Say if I used the gritty mix without the pine bark, or used leca and rockwool and a growpot, and added Foliage Pro when I water, would I ever need to repot?
Yes, you sure would.
Roots continue to grow and colonize the mix until there is no more room. Plants growing long-term in containers require root-work to stay vital.
I agree that there will always be root work required on say a tree in a pot in order to maintain vitality. Something like an orchid on the other hand, not so much. So I guess the answer is, "it depends." The nice thing about getting rid of the organic faction in the mix is that you don't ever have to replace the medium. LECA is going to say LECA effectively forever. So once you have it on site, you don't have to carry more in and out periodically in order to deal with decomposition. This can be a big deal if you live in a 12 story walk up. I have also found that plants seem to be able to go longer between pottings when kept in an inorganic mix because at least they don't have to deal with the structure failing. Which of course means that I sometimes neglect my plants. lol
But I'm not sure if you are familiar with Rootmaker pots? They air prune the roots as they grow.
Here's their site: http://www.rootmaker.com
So it would prune the large roots and cause side roots to grow, but maybe what you are saying, Josh, is that the roots would at some point have to be thinned out because they'll fill the whole pot?
Nil13, I'm looking at LECA. Do you add any rockwool to help retain mositure or just use straight LECA? Was it expensive, for instance, to fill a large container? I have some 24 inch pots for instance.
Exactly, Lucy, the big old woody roots would need to be thinned so that younger more efficient roots can take over. Pruning the tips may work for a while, but eventually you've got to get in deeper.
Lucy, the videos on the rootmaker site are interesting. I learned a thing or two about root development. You would still need to transplant your plants regularly though, I think, because eventually roots do run out of space in any pot and giving them more space is the way to make them grow.
I would not use LECA for large pots. I would rather spend my money on plants. For large pots I use the Missouri Gravel Bed mix which is 2 pea gravel: 1 calcined clay (Turface). It's cheap and holds a lot more water than you would expect. The only problem is that since it's basically a bucket of rock, it's really heavy.