PLANT PLACEMENT Feel free to get creative — there are no hard-and-fast rules. That said, for a foolproof composition, follow this traditional scheme: Place tall, spiky grasses in the back, trailing varieties at the front and sides, and fill the middle with bushier plants.
SOIL Tempting as it may seem, don't just dig up dirt from your backyard. Instead, go with a medium-weight potting mix that includes perlite and vermiculite — minerals that help keep the soil aerated and prevent water loss.
WATERING If it hasn't rained, expect to water most boxes at least once a day (if your flowers start to droop or the soil feels dry half an inch below the surface, you'll need to up the frequency). Soak the plants completely until excess liquid runs out the drainage holes.
FERTILIZER Because most soil mixes don't provide enough nutrients, fertilize your plants with a water-soluble formula such as Schultz Bloom Plus