For a windy urban corner that gets no shade, the best planter box is not simply the most attractive one. It needs weight, durability, drainage, heat tolerance, and a shape that will not easily tip over. The strongest all-around choice is a heavy-duty, UV-stable fiberglass or cast-stone planter with a wide, weighted base, a light-colored finish, and pre-drilled drainage holes. If weight is not a structural concern, cast concrete is excellent because it resists tipping and handles temperature swings well. For rooftops and balconies with load limits, commercial-grade fiberglass or reinforced resin is a better option because it is lighter but still tough.
Avoid thin plastic, lightweight metal, and unglazed terracotta in this exposure. Thin plastic can become brittle, fade, and blow over; metal can overheat roots in full sun; and terracotta dries out too quickly and may crack. A light gray, sand, or white planter is useful because it reflects heat and helps keep the root zone cooler. Good drainage is essential, so use a coarse, free-draining potting mix and make sure excess water can escape freely. A gravel mulch can reduce evaporation and add a little extra weight.
Size matters as much as material. Choose a planter at least 18 to 24 inches deep and 24 to 36 inches wide, or roughly 20 to 30 gallons of soil volume. This gives roots room to stay cooler and gives the container enough mass to resist wind. A square or rectangular shape with a low center of gravity is usually more stable than a tall, narrow pot. If the corner is very exposed, secure the planter with hidden anchor brackets, a weighted base, or a bolted-down tray. Do not rely on the plants alone to hold the planter down.
For planting, choose drought-tolerant, wind-tolerant, sun-loving species such as rosemary, lavender, ornamental grasses, sedum, yucca, agave where hardy, lantana, portulaca, and blanket flower. Avoid delicate broad-leaf plants and thirsty varieties that will struggle in constant wind and full sun. Group plants with similar water needs, and water deeply but less often to encourage strong roots. In winter or during extreme gusts, check the anchor and remove any damaged stems.
For most urban windy, full-sun corners, the best answer is a 24- to 30-inch square, light-colored, UV-stable fiberglass or cast-stone planter with reliable drainage and a wind-anchor kit. It is heavy enough to stay put, tough enough to handle sun, and large enough to support resilient plants.