Experts and BHG readers answer.
No. You can reuse the soil. Many people dump their containers each year so they don't have to deal with old roots entangled in the soil and old plant debris that may harbor disease. But you can easily reuse potting soil for several years. I like to mix in some new potting soil to help rejuvenate a depleted potting mix, so I find myself adding some new potting soil each year. And after several years, I do end up dumping the old stuff into the flowerbed and starting over fresh.