The difference between Pro mix BX (CHECK ON AMAZON) and the HP is that HP (CHECK ON AMAZON) contains more perlite (to help with better drainage & has low water retention ability) and no vermiculite, while BX has less perlite and extra vermiculite.
Additionally, the BX features some Bio-fungicide added, which the HP lacks. In other words, the HP would rain better, while the BX would store up more moisture for release when required.
So, if you live in a hot-dry area, then retaining moisture sounds logical, right?
ALSO SEE: Where To Get 20/25/30/40 Gallon Nursery Pots?
Pro Mix Bx Vs HP vs HP-CC vs Fafard
I’ve used them all, Fafard, HP, BX, HP-CC and I find the HP to be the best and most consistent. I have never needed to add in extra perlite or anything to it.
It dries out super well and I’ve gotten great root systems with it, too. I add Myco to the plug as soon as I sow my seed straight in. That typically helps me!
Want to grow under led? Then use the Pro Mix HP HIGH POROSITY (CHECK ON AMAZON). It is great for HPS or metal halide since it creates more heat so it could use the vermiculite to retain some water between feedings.
Keep your temps between 80-85 degrees for maximum uptake of nutrients when using for led grow lights. The RH should not be higher than 50% HPS ambient temp should be between 75 degrees and 78 degrees with a rh of no more than 50% have a great day.
The Pro-Mix HP w/Mycorrihizae has little more perlite than BX. My nursery supply features both and the HP costs more dollars but has more per bale.
However, my friends are happy with both so either is fine.
Sunshine and Fafard products are nice subsititutes for ProMix & BX. I have used for growing tomatoes, peppers, cucumbers, will give huge yields if you feed them exactly what they want.