Potting practises, frequency of repotting

[Bjorn]

Mike, re the post above on calcium; I might have been unclear, but in my perception, the calcium is protecting the plants from sudden K poisoning not by being taken up by the plant, but by preventing K to accumulate in the colloids. That way, no effect would be seen on the plant growth. No deficiency symptoms in other words. If you have lime in your water (hard water) calcium supply should normally be sufficient anyhow.

 

[Bjorn]

Re the microbial situation. Could make sense that microbial action is accelerated by fertiliser. By the microbial activity, the colloid are produced and a high activity produces more, potentially harmful colloids. If they adsorb K of course. I have many pots recently that have entirely broken Down substrate that has perfectly healthy roots, almost without substrate!

 

[Brabantia]

Thanks Rick for your fast response and thank you also for the other participants at this very interesting discussion.
Here are some data I taked this morning on some of my plants.

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The plants are cultivated in a substrate made with70% bark/30% CHC at which I added 10% of small expanded clay balls. No dolomitic material added. As fertilyser I use a 4/1/1 NPK (not N/P2O5/K2O). The ratio NNO3-/NNH4+ is 85%/15%. I fertilise at 40 ppm N one time per week. At this Nitrogen concentration the one in Ca++ and Mg ++ is 30 ppm and 10 ppm respectively. Water used: rain water always.
Measured EC of the fertilyser solution ~ 350 µS. pH adjusted to 6 with KOH 1M.
Here are my conclusions after two years of culture using these conditions.
Using low or medium level of fertilisation with a fertilyser having a high proportion of Nitrogen in the nitrate form cannot regulate tightly the substrate acidification.
Because the high humidity, the presence of nitrate (an oxidizing agent) and the bacteries developpement, all these factors (and many more other for sure) leads to a situation where the substrate becomes acid and sometimes very acid.
This situation can be attained in the short or medium terms. (6 months to one year)
I have no data about the ideal pH for nitrates assimilation but in culture In-Vitro it is common to use a pH between 5.7 and 6.
My understanding of the reasons for which it is necessary as often to repot are :
The acidification of the substrate below 5.5 do not allow the nitrogen assimilation (and maybe other minor elements) and stop the plant developpement .
The acidification create an environment favourable for the roots rot.
In my opinion (IMHO) this is the raison why Rick has so good results with so low nitrogen distribution and using a substrate made mainly with dolomitic stones mixed with some mousse ... the pH of its substrate is stabilized and the Nitrogen assimilation is thus optimized.
Maybe in the future we shall come back on the necessity of granular dolomite addition in paphiopedilums substrate. Not as a Calcium Magnesium source as it was recommended in former days but because its pH stabilization properties.
Your comments will be highly appreciated.

 

[Brabantia]

Here is what I noticed from the points of view health and flowering of plants.
More flowering ... due to the decrease in fertilisation (lower N and K concentrations) but more regularly (one time per week) and a better control of the potting humidity.
But ... the growth rates is very slow, many plants lose their leaves (the older leaves ... translocation) and the new leaves never reached the size of the leaves of the older shoots, the one when I bought the plant.
In conclusion the plants are regressing!

 

[Rick]

Bjorn,

there is possibly another thing to consider.
The effect of bacterial growth within the medium.
They grow and breakdown organic composts in proportion to the amount of nitrogen given to them.
Therefore giving less means they grow and breakdown the compost more slowly and it therefore last longer.
Is this correct or am I missing something?

David

This one I agree is the biggest factor with regard to mix "breakdown".

The CEC component causes mixes to become intolerant (toxic) faster, but shouldn't directly change the breakdown rate of the mix.

 

[Rick]

The acidification create an environment favourable for the roots rot.
In my opinion (IMHO) this is the raison why Rick has so good results with so low nitrogen distribution and using a substrate made mainly with dolomitic stones mixed with some mousse ... the pH of its substrate is stabilized and the Nitrogen assimilation is thus optimized.
Maybe in the future we shall come back on the necessity of granular dolomite addition in paphiopedilums substrate. Not as a Calcium Magnesium source as it was recommended in former days but because its pH stabilization properties.
Your comments will be highly appreciated.

I would disagree that the stone in my baskets is the cause of pH stabilization. The pieces are too hard and large for significant pH control.
If I used a more friable/granular product then I would get pH stabilization, but in my case I just get drainage.

However I agree that reduced nitrate input (and increased aeration) supports much less microbiology that runs the pH down. Wang presented work that indicated as such by comparing pH of fed versus unfed moss substrates. The unfed moss pH stabilized at > 5.0 while the fed substrate dropped continuously during the trial (I can't recall how far below 4.0 s.u.). Adding a plant made it even worse. The carbohydrate exudates of a heavily feed plant seemed to add fuel to the acid production of the microflora.

 

[Rick]

Re the microbial situation. Could make sense that microbial action is accelerated by fertiliser. By the microbial activity, the colloid are produced and a high activity produces more, potentially harmful colloids. If they adsorb K of course. I have many pots recently that have entirely broken Down substrate that has perfectly healthy roots, almost without substrate!

Very little K is taken up by microbes. Which is why Xavier showed increase in K with the different mixes.

These bacteria are the same as for the wastewater species we use for sewer plants. We can't get any appreciable uptake of K, even though we would like to reduce it on influent waste streams.

 

[naoki]

Lots of interesting ideas, Bjorn! A lot of things you mentioned is something I haven't thought about, but it does make sense (even though I don't know about chemistry as much as you do).

One thing I'm not sure about is what you said about the pour-through. Is it true that once cations are attached to a negative site, it doesn't get released, so pour-through can't detect it? I have thought that the bind is more dynamic than static. I looked at a paper measuring the CEC of pine bark (Thomas and Perry. 1980. Ammonium nitrogen accumulation and leaching from an all pine bark medium. HortSicence 15: 824-825). And you are right, there are some cations which can't be removed by leaching by water, but the amount seems to be pretty small. They soaked bark in DI water for 72 hours. Then they put barks into a column, and started to drip 200 ppm N ammonium sulfate, and measured ppmN of drips from the bottom of the column. Then they leached with water after the output ppmN reached to the equilibrium (around 192 ppmN). Majority of N get leached out, but 1.94% of the total applied N remained in the bark. With sphags, maybe these unreachable cations could be high and cause the problems you are talking about.

Now, my question is how much the sudden release of cations contributes to raised EC (or osmotic pressure is what roots really care). If it is really a problem, can't we detect the increase in the EC of pour through after pouring the fertilizer (i.e compare the EC of fertilizer and EC of pour-through with the fertilizer)?

Brabantia, so pH and EC seems to be pretty stable. As Rick mentioned about the Sphag moss acidification study (Yen et al. 2011, HortScience 46(7):1022-1026), the authors concluded that the main cause of pH decline was due to the root excretion (there are some contribution from types of substrate and whether the fertilizers are applied, but the authors considered that these other factors to be minor). Then, they conclude that low pH is not an issue for the production of Phalaenopsis (Paphs would be possibly different) since the growth of Phals were normal (even around pH of 3-4).

 

[Rick]

Brabantia, so pH and EC seems to be pretty stable. As Rick mentioned about the Sphag moss acidification study (Yen et al. 2011, HortScience 46(7):1022-1026), the authors concluded that the main cause of pH decline was due to the root excretion (there are some contribution from types of substrate and whether the fertilizers are applied, but the authors considered that these other factors to be minor).

That's a different conclusion from what I got (especially from fig 1).

-Moss with no plant or fert stayed at average of 5.0 su (after initial drop to ~ 4.0).
-Moss with plant but 0 fert went from 5.0 to leveling off average of between 3.5 to 4.0
-Moss with no plant but fert added immediately went to pH 3.8 and eventually crept down to ~ 3.5 (almost no change just constantly low).
-Moss +plant +feed started at the same spot as the fed only pot (about 3.8) and eventually declined to about ~3.0.

So over 1 pH s.u drop just adding N in the first place, but plants contributed another 1s.u drop to the fed and unfed condition.

I believe N rate was 200ppm in these trials and the trial length was only 30 weeks. Peak lows by 12-15 weeks after which seemed either leveling off or recovery.

 

[Rick]

I think the conductivity track on these trials was interesting too.

If we equate EC with "food". Then it appeared that only a tiny amount of "food" was "consumed" by the plant.

The EC of unfed moss, or moss w/unfed plant was 0.0dS/m

The EC of the fed conditions was 1.25dS initially and climbed to almost 2dS for the no plant pot, but stayed level at 1.25dS for the fed + plant condition.

The difference (0.75dS) at the end of 30 weeks would be combined plant and microflora uptake. This difference suggests that only 38% of what went into the pot was taken up by anything (plant or microflora).

 

[Rick]

The plants are cultivated in a substrate made with70% bark/30% CHC at which I added 10% of small expanded clay balls. No dolomitic material added. As fertilyser I use a 4/1/1 NPK (not N/P2O5/K2O). The ratio NNO3-/NNH4+ is 85%/15%. I fertilise at 40 ppm N one time per week. At this Nitrogen concentration the one in Ca++ and Mg ++ is 30 ppm and 10 ppm respectively. Water used: rain water always.
Measured EC of the fertilyser solution ~ 350 µS. pH adjusted to 6 with KOH 1M.

Brabantia. Where does your Ca and Mg come from? Also ammonia is antagonistic with K, Ca, and Mg. And bacterial nitrification of ammonia consumes alkalinity like crazy. With 6 ppm of your 40ppm N total in ammonia, that's a ton of bug food, and a big chunk of alkalinity reduction.

I think your K input is still to high. At 4-1-1 with N at 40, but adding KOH to adjust for pH that's still at least 10 ppm K ( and 10 times the K concentration in PK root water in situ). With K lite at 40 ppm K is down to ~3 ppm. Still 3 x higher than what PK see in the wild, but getting into the realm of natural surface waters.

I'm pretty convinced that even 40ppm (assuming you are saturating the pots at each feeding) is still way to much. Why don't you try 10ppmN for a while?

I'm pretty sure Mou Zong-min paper on Nitrogen requirements for P armeniacum was linked a ways back by Naoki, but doing the math.

They fed 50 ml of up too 420mg/L N solution into already saturated 785 ml pots. ONCE A MONTH.

Simple math. Each pot received 0.05 L of solution (21 mg) spread out into a 785 ml mass of wet moss (26 mg/L).

Not accounting for microflora competition, that averages 0.89 mg/pot per day (or 6.2 ppm per weekly dose). (Now we are back to insitu PK root water concentrations)

Also that was the high concentration. "Optimal" concentration varied from 105 to 420 ppm N solution strength depending on the parameter( vegetative growth versus seed germination rates for examples). The plants did fine from 0 to 420 ppm N solution strength. Just some parameters better than others.

So when figuring dose need to include more than just ratios and solution strength into the equation. It doesn't take much to make the orchids happy.

 

[Bjorn]

That's a different conclusion from what I got (especially from fig 1).

-Moss with no plant or fert stayed at average of 5.0 su (after initial drop to ~ 4.0).
-Moss with plant but 0 fert went from 5.0 to leveling off average of between 3.5 to 4.0
-Moss with no plant but fert added immediately went to pH 3.8 and eventually crept down to ~ 3.5 (almost no change just constantly low).
-Moss +plant +feed started at the same spot as the fed only pot (about 3.8) and eventually declined to about ~3.0.

So over 1 pH s.u drop just adding N in the first place, but plants contributed another 1s.u drop to the fed and unfed condition.

I believe N rate was 200ppm in these trials and the trial length was only 30 weeks. Peak lows by 12-15 weeks after which seemed either leveling off or recovery.

This is exactly what I try to explain in that long thead above. The moss has hydrogenated sites. When you add fertiliser, the cations that adsorb on the moss releases H+ which is acid. Additionally, there is some acidification by the roots excreting H+ to get to the adsorbed cations.
Just one thing we should remember; pH is the negative logarith of the H+ concentration, so a pH of 4 signifies 10 times more H+ than does a pH of 5. You all know that, but its good to remember.

 

[Bjorn]

Very little K is taken up by microbes. Which is why Xavier showed increase in K with the different mixes.

These bacteria are the same as for the wastewater species we use for sewer plants. We can't get any appreciable uptake of K, even though we would like to reduce it on influent waste streams.

You are too hooked up in micro-organisms, Rick. I am talking about colloids, micro and nano-sized particles that is the building stone of soil and the result of microbial break-down of e.g. bark.

These colloids that are typical for a broken-down mix has a significant CEC, much more than bark etc. Since calcium bonds much stronger to these colloids than potassium, sufficient calcium in the fertiliser can retard or block potassium adsorption. If potassium accumulates, a brief lowering of pH, eg by fertilising, can release large amounts that may not be very good for your roots.

The microbes have a part in this picture as well, but they are just consuming nutrients and producing colloids and what else they produce.

It is perfectly possible to grow paphiopedilums in pots with totally broken down compost. I have seen several examples of pots being filled with roots only and just a bit of remains of the original compost. Without root-rot.

 

[gonewild]

It is perfectly possible to grow paphiopedilums in pots with totally broken down compost. I have seen several examples of pots being filled with roots only and just a bit of remains of the original compost. Without root-rot.

And for each one of the examples you saw 1000 other plants did not survive the same declining conditions.

If a plant is able to grow a mass of roots before the media declines then it does fine. Why? Because the roots of orchids do not require solid media. They need humid space between solid objects like a crack in a rock, space between stones or wood, space between moss foliage or 2/3 of the root exposed to air while the other 1/3 is sucking onto tree bark.

What do you think the survival rate would be for Paph seedlings potted up into pots filled with totally broken down media?

 

[Bjorn]

And for each one of the examples you saw 1000 other plants did not survive the same declining conditions.

If a plant is able to grow a mass of roots before the media declines then it does fine. Why? Because the roots of orchids do not require solid media. They need humid space between solid objects like a crack in a rock, space between stones or wood, space between moss foliage or 2/3 of the root exposed to air while the other 1/3 is sucking onto tree bark.

What do you think the survival rate would be for Paph seedlings potted up into pots filled with totally broken down media?

And since some survive, there must be a reason for the death of the 1000. Why do those 1000 plants die? how can we improve the survival rate? I believe much can be done by a combined increase in Ca/Mg with a reduction in potassium. Actually much what Rick is doing, but from a slightly different angle.
Growing in an entirely broken down media? no idea, perhaps if you could make it really well aerated and free of pathogens?? After all, we do not want to kill those seedlings. I think I have to try with some leaf-mulch one day, has to be pristine from the forest floor, not a chemically infused mush from any pot. Wrong fertiliser routines destroy the mush, making it poisonous. That is what I try to explain.
Anecdotal: I used to have a tray in which I grew P. micranthum with great success for 10-12years without repotting. Sorry to say but the bark based mix got quite mushy after all those years. The plants did not suffer until I started fertilising and after two years the whole thing collapsed. Why? was it because the mix could take 10-12 years only? or was it because I started feeding (at 3-400ppm)

 

[gonewild]

And since some survive, there must be a reason for the death of the 1000. Why do those 1000 plants die?

Good question. Perhaps it's part of genetics that leads to evolutionary change. Maybe the one survivor just grew fast enough to be past the need for the media by the time the media became bad. Maybe the 1000 died because of the same conditions that caused the media to become bad??????

how can we improve the survival rate?

That was the focus on reducing the K levels. Now that some positive results have been observed different ideas are coming up, perhaps it's not the K but another element? The way we can improve the survival rate is to keep an open mind and try new ideas. Don't just fall back and rely on published science assuming the researchers knew what they were doing.

I believe much can be done by a combined increase in Ca/Mg with a reduction in potassium. Actually much what Rick is doing, but from a slightly different angle.

Very much worth continuing with your direction.

Growing in an entirely broken down media? no idea, perhaps if you could make it really well aerated and free of pathogens??

Then it would no longer be a broken down media.

After all, we do not want to kill those seedlings.

NO we don't! That's why we want to look at new ideas that have not been tried. Because so far most media breaks down quickly and that results in the decline in plant health and survival.

I think I have to try with some leaf-mulch one day, has to be pristine from the forest floor, not a chemically infused mush from any pot.

Can I suggest that you not waste your time trying methods and ideas that have already been tried? Leaf mulch was abandoned many maney years ago as a viable media for container culture.

Wrong fertiliser routines destroy the mush, making it poisonous. That is what I try to explain.

Agreed. That is why Rick looked at K levels. Now you suggest perhaps Ca/Mg may play a more major role. So focus on the elements not the leaf litter. What in leaf litter might make a difference? What around the roots makes a difference?
Looking at what is around the roots is why I started saying most of the nutrients for orchids are coming from organisms and not dissolved salts in runoff water. How and where do the orchids get their Ca/Mg? Figure it out! I've tested water flowing over moss covered limestone here in Peru and get 0.0 ec reading so the calcium from limestone is not in the water as a salt.

Anecdotal: I used to have a tray in which I grew P. micranthum with great success for 10-12years without repotting. Sorry to say but the bark based mix got quite mushy after all those years. The plants did not suffer until I started fertilising and after two years the whole thing collapsed. Why? was it because the mix could take 10-12 years only? or was it because I started feeding (at 3-400ppm)

My guess is your media may have lasted forever had you not killed the organisms that had established in your micro environment when you added salts. :sob:

 

[troy]

I repot all my plants in clear airy pots when they outgrow the pots they are in but after a few days I look they are bone dry, I don't soak the new media, should I flush The pot, I use straight ro water another question ro water is unstable how could I stabilize it?

 

[troy]

Gonewild, I read yur message got me thinking awhile back I started using only organics and it's worked very well for me although I do beleive there are still salts in it, what do you fertilize with? And what potting media do you use?

 

[gonewild]

Gonewild, I read yur message got me thinking awhile back I started using only organics and it's worked very well for me although I do beleive there are still salts in it, what do you fertilize with? And what potting media do you use?

Yes organics have dissolved salts much like commercial chemical fertilizers.

I use chemical fertilizers.
Historically I used maximum doses of nutrients every time I watered to grow plants as big and fast as possible. It works very well. But over the years of growing I observed various disease and plant health problems with plants that were grown "forced" for extended periods of time. I never associated the growth problems with excess nutrients until Rick proposed the Potassium toxicity concept and suggested that he noticed less rot with less potassium. He had enough observational success that I tried it myself and also noticed an improvement in the "disease" issue.
It became obvious to me that the disease was not a disease at all but instead it is a result of the plant reacting to an overdose of nutrients.
Does not matter if the nutrients come from chemical or organic fertilizer once the nutrients are dissolved they are basically the same salts in the water.

Now I am experimenting with various combinations of nutrients and so far I am in agreement that lowering the potassium level in fertilizer is a huge advance in plant/nutrient health quality.

Without doubt using low levels of potassium is better than high levels, that I have proved to myself.

I have grown in just about every type of media and can say that media type is not the main issue. You can grow an orchid in or on almost any material as long as you adjust the water and nutrients to adapt to the media. That's not to say that all medias work well! In my opinion the best media is a media that is alive and not dead, but that is pretty difficult to manage in a small space.
Right now my main ingredient in my substrate is Brazilnut shells and that may or may not have been a good idea.
But it is giving me insight and answers about potassium toxicity.

I don't like growing in bark medias because they breakdown too quickly. So far the best mixture that I have found was a mix of Leca, CHC, charcoal and pumice. It holds moisture but is very open and has air space. In an open airy media it is easy to repot more often as the media decomposes.

 

[Brabantia]

Brabantia. Where does your Ca and Mg come from?

From Calcium nitrate (YARA) and Magnesium nitrate (PA).