Crops grow on any node with soil=3 group set to be compatible with other mods.

init.lua

@@ -1,5 +1,5 @@
 --[[
-	Minetest Farming Redo Mod 1.22 (31st March 2016)
+	Minetest Farming Redo Mod 1.22 (24th May 2016)
 	by TenPlus1
 	NEW growing routine by prestidigitator
 	auto-refill by crabman77
@@ -420,9 +420,9 @@ function farming.plant_growth_timer(pos, elapsed, node_name)
 			return true
 		end
 	else
-		local under = minetest.get_node_or_nil({ x = pos.x, y = pos.y - 1, z = pos.z })
+		local under = minetest.get_node({ x = pos.x, y = pos.y - 1, z = pos.z })
 
-		if not under or under.name ~= "farming:soil_wet" then
+		if minetest.get_item_group(under.name, "soil") < 2 then
 			return true
 		end
 	end