That's an excellent and very important question! Proper drainage is one of the most critical factors for the health of your plants, and it's smart to be thinking about it.
To answer you directly: Yes, virtually all quality urban planter boxes designed for live plants absolutely must have drainage holes in the bottom. This is non-negotiable for plant health. Without an escape route, excess water pools at the bottom of the planter, saturating the soil.
Why is this so crucial? When soil becomes waterlogged, it drives out vital air pockets that roots need to breathe. This creates an anaerobic environment, leading to a condition called "root rot," where the roots essentially drown and decay. This will quickly kill most plants, from herbs and flowers to vegetables.
If you fall in love with a container that lacks holes, such as a certain decorative pot, you have a couple of options. The simplest is to use it as a "cachepot" or cover pot. Place your plant in a standard, hole-equipped nursery pot and then set that pot inside the decorative one. Just remember to empty the outer pot of any drained water after watering. Alternatively, for materials like wood or fiberglass, you can carefully drill your own holes.
For planters that do have holes, using a shallow layer of drainage material like pebbles or pumice at the bottom can help prevent soil from washing out while still allowing water to flow freely. Ultimately, those little holes at the bottom are your plant's lifeline, ensuring a perfect balance of moisture and air for a thriving urban garden.