Likely: your server/setup is using GP. Forestry can't plant or place water if it doesn't have permission in a claim. try /trust (forestry) but with brackets instead of parenthesis (my symbol button on my phone wont work...). You could also do public instead of forestry or remove it from a claim as a test.
Unlikely given it happens with trees too, but if its 1.47, put a water 'ring' around the outside of the planting area, the forestry in that version had trouble with placing water.
