you can use if conditions, and a self or entity property (or a global property, but it's probably better to use self or entity property..)
for self property
if self.property["grown"] == false then
return // replace return with code
else
return // replace return with code
end;
for entity property
if entity["farmland1"].property["grown"] == false then
return // replace return with code
else
return // replace return with code
end;
And you can do have if conditions inside of if conditions.
Edit: Keep in mind, you need to create the property on the object, entity, or tile in question. Which you can do in your voxel editor, to automatically add the property in, when you place the entity, or you can do it individually in the map editor, when you select the entity.