diff --git a/mods/bg_tree/grow_sapling.lua b/mods/bg_tree/grow_sapling.lua
index f9e53c5..1d3a948 100644
--- a/mods/bg_tree/grow_sapling.lua
+++ b/mods/bg_tree/grow_sapling.lua
@@ -9,8 +9,10 @@ local leaves_growing = modname .. ":leaves_growing"
 
 
 local function supports_sapling (name)
-	if name == log_alive or name == root_alive then return true end
-	return minetest.get_item_group(name, "dirty") > 0
+	return blockgame.item_matches(name, {
+		"group:supports_sapling",
+		"group:dirty",
+	})
 end
 
 -- this commented-out function will be used when roots start affecting tree growth.
@@ -39,7 +41,7 @@ blockgame.register_increasing_abm({
 	id = modname .. ":grow_sapling",
 	label = "grow sapling",
 	nodenames = {sapling},
-	neighbors = {"group:dirty", log_alive},
+	neighbors = {"group:supports_sapling", "group:dirty"},
 	interval = 15,
 	chance = 4,
 	rate = function (pos, node, data)
diff --git a/mods/bg_tree/node.lua b/mods/bg_tree/node.lua
index c79947e..33ca3f3 100644
--- a/mods/bg_tree/node.lua
+++ b/mods/bg_tree/node.lua
@@ -19,6 +19,7 @@ blockgame.register_node("root_alive", {
 	description = "Growing Root",
 	groups = {
 		woody = 1,
+		supports_sapling = 1,
 	},
 	drop = modname .. ":root",
 })
diff --git a/mods/bg_tree/node_log.lua b/mods/bg_tree/node_log.lua
index 421d947..ba522be 100644
--- a/mods/bg_tree/node_log.lua
+++ b/mods/bg_tree/node_log.lua
@@ -28,6 +28,7 @@ reg_log("log", {
 reg_log("log_alive", {
 	groups = {
 		planty = 1,
+		supports_sapling = 1,
 	},
 	texture = "log",
 	drop = modname .. ":log",