For a start you would need to get some goodness into the soil, conifers are greedy feeders and will have deplenished the soil. Add some compost and some Bonemeal when you plant. To be absolutely certain of the soils acidity/alakalinity (pH) you really would need to buy one of those cheap Soil testing kits and follow the info on the packet. It tells you how much lime to add if need be to bring the soil up to the level you require.