Short answer: You do not need a magical “special” soil, but you should not just dig up dirt from the park and dump it into an urban planter box. For most planter boxes, the best choice is a proper potting mix or raised-bed mix. These are lightweight, drain well, hold moisture, and give roots the air they need. Park dirt is usually compacted, low in organic matter, and may contain weed seeds, pests, diseases, and potentially pollutants from traffic, dogs, pesticides, or old buildings. Digging in a public park may also be illegal or harmful to the park.
Why potting mix works: Container roots are confined, so field soil compacts quickly in pots and reduces drainage and airflow. Potting mix contains ingredients such as peat moss, coco coir, bark, perlite, vermiculite, compost, and sometimes slow-release fertilizer. It stays loose, drains well, and still holds enough moisture. If your planter is a raised bed open to the ground, you can use native soil amended with compost and maybe perlite or sand. But for a true planter box on a balcony, patio, or rooftop, potting mix is much better.
Can you use park dirt? Technically, yes, if it is legal and you amend it heavily. A rough mix might be 50–60% park dirt, 30–40% compost, and 10–20% perlite. But this is risky. Urban soils can contain lead, arsenic, or other heavy metals, especially near roads, older buildings, or industrial sites. If you grow herbs, lettuce, tomatoes, or anything edible, do not use unknown park dirt. Use clean potting mix, tested topsoil, or raised-bed soil instead. Park dirt is also heavy. Wet soil in a large planter can become very heavy for balconies and roof gardens.
What to use instead: Buy potting mix labeled for containers. For vegetables, choose organic potting mix or raised-bed mix. Add compost for nutrients and perlite for drainage. Fertilize according to plant needs. Make sure the planter has drainage holes. Water consistently. If you want to save money, mix potting mix with compost and a little clean topsoil, but avoid park dirt. Test soil if you use any native or recycled soil, especially for edibles. So the answer is: no special magic soil, but yes, a suitable container mix. Park dirt alone is not a good idea. Use potting mix or a well-amended, clean raised-bed mix for healthier plants and safer food.