I usually mix my own potting mix as required in batches of 50 litres using a concrete mixer to blend the ingredients of composted hammermill pine bark,coarse washed quartz sand,perlite,dolomite and an 8/9 month slow release fertilizer. This mix is a basic one for both herbaceous perennials,bulbs/corms as well as seeds and I usually have good results for all of these plants. Last August I was potting up Helleborus x hybridus seedlings and had a lapse of concentration which was not noticed until some weeks later when the potted seedlings started to grow,some 1200 tube pots were done at the same time and one of the mixer loads slow release fertilizer was accidentally omitted.The resultant seedlings without fertilizer are now barely half the size of the fertilised potted plants.I will hopefully not do this again.Some years ago I was buying premixed potting mix in 1 cubic metre batches and results were so poor I started to mix my own,much more effective and economical.This is in Tasmania where Winter frosts are -3 C to -4 C degrees and Summers can reach low to mid 30C,hottest was a couple of years ago when disastrous bush fires hit many parts of mainland Australia.Gordon Julian