Soil for potting up market seedlings
 

This year is my first year selling seedlings. I used CDPM (Craig's Dense Planting Method) with great success and potted about 900 seedlings in Pro Mix in 3.5" square tall pots. When some of the plants started to look sad from insufficient root space, I potted 300 of them up into 6" round pots with a MG potting mix + peat + vermiculite mix. I didn't have enough big pots for all of them, so the ones that stayed in the small pots got topped off with that mix (there had been about an inch of space from the soil to the pot rim).

Along the way, I have removed the lower stems of all plants (both in the 3.5"s and the 6"s to improve airflow and minimize disease).

Also, I planted about 60 of these seedlings in new raised beds for myself about 3 weeks ago. The beds have a mix of mushroom mulch, peat and vermiculite. They received similar water, sun and the same 3 applications of liquid MG that I gave the seedlings still in the pots.

Observations: The plants in the bigger pots look about the same in height and health (all good) as the ones still in the smaller pots. However, these potted seedlings are all lined up next to my raised bed tomato plants, and the raised bed plants are a good 3 times bigger than the potted seedlings.

Questions: What is it about the mushroom mulch / raised beds that is driving the plant growth?

If I want to sell larger seedlings (for more $$) earlier next season, should I skip the MG mix and go with the homemade mushroom mulch mix? I know that I should use a sterile mix to avoid damping off, so I'm thinking that I would take the young seedlings from CDPM and put them in Pro Mix in the 3.5" pots (since I have a bunch left), then pot up into 6" or even gallon pots with the mushroom mulch mix. Extra work, but worth it to be able to sell bigger plants sooner.

Thoughts or suggestions?