raised garden beds
How to build one that can be used for years without using womanized wood
Greene County Pennsylvania
Use naturally resistance lumber such as cedar if available and not cost prohibitive.
or you can use a product such as composite decking (found at most lumber suppliers) made from recycled plastics. It is very heavy but will last a long time without decay.
Alternately, you can construct using product like concrete or concrete aggregate like gunite (light-weight, fibre and concrete mix [some pools are constructed with this material]).
Hope this helps.