Yes, you can grow root vegetables like carrots in a shallow urban planter box, but success depends on how shallow the box really is and which varieties you choose. Carrots are root vegetables, so they need loose, stone-free soil and enough depth for the edible root to develop. If your planter box is only 4–6 inches deep, carrots will struggle and are likely to be small, forked, or stunted. In that case, it is better to grow radishes, salad turnips, scallions, or other shallow-rooted crops.
For carrots in a shallow urban planter box, aim for at least 8–10 inches of soil depth, and 12 inches is even better for medium-size carrots. Choose short or round carrot varieties such as Paris Market, Little Finger, Amsterdam, or Chantenay. These types are much more forgiving in containers than long, tapered carrots. Fill the box with loose, well-draining potting mix, avoid fresh manure, and remove stones or clumps that can cause deformed roots.
Sow carrot seeds directly into the planter box, keep the soil evenly moist until germination, and thin the seedlings to about 2–3 inches apart. Consistent watering is important because dry spells can make carrots woody or split. Place the box in full sun, and harvest when the roots reach a usable size. With the right depth, variety, and care, a shallow urban planter box can produce a useful crop of carrots and other compact root vegetables.