No, you do not need special soil for self-watering planters. Any quality potting compost can be used successfully in self-watering pots. If you work in a handful of homemade compost it can boost the nutrient levels in the soil, and also consider implementing a small amount of slow release fertilizer into the soil mix. Never reuse garden soil in pots or containers as it can hold far too much water and cause potential root rot in plants.