Hi, Zippelk!

When using these mixes, container size becomes much less of a consideration.
Indeed, your plants can be grown in very large containers without fear of rot.

Weight, however, does become a concern - with the Gritty Mix in particular.
Your options would be a smaller container; but then you'd have to water more and
conduct root-maintenance/re-potting more often (at least every year). You could
also opt for a lighter weight container - plastic instead of terracotta or ceramic -
but the weight-savings would be negligable in a large container of moist mix.
Lastly, you could substitute some fraction of the mix to achieve a lighter medium.
If you start fiddling with the ratios, you'll probably want expert advice from Al.
I would recommend Perlite as a substitute, but I can't offer exact measures.

Josh

I disagree with greenman. It's really hard to tell when to water in the gritty mix. Most of the problems I had with my plants earlier this year revolved around that. As a result, my grapefruit was defoliated entirely. I had it in a 12 inch pot, and when I pulled it out 2 weeks ago, the roots hadn't come ANYWHERE near filling the container. I downsized to a 10 inch container which is still plenty big enough. I was sticking trees that should be in a 2 inch container into a 6 inch, plants that should be in a 6 into a 10 inch and it was almost impossible to tell when to water due to the small root zone compared to uncolonized potting media, which was always wet.

How large a container should be, or CAN be, depends on the 3-way relationship between plant mass, container size, and soil type, assuming correct watering habits. We often concern ourselves with "over-potting" (using a container that is too large), but "over-potting" is a term that arises from a lack of a basic understanding about the 3-way relationship noted, which should logically determine appropriate container size(s).

It's often parroted that you should only move up one size in containers when "potting-up". The reasoning is the soil will remain wet too long and cause root rot issues, but it is the size/mass of the material and soil type/composition that determines both the upper & lower limits of appropriate container size - not consecutive volume progression.

Plants grown in slow soils need to be grown in containers with smaller soil volumes so that the plant can use water quickly, allowing air to return to the soil. This (smaller soil volumes) and the root constriction that accompanies it will cause plants to both extend branches and gain o/a mass much more slowly - a bane if rapid growth is the goal - a boon if growth restriction and a compact plant are what you have you sights set on.

Conversely, rampant growth can be had by growing in very large containers and in very fast soils where frequent watering and fertilizing is required - so it's not that trees rebel at being potted into very large containers per se, but rather, they rebel at being potted into very large containers with a soil that is too slow and water-retentive.

We know that there is an inverse relationship between soil particle size and the height of the PWT in containers. As particle size increases, the height of the PWT decreases, until at about a particle size of just under 1/8 inch, soils will no longer hold perched water. If there is no perched water, the soil is ALWAYS well aerated, even when the soil is at container capacity (saturated).

So, if you aim for a soil (like the gritty mix) composed primarily of particles >1/16", there is no upper limit to container size. The lower size limit will be determined by the soil volume's ability to furnish water enough to sustain the plant between irrigations. Bearing heavily on this ability is the ratio of fine roots to coarse roots. It takes a minimum amount of fine rootage to support the canopy under high water demand. If the container is full of large roots, there may not be room for a sufficient volume of the fine roots that do all the water/nutrient delivery work and the coarse roots, too. You can grow a very large plant in a very small container if the root have been well managed and the lion's share of the rootage is fine.

I think that Zecowsay's issue isn't actually with the soil; rather, with his unfamiliarity with it. A properly made gritty mix is extremely difficult to over-water because it should hold no (or very little) perched water. I've repotted thousands of trees into the gritty mix w/o issues, so my guess is that there was some liberty taken with the recipe so the soil didn't function as it was meant to, or enough attention wasn't paid to watering technique or some other critical cultural influence.

Al

Without going into too much detail of the pros/cons of the gritty mix, I'd say my favorite attribute of the mix is that over-watering is not a concern whatsoever in my bone dry, 100's temps.

In some respects, I do agree with Zeco in that it can be a bit difficult to tell when to water -- that happened for me when I (incorrectly) watered it like a typical mix.

In a typical (non-gritty) citrus mix, I strive let soil dry out as much as possible, just shy of leaves wilting (the frequency changes throughout the summer). However, when I've done this with the gritty mix, I've pushed the limit too far where the bark will dry and become hydrophobic and then it goes downhill from there. Don't get me wrong, this happens in typical peat mixes too. And I've confirmed there is still moisture in the gritty mix long after I can "feel" it wet (Per Al, this is ~30% moisture level) -- many trees survive OK even when I missed a couple waterings in a row and the mix feels dry. But somehow the bark (starts) drying out even though some moisture resides within the Turface and is still available to the roots.

But again, the benefit is the freedom to water on a schedule (uh oh, I said the nasty word). I can water every 2nd or 3rd day and it's fine. When it's crazy hot, I can even water every day -- for the sole purpose of cooling down the soil temps. I can't do that in normal bagged soil, b/c it will water log and start baking the soil anyway.

Other than washing out the nutrients too quickly, I've yet to see any ill effects of watering everyday in summer -- and I'm very experienced in early detection of over-watering in Citrus.

In fact, I've recently seen a set of citrus trees thriving in gritty mix, in NE corner of my yard, partially shaded (gets all AM, no PM sun), sitting directly on grass (soil is not directly in contact with the earth, tho). They get normal watering + sprinklers. I figured they would drown in two weeks, but they are now the FASTEST growing citrus in my collection. I am guessing b/c the gritty allows the excess water to drain and the humidity is very high in that shaded + sprinklered corner. Thus ambient temps are lower, moisture is high, and light is sufficient. Whereas the trees are struggling on my south side, even when shade cloth is applied, since ambient temps are 130+. Without cloth the leaves burn fast and fall off, although new growth is continually stimulated.

Oh and if weight is the topmost concern for your larger container, the real weight factor is the granite.

There are several in this forum who have replaced the granite with perlite as suggested above and the weight is reduced tremendously. However, as particle size is the concern with all three components of this mix, you'd need to sift the perlite to remove fine particles -- and you'll realize there will be lots of particles too small in a typical Miracle Grow Perlite bag. If possible, best to order a specific size or search the nurseries/big box stores for sized perlite (they'll be labeled Medium or Large).

If you're willing to do the work to find the ingredients and do proper sifting, I'd suggest gritty over 511. It's so much more flexible and lasts much longer and above all -- it looks way cool! You can impress your friends since you use a "special Bonsai soil" for your trees. But the gritty is certainly more work and more expensive upfront.