Potting Mix - Is it worth Paying More?

Ever wondered why your potted plants or seedlings are not thriving?  It could be that your potting mix is to blame.
I did a bit of an experiment with some seedlings that I had far too many of.  These are Queensland Blue Pumpkins that I raised in foam boxes from seeds before potting them on.  We did not need 8 plants that is for sure.  So 4 of them were potted into Searles premium potting mix.  The other 4 were potted into a mix of cheap potting mix mixed with some good quality compost.  We use the cheap potting mix instead of synthetic kitty litter for our ageing cat which is why we had some on hand.
All the pots were watered the same amount and sat side by side in the shade house but look at the difference.
Well the proof is in the pumpkin in this case.  I suspect that the PH is way off and there is not enough organic matter to hold onto the moisture.

Look at those pitiful plants on the left.

 And no gardening is complete at our place without the number 1 garden helper.

Having a lie down after a big day in the garden

Have you had issues with cheap potting mix?