Dwarf varieties of annual phlox do very well in windowboxes, planters and tubs. For containers, sow seeds indoors 4 to 6 weeks before setting outside. Space new plants about 6 inches apart. You can plant 3 or 4 seeds per 4 or 5 inch pot and transplant in 6 to 8 weeks as a clump. Keep plants in containers well watered. Those in terra cotta containers may need to be watered twice a day during especially hot days in the summer.