I will be planting blueberries in 18 inch tall 4x8 raised beds. I plan to use this as my basic soil: (pH 6-6.5) 30% Native Screened Sandy Loam 40% Garden Compost 5% Power Mulch 5% Mushroom Compost 20% Horticultural Pumice. How can I transform this basic soil to make it perfect for blueberries? I am thinking of taking the basic soil and combining it with equal parts douglas fir bark. Or do you think I should leave the basic soil as it is and just add sulphur? Or something else... what is the perfect soil to place in the raised beds?