1. Purchase an 6" or larger diameter planters pot from your local home improvement store. They run approximately $1 and if you can get the ones without holes it will save you a step.
2. If the pot has holes you'll need to cut a plastic bag to insert into it to keep the water from leaking out.
3. Place the plant stem or tree trunk in the center of the pot and stabilize it so it stays straight. You can use packing tape or duck tape over the top of the planters pot to stabilize the plant or trunk.
4. Fill the planters pot 2/3 full with Quickcrete post setting cement.
5. Pour enough water into the planters pot to soak the top layer of cement and leave about 1/4 to 1/2 inch of water on top.
That's it, now just let it set up and you have a weighted base that you can now use to set into your decorative container. This is by far the easiest and least messy method to use when potting non potted artificial plants and trees. So save some money and search for some non potted silk plants and trees and you can still make your home look beautiful for less.