>> I find the perlite lightens the mixture considerably & the vermiculite holds more water so it doesn't run through the sand & perlite. With the extreme heat we have here I need something to hold the moisture in the soil & the vermiculite does that well.
I agree that vermiculite holds water well. And vermiculite + Perlite provide more lightening and aeration than peat would.
If you buy a bag of bark mulch and screen out the biggest chunks and smallest powder, you might like replacing some or all of the Perlite in your soil mix with bark "grit" or small nuggets. Say, 1/16" and 1/8" and 3/16" ... up to to almost 1/4"
You can use bark nuggets a little larger than your Perlite as a 1-1 replacement for Perlite, because bark holds more water than Perlite for the same size granules.
Or, you could replace some of the vermiculite by using some finer bark (fibers and powder up to 1/16" as the water-holding ingredient. Any size vermiculite holds more water than bark, but very fine bark does hold a moderate amount of water (say, around half as much as an equal amount of peat moss).
Some fine bark + some gritty bark + some 1/8" + some 3/16" bark will keep the sandy mix "open" and aerated, but still hold some water.
And bark is cheaper than either Perlite or vermiculite, if you screen it yourself.
