Determine how high you want your pot tower. Get enough pots, either in graduated sizes or the same size, to reach your chosen height. Buy a piece of rebar that equals your pot stack height plus 24 inches. Leave enough room for planting when sizing your pots. The inside diameter at the top of a pot should be 4 to 6 inches wider than the bottom of the pot you will stack in it.
Buy enough potting soil to fill all the pots. For instance, using a 20-inch standard pot for the stack bottom, you'll need 28 quarts of potting soil to fill it. Get enough coarse gravel to make a 1-inch layer in the bottom of each pot for drainage.
Choose plants for the containers. Check the plants' information tags before you buy for mature sizes to be sure they won't overgrow their containers. Find out what plants are evergreen in your climate if you want year-round interest.
Pick a place in your garden for the stacked planter set. Clear and level the spot by stripping off any sod, then blading or raking the ground smooth.
Put a piece of duct tape just above the 24-inch mark on your piece of rebar. Center the first pot on your site and drive the rebar into the ground through the drainage hole. Stop when the duct tape touches the hole.
Put a 1-inch layer of gravel in the pot and fill it with moistened potting soil to within 2 inches of the lip. Firm up the soil as you go to make a solid base for the next pot. Stack the next pot on top of it by threading its drainage hole over the rebar. Continue to fill and stack pots till you have them all stacked.
Use a trowel to plant your chosen annuals, perennials or evergreens. Finish by watering each pot thoroughly, beginning with the top container.