Hi, thanks for the add ❤️ I recently bought an Acer and a Rhododendron not knowing they needed to be in ericaceous soil, my acer seems to be coping well (has even grown new leaves) but the rhododendron looks dry and hasn't grown at all (it's in a half barrel with 100lt compost), what's the most effective (and cheapest if poss) way to go about making the soil more acidic please? At the moment they're both in multipurpose compost.