Potting practises, frequency of repotting

Potting is necessary, but how do you guys practice it? According to "best practises" of paph growing, they should be repotted every two years or so. I never did that and most of my plants stay much longer in their pots. Traditionally I repotted when the plants started to sulk...
Recently, after starting fertilising at much lower levels I have noticed that root growth is better and that seemingly repotting is less necessary. Nowadays repotting is done at longer intervals and usually because the plant has outgrown its pot size.
Now, I wonder, what are the practises and experiences elsewhere?

about every two years. I find the mix goes off and the vigour slows. Also, I aim to have the plant 'outgrow' its pot in two years.

In order to answer to your question definitely we should know (or remind of us) what you use as potting and which fertiliser you use, how much and with which frequency. If you often made potting flushing or not. In effect the stability of the potting mixture depends on these factors. Do not trust in the visual potting aspect.

Since going to baskets, I've eliminated a lot of repotting hassle.

I still have stuff in pots, and have been experimenting with some systems that I gave up on years ago (like CHC mixes for barbata types).

In most cases I don't have a full 2 years on these trials since I didn't cut N application rates significantly more than 2 years back. But I am seeing results similar to yours Bjorn.

agree there are many variables. i grow in fir bark mix and repot annually.

I don't know if you remember that work by Xavier comparing Orchiata to other materials: But the type of material used makes a big difference on how much different fert components accumulate in the potting mix.

Orchiata accumulated roughly 1/2 the K compared to moss and coconut coir.

I suspect that would hold true for other metals like copper/zinc/iron/manganese that are in some fert mixes like MSU or Klite, and in general these are toxic to plants at lower concentrations than potassium.

So if buildup of toxic materials is the driver for repotting, the rate would be 1/2 for materials like Orchiata relative to coconut coir.

Bjorn said:

Potting is necessary, but how do you guys practice it? According to "best practises" of paph growing, they should be repotted every two years or so. I never did that and most of my plants stay much longer in their pots. Traditionally I repotted when the plants started to sulk...
Recently, after starting fertilising at much lower levels I have noticed that root growth is better and that seemingly repotting is less necessary. Nowadays repotting is done at longer intervals and usually because the plant has outgrown its pot size.
Now, I wonder, what are the practises and experiences elsewhere?

Click to expand...

I've been on a 1 to 2 years repotting schedule for years. But there were some exceptions (some mature plantes in larger pots). I also waited about 10 years before trying to repot a Pinocchio. But it was too late Like many ST members, I now fertilise at lower levels and I noticed I could delay repotting.

Here's one of the more dramatic improvements via basket culture and starvation feeding.


This kolo was a pathetic virtually rootless 4" seedling when it went into the basket Dec 2010 (so almost 4 years ago). The wilhelm was also pretty sparse on roots going into the basket. It's coming back nicely too.

They were in this first group:
http://www.slippertalk.com/forum/showthread.php?t=18566&highlight=mark+date

You can see the original 4" basket the kolo was started in, and I just slipped it into a 6" basket when the roots started coming out the sides. The roots are already coming out of the 6" basket too.

Good to hear what Bjorn is doing. When you repot after a couple years, are the media completely broken down? I think yours is similar to Birk's mix.

I have been doing yearly repot (bark based), but I started to think why do we need to do it. Accumulation of "stuff" (either salt or root excrete) and decay have been said to be the reason. The other possibility is the possible pathogenic micro-fauna.

- EC/TDS doesn't seem to increase too much with low fertilization scheme (I haven't tracked pH, and shift with pH could be a problem).
- Break down of media may increase the drying time, but if the drying time is not too excessive, we can just reduce the watering frequency. Breakdown can also provide some nutrients.
- Maybe, microbe supplement (cermi-compost tea, EM-1, Innocucor etc) may contribute to longer repotting intervals? They probably could increase the decay rate, but they may be reduce accumulation of "pathogenic" fauna if this ever happens. Also the root excrete could be reduced by beneficial fauna (pure speculation).

Here's one of those root rotted lowiis from the group on the left. After I took the pic I repotted them all in fresh CHC mix.

http://www.slippertalk.com/forum/showthread.php?t=34792&highlight=tired

Not bad root growth for 3 1/2 months.

I'm going to try and kill it again. This time setting it up SH - hydroponically in glass beads, and try to refresh the solution daily with the 5ppm N feed I throw around the GH every day.

@Rick about your Paphio Kolopakingii in basket.

Have you any data on pH and EC of your substrate measured by the pour through method using RO water or rain water?

Brabantia said:

@Rick about your Paphio Kolopakingii in basket.

Have you any data on pH and EC of your substrate measured by the pour through method using RO water or rain water?

Click to expand...

Given that the substrate in the basket is mostly coarse limestone gravel (with moss around the edges, and water only stays in it for a short time there is probably very little buildup of minerals. This is very close to a mounted condition. I suspect I would have to pour the RO through several times to get a measurable number on my home meter. The most holdup would be in the moss, but it is probably not homogeneous throughout the basket. There is very little moss on the bottom, and a fair amount of exposed roots not in contact with substrate.

If I get ambitious I'll try to set something up to test.

The EC of the daily fertigation water is 60 - 80 uS/cm and pH about 6 the last time I checked.

Rick said:

I'm going to try and kill it again. This time setting it up SH - hydroponically in glass beads, and try to refresh the solution daily with the 5ppm N feed I throw around the GH every day.

Click to expand...

If it dies blame in on Silica toxicity.

Rick said:

I'm going to try and kill it again. This time setting it up SH - hydroponically in glass beads, and try to refresh the solution daily with the 5ppm N feed I throw around the GH every day.

Click to expand...

You might have trouble with the base of the not getting enough moisture an there is no capillary action from the glass?

Rick said:

I don't know if you remember that work by Xavier comparing Orchiata to other materials: But the type of material used makes a big difference on how much different fert components accumulate in the potting mix.

Orchiata accumulated roughly 1/2 the K compared to moss and coconut coir.

I suspect that would hold true for other metals like copper/zinc/iron/manganese that are in some fert mixes like MSU or Klite, and in general these are toxic to plants at lower concentrations than potassium.

So if buildup of toxic materials is the driver for repotting, the rate would be 1/2 for materials like Orchiata relative to coconut coir.

Click to expand...

I agree that you need to understand the media you use. I think CHC should get VERY low fert levels where as my brachys in lava and diatomite get plenty and are thriving. (sat in shallow water and in theory should not need repotting until ( I hope) they are bursting out.
Orchiata falls somewhere in between the 2 extremes?

Stone said:

You might have trouble with the base of the not getting enough moisture an there is no capillary action from the glass?

Click to expand...

Will have to see, and play with the depth. Also when I refresh I'll pour through the pot, which will re wet the upper roots. There's some roots all the way to the bottom and they'll be constantly submersed.

Also its in the GH with high humidity. I have some lowii in very open baskets with some roots totally free of substrate and still growing fine.

I'm a tad more concerned about the constantly wet roots than the dry roots.

If this was a phrag I wouldn't think twice about this.

Naoki, Rick, and everyone else that bothers, look into this approach on why low amounts of fertilisers make potting mixes last longer.

I think it is fair to say that one common experience is that when fertilising at lower levels, the potting intervals may be increased. The explanation involves the CEC (cation exchange capacity) of the substrate, or perhaps we should call it CAC(cation absorbtion capacity). Why? let me explain:

Most colloids and many organic structures like sphagnum, bark and CHC has active sites with the ability to dissociate and produce negative charges on the surface, which subsequently get some cation adsorbed. This is the way many (most) plants gets their cations; by removing a cation from its absorbed site, replacing it with a hydrogen ion (H+). That way charges are kept neutral.

Many components of the potting mix, particularly sphagnum, have these sites predominantly in the hydrogen form, i.e. no other added cation than hydrogen.
Once these sites are subjected to a liquid containing cations, e.g. potassium or calcium, the potassium or calcium replace the hydrogen and the moss liberates a certain amount of H+. This is acid and that is one of the reasons why e.g. sphagnum has an acid reaction in water.

Ok, after a while with fertilisers, all the sites are occupied with cations - which ones are dependent on their ability (concentration) and the size and charge of the ion. Generally polyvalent ions have smaller ionic radius than monovalent, so Ca2+ would replace K+ if fed at the same amount. But traditionally the content of calcium was not as high as that of potassium, so generally most sites would be occupied with potassium. Over time, when the substrate breaks down, more colloids are produced with more active sites that can adsorb cations. Over time, the amount of adsorbed cations can be quite high, and remember, this is adsorbed and will not be liberated unless they are exchanged by eg. acid. So measuring the amount by "pour through" will not measure it unless you pour through an acid.

If for instance you fertilise on a weekly basis, since the fertiliser probably is more acid than your normal water, this fertiliser may release quite a lot of cations and you might have a situation that suddenly gets more or less poisonous for your roots due to a massive liberation of cations. This will be primarily potassium I suspect, since once polyvalent ions like calcium adsorb, they will have excess charges available and the posibility of neutralising two negative sites. This can be done by linking two colloids. A typical example of this kind of reaction is stabilisation of clay by lime. The effect of that action is that the cations both gets immobilised and also that the colloids transform to an earth-like structure (this is soil).

If we restrict the amount of monovalent ions relative to polyvalent, e.g increase the amount of calcium and magnesium (and the micros for that sake) relative to potassium (and probably ammonium, NH4+), then the sites will be occupied by e.g. calcium , the calcium replaces potassium being adsobed.
A nice explanation to this is given in the link below:
http://www.terragis.bees.unsw.edu.au/terraGIS_soil/sp_exchangeable_cations.html
If your fertiliser contain ammonium, NH4+, that ion will compete with the potassium getting adsorbed. The adsorption Properties are similar, but a little more ammonium than potassium gets adsorbed: http://www.ipipotash.org/udocs/Interaction_of_Potassium_and_Ammonium_ions_in_Soil.pdf

What is the effect of all this? Simply that if the levels of potassium is kept low relative to calcium, then less gets adsorbed and the likelyhood of later getting a massive liberation is reduced. Also since some potassium is needed you cannot remove it entirely, but if the fertiliser contain ammonium, then adsorbtion of potassium is further reduced.(its probably much more complex than this but this is my interpretation).

If you start with a potting mixt that has a low CEC i.e. stay away from sphagnum and CHC, then things may work fine for a long time. If the bark is treated with calcium (Orchiata) then even better, and if you use a fertiliser with proportionally more calcium/magnesium than potassium, it would help as well. And last, ammonium helps also.

Comments?

compost breakdown

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

I agree with most of your interpretation. However I am yet to be convinced that lack of Calcium is very often a much of a problem. I think there is too much emphasis put on it.

My view:
I have been growing plants of all kinds for many years. Cacti, orchids, trees, shrubs, citrus, ferns, cycads, bromeliads, blah blah. No exageration to say I cannot ever remember seeing a classic example of Calcium deficiency ever! The plants grew well with good roots, leaves and flowering. Plants grown in a general ground bark mix with a medium CEC. Some desert plants which grow on pure hard limestone with no humus in the habitat did just as well as any others without added lime.

If fact even these plants resent lime in the medium. Until recently I had never used fertilizers with calcium of any kind in them and always with high potassium as well. The only Ca they ever saw was coming from the tap water. And it seems that this was more than enough. The only consistant problem was with citrus species lacking Mg but they are very prone to this anyway.

I also read somewhere that much of the Ca in Calnitrate becomes unavailable to the plant by forming insoluble Calcium carbonate. I don't know whether this is true or not but if it is it would further convince me that we just do not need to add much Ca. I had not used it in the past. I do now because I am aiming for a 75/25 nitrate / ammonuim ratio because many trials recommend this.

I have posted before some Dutch hydroponic data for a range of crops which recommends Ca additions (to rockwool substrate) of around one half of potassium in all cases for optimum results. EC varies according to crop senstivity to salinity. Why do we feel that orchids are so different in their nutrient ratios? EG; Phrags grow in the same general habitat as Anthurium.
Anthuriums are grown to perfection hydroponically with the above kind of nutrient formulations.

Don't we need to look at the big picture? I am begining to think we should take more notice of the growth response of the plant rather than worrying too much about superficial and incomplete theories about Ca content of leaves and habitat data.

Sorry Bjorn, this may not have much to do with your initial subject
But generally I think at least we all agree that the higher the CEC of the mix, the less overall feeding is needed. Lower additions of cations is necessary and probably frequent repotting is desirable to bring everything back to square one?

monocotman said:

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

Click to expand...

That is correct as I understand it. But the plant also sees less N and sometimes not enough.