I mainly plan on only using one soiless mix this year.

The 'recipe' I use is below....

2-3 cubic feet pine bark mulch
5 gallons perlite
5 gallons peat moss

2 c time-release fertilizer (that's designed for container gardening; I mix osmocote directly into the mix when I make it)

I want to make a minor adjustment to the above recipe.

Can I add a small amount of compost to the above mix, without it adversely affecting drainage? It's namely for
root veggies, (which I've noticed from growing them in containers....this is based on past experience) prefer a mix with a little compost in it and for heavy feeders (melons, squash, cukes, zukes).

One lg. batch of the above mix yields 30-35 gallons; I would be adding 10%-20% compost per batch (10% of this for a large batch would be 3 to 3-1/2 gallons per lg. batch; 20% for a large batch would be 6-7 gallons).