The Problem

Expected that crop growth block HANGING mangrove propagules from growing.

A Solution

Add mangrove propagules to this flag

Alternatives

Create a separate flag, that prevents growing of those.

Anything Else?

Since this is kinda a sapling and has a hanging and not hanging variant iam not sure which type it fits more.
Crop or sapling

they are most certainly saplings - they belong to the sapling tag already, and as far as i know grow in the same way as saplings (ie via structuregrow, into trees). i see no compelling argument to designate these as crops instead.