The short answer is to combine a low, heavy base with a positive connection to a solid structure—or use enough approved ballast if drilling is impossible. A planter that is simply heavy can still slide or tip if the wind gets under the foliage or the sides act like a sail, so think in layers: weight, friction, and anchorage.
First, assess what you are anchoring to. If the planter sits on concrete, stone, or brick pavers, you may be able to use expansion anchors or concrete screws. If it sits on a balcony with a waterproof membrane, do not drill blindly. Check with the building owner, HOA, or a contractor. For decks, use stainless-steel or hot-dip galvanized hardware and seal every penetration to prevent rot or water damage.
For a drillable hard surface, empty the planter or at least remove the soil around the base. Mark the mounting holes through the planter's pre-drilled feet or add two or four L-shaped brackets inside the base. Drill the correct size for your anchors, vacuum the dust, and set concrete screws or sleeve anchors. Bolt the brackets to the surface and the planter to the brackets. Use washers and nylon lock nuts so vibration does not loosen them. If the planter has wheels, remove them for the storm or lock them and add fixed chocks; wheels are a common tipping point.
If you cannot drill, use ballast. Line the bottom with paving stones, sandbags, or concrete blocks. Keep the weight as low as possible and distribute it evenly. A good rule of thumb is that the ballast should be at least as heavy as the fully planted, wet planter, but wind exposure, height, and shape matter more than a single number. Make sure the planter still drains. A soggy, anaerobic root zone will kill plants, and trapped water adds unstable weight.
Then add a structural tie-down. Thread rated stainless-steel cable, a ratchet strap, or a heavy-duty nylon strap through the planter's integrated anchor points or around its strongest lower frame. Connect it to a wall stud, a structural column, a rated railing post, or a ground anchor—not to a loose handrail, a downspout, or a thin balcony panel. Use eye bolts, turnbuckles, and shackles rated for outdoor use. Leave a little slack for movement, but not enough for the planter to rock. If you tie multiple planters together, treat that as a supplement, not a substitute for anchoring to a building or ground.
For very exposed roofs, terraces, and street locations, consider a custom ballast tray or a steel base plate bolted to the planter and then weighted with pavers. In public spaces, never drill into sidewalks or attach to street furniture without permission; contact the city or property manager. They may require engineered drawings or rated temporary ballast.
Finally, prepare before the storm. Move lightweight planters indoors or into a sheltered corner. Trim tall, top-heavy plants, and choose low-growing, wind-tolerant species for exposed spots. Water before a storm only if the soil is dry; saturated soil is heavy but can make the planter top-heavy and unstable. After the storm, check anchors, straps, brackets, and drainage. Replace rusted hardware and re-tighten loose bolts. The goal is not to make the planter immovable forever—it is to make it predictable, stable, and safe when the wind tries to push it over.