That's an excellent and crucial question for any urban gardener. The answer isn't a simple yes or no, as it depends entirely on the type and design of the planter box you purchase.
Many modern urban planter boxes, especially those designed for balconies and patios, do come with pre-drilled drainage holes. This is particularly true for functional, plant-focused containers made from materials like resin, plastic, or fiberglass. Always check the product description or specifications before buying; phrases like "built-in drainage," "drainage plug," or "overflow hole" indicate they are included.
However, some stylish or multi-purpose boxes—often those made from sealed wood, metal, or designed as decorative troughs—may not have holes. This is to preserve their material integrity, prevent rust, or allow for flexible use (like holding utensils or dry items). In these cases, you will need to create drainage yourself.
How to Add Drainage Holes Yourself:
If your planter lacks holes, you can easily add them. For plastic or thin metal planters, use a power drill with a standard drill bit. For ceramic or thick pots, use a masonry bit and drill slowly with light pressure. Always place a piece of tape over the spot you're drilling to prevent the bit from slipping. Aim for several small holes (about 1/4 to 1/2 inch in diameter) in the bottom.
A Key Alternative: The Double-Pot Method
If drilling isn't an option, use the double-potting technique. Place your plant in a standard plastic nursery pot (which has holes) and then set that pot inside the decorative, hole-less planter box. Simply lift the inner pot to drain excess water after watering. This method also protects the outer planter from moisture damage.
Special Note on Self-Watering Planters:
Many "self-watering" or "sub-irrigation" planters have a different system. They often feature a built-in water reservoir at the bottom, separated from the soil by a platform. These planters typically have an overflow hole on the side to prevent overfilling the reservoir, not traditional bottom holes. They do not require drilling.
In summary, always verify the product details. If drainage holes are absent, you can usually add them with a simple DIY step or use a nursery pot insert. Proper drainage is non-negotiable for plant health, as it prevents root rot by allowing excess water to escape.