@gardengal48 (PNW Z8/9) I believe you also mentioned that your container Rhododendron do not do well after a few years. I would like to solve the mystery of why that happens. I was hoping the soil testing might give some clues.

But if the problem is the bark in the container soil decomposes and ties up nitrogen, I guess the soil test is not going to show that anyway. That's frustrating.

Rhododendrons and azaleas are not ideal container subjects but they should do fine if planted in a relatively acidic media as well as a proper addressing of watering needs. I've grown rhodies in containers for 10 years or more!

Bark fines are pretty slow to decompose in a container setting and if one is fertilizing as often as necessary, then any nitrogen tie up or unavailability is moot.

@gardengal48 (PNW Z8/9) If you want to add just nitrogen, what are your favorite sources?

It would be very rare that I would ever want to concentrate on just supplying nitrogen. With the frequency of watering required for most containerized plants, ALL the nutrients (that are not tightly bound) will leach out and will need to be replaced. And my first choice for any containers is Dyna Gro's 9-3-6 at the maintenance rate every 7-10 days. If I wanted to supplement that with any additional N (can't think of why I would), I'd probably opt for alfalfa tea.

seems like the easy answer is to repot in fresh media every other year ....

its the old cost benefit ratio ... what will cost more.. a pot of new media.. or a dozen amendments to old media.. plus the cost do the soil test..

and consider that you would have to test every pot.. for lack of consistency across all pots...

ken

btw.. this is avoided in the grow industry.. when they have to up pot every other year ar two ... ken

Pretty solid reasoning, ken :-)) Although the need for routine fertilization does not change.

@gardengal48 (PNW Z8/9) On my other thread that included the soil test, the University of Massachusetts lab recommends fertilizing the raised bed soil with nitrogen and no P and no K. I guess that is because the soil is already too rich in P and K. This is a raised bed not a container. I tried to point you to that thread previously but not sure you received any notification.

https://www.houzz.com/discussions/6434046/correcting-iron-deficiency-for-camellia

Well now, I am well and truly confused! Are you wanting to know the validity of a soil nutrient test done on a soil-less potting media or are you asking how to address the chlorosis on a camellia being grown in a raised bed? Sorry, but if there is a connection between the two, I am not seeing it.

I've given my opinion on the need for a soil test on a container soil - something like the 5-1-1 mix - and I just can't see a case being made for it.

The camellia is an entirely separate issue. As I noted previously, N is seldom evaluated by most professional soil labs as it does not generate an accurate picture, given the constant fluctuation in nitrogen levels. Several things strike me about the UMass report. The first is that the pH level is higher than preferred - I'd shoot for 6.0. Second, the Fe level is only slightly less than optimum but its availability is being hampered by the too high pH. An insufficiently acidic soil will bind iron and make it unavailable to plants. Finally, I did not interpret the test to recommend fertilizing with just N, only that if any fertilizing were to be done, nitrogen would be the only nutrient needing to be supplemented......all others are present in adequate or more than adequate levels.

Chelated iron will immediately address the current chlorosis. And once you have lowered the pH appropriately, you should not need to reapply. And if the camellia is otherwise growing and looking as expected, then I doubt any fertilization will be necessary.

I have two threads. In this thread, I am simply asking if it makes sense to test container soil.

In the thread I linked, I have a test result for a raised bed (not a container) that has an iron deficiency. Sorry that I cross linked threads and introduced some confusion.

I did try to add sulfur to the soil to adjust pH. Something strange happened there, because now the soil near the surface in places is highly acidic (<4 pH) so the sulfur did not dilute itself and spread out uniformly. The lower pH did not resolve chlorosis. I am afraid to add more sulfur.

The Camellia does not look healthy. It lost leaves on its inner stems and most leaf growth is at the tips. The situation looks stable, but the plant is not happy.

For now, I will treat with chelated iron. If that works to resolve chlorosis, I guess I could try Espoma Iron Tone and attempt to add organic iron as well as further treat acidity?

@gardengal48 (PNW Z8/9) I posted photos of the Camellia in that thread. I would be thrilled if you had a look:

https://www.houzz.com/discussions/6434046/correcting-iron-deficiency-for-camellia

' I did try to add sulfur to the soil to adjust pH. Something strange happened there, because now the soil near the surface in places is highly acidic (<4 pH) '

If the elemental Sulphur was merely broadcast on top of the soil, it would take several waterings for it to percolate down into the soil. You never said how it was applied but that thought popped into my mind when you said it was the top layer that was so acidic.

@BillMN-z-2-3-4 I did mix in the sulfur with the soil, but i think I did this minimally. In any case, it looks like the sulfur finally did disperse, and now six and eight-inch core samples are at pH 5.8, about right for Camellia.