PVC Pipe Planter Disney world does this! Lowes sells the 4 to round PVC pipe with holes already drilled. Purchase an end cap, fill with rock, soil, and plant. I will often put these in the center of a very large pot to stabilize, and add amazing heigh
Cut the bottom off a plastic pot to contain invasive plants & bury in the ground, works great for containing plants that tend to spread. Use a larger pot so that the plant can spread it's roots and grow deeper roots. Great for bamboo!
building raised garden beds--Gives you every single material and all the tools you'll need, and step by step directions. HIGHLY reccommend using this if you're thinking about building raised garden beds.
Budget & Small Space Friendly: DIY Cinderblock Planters