph for a year.

I would pick scenario a over scenario b for my orchids every time as in scenario a they will have full access to every nutrient they need but in sceanrio b although they will be getting fertilizer added they won't be able to absorb it well and will suffer more than with a reduced amount of fertilize in scenario a as water contains enugh nutrients to keep an orchid alive but if nutrients are locked out because of a wrong ph then the plant will suffer more.

Nutrients being “locked out” or the plant’s inability to take them up is the fallacy of the argument.

Unless the pH is extremely high or extremely low, the nutrient ions in solution stay in the intended form and do not precipitate, so are available to be absorbed by the plant.

It may be that this orchid-growing lore originated with a published study from decades ago, but ignores the fact that it was an experiment using a single fertilizer formula being used on a single sample of soil, where such “trapping” is a real and significant phenomenon.

The fact that it is pour-through results from a soil substrate really confounds its value to orchid growers, as soils can have significant cation exchange capacities (CEC), while most orchid media have orders-of-magnitude less, if at all.

The cation exchange capacity is a measure of how well soil components hold onto positively-charged ions – cations – and much of the CEC occurs at the edges of clay particles. The development of positive and negative charges on a clay particle is affected strongly by pH, so we can understand how, at extreme pH values, the charges may strongly bind the cations in fertilizer solutions, making them unavailable to the plants. In orchid media, which tend to have essentially no CEC, the nutrient cations tend to stay in solution and remain available.

Yes, pH can affect the plants’ uptake dynamics, but again, unless the pH is way out of bounds, the effect is minimal.

Over the last dry year I've collected less rain. I've run out several times, and been too lazy to go to the aquarium shop for multiple buckets of RO water. My tap water has pH of 8-8.5 and dissolved solids between 800 and 1,200 parts per million. I haven't noticed much difference with most larger orchids. I'm even seeing decent growth with larger Pleurothallis.

So I think lots of bad water is better than not enough perfect water.

I don't bother with it at all and my plants do NOT weaken and die, they grow and bloom quite normally.

I've never bothered testing pH regardless of using a traditional bark mix medium, sphag only, or semi-hydro. And over the years have used tap water with a 8 to 9 pH, down to straight from the R/O system.

Only thing I've ever really seen a difference in growth or bloom was when using tap water with high pH and really high TDS, then switching to R/O for more sensitive genus, e.g., Phrags. And that wasn't about fertilizer... way too high TDS.

Does it make a difference? Maybe to a botanist, a commercial grower with a lot of money to make or lose, or someone who's just really into biology/chemistry. To my hobbyist eye, not worth the effort.