The short answer is: sometimes. There is no universal rule for urban planter boxes. Many modern plastic, resin, and fiberglass boxes are sold with drainage holes already drilled, or with removable rubber plugs and pre-marked knockout spots. Some self-watering models have a reservoir and an overflow hole instead of open drainage. Others, especially decorative metal, concrete, or ceramic-style boxes designed to protect balconies, patios, and floors, arrive completely sealed. So before you reach for a drill, flip the box over and inspect it.
Check the bottom and lower sides for small holes, rubber plugs, plastic caps, or dimples that look like drilling guides. Look for a removable tray, a false bottom, or an inner nursery pot. Read the label or instructions if you still have them. If the box has working holes or plugs you can remove, you usually do not need to drill. If it is a self-watering planter, do not drill into the main reservoir; just make sure the overflow hole is open so excess water can escape.
If the box is sealed, you will likely need to drill drainage holes yourself. This is common with decorative cachepots and inexpensive indoor planters. Without drainage, excess water collects at the bottom. That can lead to root rot, mold, fungus gnats, and a sour smell. Outdoors, standing water can also become a mosquito nursery. The exception is a planter designed for aquatic plants or a hydroponic system, where the water level is managed differently.
To drill, choose the right bit for the material. Use a twist bit or hole saw for plastic and resin, a wood bit for wood, a step bit for thin metal, and a masonry bit for concrete or stone. Mark four to six holes across the bottom for a medium box; add more for a long trough. A 1/4-inch to 3/8-inch bit is usually enough, though larger boxes may need 1/2-inch holes. Support the box firmly, drill slowly, and let the bit do the work. For brittle materials, place painter's tape over the spot first to reduce cracking.
After drilling, clean the holes and cover them with a small piece of window screen, landscape fabric, or a coffee filter. This keeps potting mix in while letting water out. Do not rely on a thick gravel layer to create drainage; it can actually raise the saturated zone. Instead, use a quality potting mix and make sure the box sits on feet or spacers so water can drain freely. If the box is indoors, set it in a waterproof saucer or use a nested pot system to protect surfaces.
If your urban planter box already has drainage holes, great, use them. If it has plugs, remove them for outdoor use. If it has a self-watering reservoir, follow the manufacturer's instructions and keep the overflow clear. If it is sealed and you want to grow conventional plants, drill holes before planting. In short, you may need to drill them yourself, but many urban planter boxes come ready with drainage or can be adapted with a few simple holes.