Ideally you want to keep water tables below the drip screed, stucco actualy sheds mositer through the screed metal at the bottom of the house (where plate line meets the slab). If you elevate your planter bed you should use a berrier against the house like a rubber membrane. You should also install a French drain against the house and below grade. Excess water will seep down that French drain and stay away from your house. I'd also paint that sedition before installing the membrane with elastic water proof paint.