I am finding it difficult to locate a source for pine needles for my carnivorous bog. I can buy bundles of pine straw for $8 each. I read that pine bark also lowers pH when it decays. A bag of fine pine bark is only $4. Any thoughts?

Also, my bog is going to be around 18" deep; can I put a layer of sand at the bottom to take up some space so that I don't have to buy as much sphagnum peat?

Thanks, Bob