Hi, Personally I wouldn't do it. IMO, second year 511 is super for tomatoes all by itself. Mine grew better the 2nd year in the partially composted mix. I didn't add anything except 1/2 the amount of lime, but probably could have skipped it. You might freshen up last years mix with additional pine bark and a little perlite. Not sure why you want to add MG mix to it. What are your concerns. I'm using MG water soluble fertilizer also.

I'm not sure what is best for AV's? I cannot answer most of your questions. But I would not put lime in a soil you are watering with water that has a PH of nine! Holy Moly, that should kill everything! I would skip the lime, and yes use vinegar. I'm not really sure of the range of PH AV's like? But if you know go for the middle of the range. And no, mold is not a good thing. I know Al at one time had AV's and so the info you need might be in old posts. It would really be great for your plants if you could use rainwater.

Well, I'd be really impressed if you find a store that has all of those things! It took me a month to find just the 1:1:1 ingredients and of course they are at 3 different stores but well worth the effort. You'll find the gran i grit at a grain/feed store, the MVP Turface I found at an irrigation store (Ewing Irrigation - don't know if they have Houston stores), and I had to screen the Home Depot Sure Stay "Premium Pine Mulch" to get my fines. If you end up doing that, you can use the finest remaining particles in place of peat moss in the 5:1:1. Oh, and wall mart has perlite. Good luck to you on your quest, it is like a treasure hunt and so exciting when you actually find the stuff! Nik

@Nil13 made reference to the Whitcomb 311 mix, which is an earlier historical attempt to create a more coarse potting soil for container plants. I think it is extremely helpful to read a document written by Carl Whitcomb that explains how he came on this formula by accident. Essentially what happened is he accidentally left nine test pots under a bench and everyone forgot they were there. They had successfully nearly killed all of their test plants by watering in a normal potting soil mix and the unwatered plants started to do very well. What I have started to realize is that any plant can do well in many different soil mixes, if you are able to carefully control the watering. This explains why so many people on this forum claim gritty mix is not as good for their succulents as their (fill in some random horrible soil with lots of small particles) mix. Inevitably those people are growing their plants indoors. They have enormous experience with their plant type and they know exactly when to water the plant. So that is the case of a very skilled gardener compensating for a very bad soil. What gritty mix does for me is let me grow succulents outside in very abusive weather conditions, without the plant dying. A plant can get a week of rain and it will still drain well. During Summer, gritty mix will tolerate a bit of overwatering, although you still really need to pay attention to not overwatering. Whether you make your 511 mix with perlite/peat, or with two parts Turface, or with lava and pumice, is probably in the big picture not going to be the deciding factor in whether your plants grow well or not. Success can be add with any of those mixes because the size of the particles allows the roots to breathe and prevents capillary action of water from bring the perched water table to the top of the pot and drowning the roots. Fine-tuning how you make 511 is a question of matching the plant type to the moisture retention of the soil and to the watering habit and climate exposure. Any 511 variant is going to do better than almost any commercial potting soil because of the larger particles used in the majority of the mix.