Can i use the 5-1-1 mix but add some of the components of the gritty mix to make the soil last longer? Unquestionably, you can do whatever you like, but I can offer some input insofar as what to expect. Either medium will last at least as long as the point in time when the roots become so congested a full repot would be required to ensure your plant has the best opportunity to realize as much of its genetic potential as possible. If we assume you're able to maintain the plant at a high level of vitality, roots will likely congested to the point where they would benefit from a repot in spring at the beginning of the 3rd growth cycle, and definitely by spring of the 4th growth cycle (probably stretching it but not endangering the plant's viability).

As the 5:1:1 mix breaks down much more slowly than finer materials. By the time it has broken down to the point where you should be concerned about the soil's structure, the plant's roots are becoming a part of the soil's structure, so the real issue is the volume of soil (carbon) will be diminished by the soil gassing off (as CO2). The diminishing volume of soil will be unable to hold an adequate supply of resources, that, couple with the fact heavy (thick) roots with very few branching fine roots will have filled the pot at the expense of those fine roots that do all the plant's heavy lifting. The primary reason for repotting is to remove heavy roots to free up space for fine roots to grow.

Because the gritty mix is structurally more porous, it offers roots an extremely welcoming environment for growth, which typically shortens the interval between appropriate (timing of) repots.

Will the gritty components just separate out and not add any benefits? Are there reasons not to combine these two mixes such as pH or nutrient conflicts? The gritty mix will not likely stratify in the pot unless you aggressively flood the soil before the roots have colonized the entire soil column. It's primary benefit lies in the fact that it is a healthier environment for roots until root congestion fills the greater air space it offers; then, it becomes just another medium until you repot.

Al

Thanks for info, Al.

I confess I have sometimes let 5:1:1 and Gritty mix have a baby. Most often is changing pots and re-using soil mixtures that aren’t broken down much, so the bark fines, which are often Reptibark, so not cheap, are still good , and I’m not always running properly labeled bins of used soils ( “ used 5:1:1”, “ used unknown potting soil”, etc). Or, a pot has just been drying out too much as pure gritty.

Just because you mixed the 5:1:1 and gritty mix together doesn't mean you did anything 'wrong' or shot yourself in the foot. What it all boils down to is this: If you want to mix the gritty mix together with 5:1:1 you will introduce a perched water table, which the gritty mix is designed to eliminate entirely or almost entirely. You will have a medium roughly equivalent to the 5:1:1 mix in terms of usability and productivity, perhaps slightly but not conspicuously better than the 5:1:1, but not as good as the gritty mix in terms of drainage and air porosity. Still, you'll have a much better medium than you'd be likely find in bags or bales of media based on a high % of fine materials (peat, coir, compost, composted forest products, .....) .

I'm not here to talk anyone into anything; rather, I try to provide reliable and straight forward information that can help others make an informed decision. I look at that as an extension of my own growing experience, and getting all wound up about what someone chooses to do would diminish my enjoyment. If someone disagrees with something I put forward and I think what was said has the potential to diminish readers growing experience (because it's inaccurate or biased) I'll support my position, not because I care all that much about what they think. It's not because I want someone to 'do as I say', rather, it's because I wouldn't want info offered in error to lead you down a path that limits your enjoyment or potential for success/ best results.

When we lack the information to make the best decisions, we usually don't (make the best decisions); however, when we are well informed we still might make a compromise due to how our priorities are ordered, but at least we understand we're making a compromise and how to fix it next time if that doesn't work out. That's how I look at things. YMMV

Hope you're having a good weekend. I'm repotting like a maniac. It's supposed to be quite warm for the next 12 days, once we get beyond tonight's freezing temps. Starting tomo, I wont need to bring my temperate plants, now on carts, in and out of cover overnight. Below is about 1/3 of the temperate plants.

Al