So you want to tie the solution to the category, not to the item in the category? Let's say pine needles need product range X. If you want to display suitable products on the pine needle page, you could store "product range X" as a custom field in your CPT, and use that to drive displaying products from product range X on that page. What I'm saying is, use taxonomy to organise your content, but not necessarily to drive the recommended solution. That allows you flexibility in the future, if you later find an exception, like the day you meet semi-deciduous trees :-) .