If you see white, powdery-looking stuff on the outside of your pot, don't freak out.  It's not the infamous "powdery mildew" you might hear about in grower circles. It's not mold.   It's just efflorescence.   The soil is full of salts, minerals and nutrients.  When you water, the water will carry (or "wash away") some of these elements when it runs out of the sides of the cloth pot.  In doing so, the cloth fabric of the pot acts like a filter of sorts and "catches" some of the salts and minerals that get trapped in the fabric and stay behind as the water itself runs off or evaporates.  There's a short demonstration video available here that explains this phenomenon.  It might appear a little "dirty" or unsightly, but it's normal and perfectly fine.