A plastic pot if you can find one to fit would be great. Otherwise, I would use black landscape plastic.
store bought liners,plastic pots,plastic bags,sphagnum moss,fabric,burlap; really depends what your plant is if it needs no soil-like orchids,epiphytes, dryer soil with complete drainage,or really moist soil less drainage and where you live --do you live in hot dry climate(use something that retains water-like plastic) or really wet rainy humid area need better air circulation and drainage(use something like fabric,burlap, sphagnum moss).
Thank you for your reply which was helpful these are two, different sized, Victorian conservatory Wicker basket on the leg is about 3 foot tall my problem is I cannot get plant pots of the right size and I didn’t want to rot the baskets and brown plants that I put in them which will go outside my front door
A black contractors trash bag. The plastic is thick enough to hold everything without leaking. Line the bottom with stones and activated charcoal. Use a piece if landscape fabric to line the area above stones bottom and sides. Fill with soil and plant. Trim the bag and landscape fabric and fold under around top of basket. Use moss to cover the soil around plants.
Thanks everyone they are Victorian conservatory Wicker baskets on legs about 3 foot tall and obviously I don’t want to damage them but equally I didn’t want to drown the plants. Unfortunately they are two different sizes and getting pots to fit is proving very difficult, that would obviously have been my best answer to the problem
I like this basket liner (click here for shopping link) I've cut it to fit baskets and even an old wagon I filled with plants.