Great success with poting mix experiment!

[treeman]

This spring I experimented with a potting mix idea which was rolling around in my head. I wanted a reliable long lasting mix for azaleas mainly but also tried it with gardenia and dwarf kumquat. It obviously had to be acidic. Kanuma is out of the question.
I used washed and screened scoria and peat moss. The scoria typically has a pH of about 8 (way to high) and a very low CHC and the peat a low pH of about 4 and a very high CHC. I assumed that mixing the 2 would bring the acidity to the right level (about 5-6) The proof would be in the growth response. I used scoria of between about 2 and 5mm with all traces of fines and dust thoroughly washed out. To this I added about 15% (?) peat moss straight from the bag. That's proper sphagnum peat NOT coconut. I added enough peat to slow down the drainage just a little (tested) and stopped adding after that. Into this mix I planted several azaleas and dwarf rhododendrons ( which can be difficult at the best of times ) after cleaning the roots. The growth of these has been outstanding. In fact, it's the best they have ever performed. They where top dressed with some low P osmocote and a little nutricote (higher P) with nothing else added. The colour of the leaves has never been better and the plants seem to have rooted strongly into this mix. There is no need to worry about a slumping or decomposing mix which always sets the plants back after a while. It remains to be seen how the second year in this mix goes but everything points to continuing good growth. In hindsight, it would probably be better to add some Iron and copper to the mix but even without this they seem to be doing very well. My small Rh kiusianum in particular looks like it has finally woken up from a thirty year potting mix nightmare and has grown more this year the previous 10! Another thing about the mix is that I have not yet seen wilting so it holds quite a bit of water.
The next step is to try other species and in particular I will try it out on some natives with a possible pH adjustment.

[TimS]

Very interesting indeed! Logically it makes sense they would balance each other, but it doesn’t always work like that.

Did you test the Ph with the two mixed together to get a definite result? Possibly you wrote that I just missed it! Have you tried anything with EC of fertiliser on them?

I gave up on Azalea early into Bonsai after poor results with them, but I might have to give it another go with this method.

[treeman]

[quote="treeman"] very low CHC and the peat a low pH of about 4 and a very high CHC.

That should be CEC of course

[treeman]

Have you tried anything with EC of fertiliser on them?

Not sure what you mean here but if you mean fert concentration, I will typically give half the normal amount to azaleas.
My EC meter packed up a while ago.

[alpineart]

Hi treman , mate I have been using 3-10mm Beveridge scoria and pine bark for well over a decade on all my potted material . Natives , Azalea's , Pines , Junipers , Crab apples , Maples and many others , all have performed well . I did add some Diatomite into the mix a few years ago to lighten it up for the big pots , but it wasn't the brightest of ideas.

Beveridge Soft Red Scoria retains around about the same volume of water as diatomite , however it will never deteriorate in my time . The diatomite is scattered all over the yard as a result of my watering method so my mix is improving with age back to the original recipe .
Every re-pot i wash the mix through 30% shade cloth into the grow beds { its easier when you have to wash 2.5 tonnes and add more 10mm minus aged bark

As for ph and all the rest of it , I fert with Rustica Plus which is very high in N P K which doesn't seem to effect the growth of my Natives , Azalea's or Gardenia's along with all the rest of the stock , considering I get a bit heavy handed which in some cases will burn the roots system and results in death which usually happens with a few days of overdosing

Cheers Alpineart

[treeman]

Hi Alpine
Yes I could use bark but what I wanted was a mix which was completely free from slumping or decomposition with it's structure basically unchanging. (and cheap) Instead of scoria I could use diatomite or pumice of course but the scoria is readily available and very cheap. The important component here though is the peat. Bark is ok but as it decomposes, I find azalea roots hate it and turn brown rather than staying clean and white and you need to remove every trace of it sooner or later. There's no doubt in my mind that they are happier in this mix than in bark mixes as evidenced by the improved growth and leaf colour. Of course it's more than just mix which is important but it's a good start. I don't think I would use this mix for old trees (?) where I want very fine ramification. For those I still believe a softer soil/akadama is best as the particles are compressed by root pressure and hence more spaces for fine roots are created. Azaleas do not have this type of root system as you probably know and should not be ''stressed'' by too much root density which always leads to a weak plant.
Years ago I talked to the Japanese owner of New England Bonsai in the US about azaleas (when I was really into them - not so much these days) and told him I used bark, the look on his face was not pretty as he said ''No good! rot!''

[longd_au]

Thanks Treeman. I have been looking for a mix to put my azalea in and this sounds like the perfect experiment.