-Needs to be inside, with a roof
-Not much light
-not too close to another schlump
-house made of wood or brick
If they are not in the right environment, they will disappear unless you pick them back up with the jar immediately. They are quite small at the start and hardly give you anything. But when you leave it for a while it starts growing a giving you better gifts every time it grows. If a shlump has two small heads coming out of his shoulders that means he is grown fully.
Schlumps can be very useful as they drop random items.