diff --git a/farm_control.lua b/farm_control.lua
index ae9abb8..5c9b459 100644
--- a/farm_control.lua
+++ b/farm_control.lua
@@ -39,7 +39,11 @@ function check_levels (levels, src)
     local needs_farming = {}
     for item, data in pairs(levels) do
         if amounts[item] ~= nil and amounts[item] < data[1] then
-            table.insert(needs_farming, data[2])
+            if data[2] ~= nil then
+                table.insert(needs_farming, data[2])
+            else
+                table.insert(needs_farming, true)
+            end
         end
     end
     if needs_farming[1] == nil then
@@ -66,19 +70,31 @@ function send_machine (relay_and_side)
     peripheral.call(relay, RELAY_COMMAND, side, false)
 end
 
--- TODO make a different loop for crops controlled by a CLI arg
--- the other loop doesn't need to load the harvester, but also doesn't need
--- to send the harvester unless stock drops below a level
-while true do
-    local needs_farming = check_levels(LEVELS, STORAGE)
-    if needs_farming ~= nil then
-        for _, item in ipairs(needs_farming) do
-            load_stack(item, STORAGE, PLANTER)
+-- if the first argument to this program is "replant", a separate machine will
+-- be sent out to replant crops between harvests
+if arg[1] == "replant" then
+    while true do
+        local needs_farming = check_levels(LEVELS, STORAGE)
+        if needs_farming ~= nil then
+            for _, item in ipairs(needs_farming) do
+                load_stack(item, STORAGE, PLANTER)
+            end
+            send_machine(PLANTER_RELAY)
+            os.sleep(SLEEP_TIME)
         end
-        send_machine(PLANTER_RELAY)
+        send_machine(HARVESTER_RELAY)
         os.sleep(SLEEP_TIME)
+        pull_items(HARVESTER, STORAGE)
+    end
+-- otherwise, the harvester will just be sent out when a crop's levels drop too
+-- low
+else
+    while true do
+        local needs_farming = check_levels(LEVELS, STORAGE)
+        if needs_farming ~= nil then
+            send_machine(HARVESTER_RELAY)
+        end
+        os.sleep(SLEEP_TIME)
+        pull_items(HARVESTER, STORAGE)
     end
-    send_machine(HARVESTER_RELAY)
-    os.sleep(SLEEP_TIME)
-    pull_items(HARVESTER, STORAGE)
 end