Spring planting in a city calls for a little prep before you add seedlings. Start by emptying the planter box and removing old roots, dead leaves, and compacted soil. Scrub the inside with warm soapy water if it is empty and rinse well; if the box is lined, check that the liner is intact and that excess water can still escape. Confirm drainage is working: clear clogged holes, add a layer of coarse material only if your box lacks drainage, and make sure the planter sits slightly off the ground or balcony surface so water can flow away.
Next, refresh the growing medium. Urban containers often become compacted and depleted after a season. Replace at least the top third to half of the old soil with a light, high-quality container mix, and mix in well-rotted compost or slow-release organic fertilizer according to the label. Avoid garden soil straight from the ground, because it is heavy, drains poorly in containers, and may contain weed seeds or pollutants. Fill the box loosely to about 2–3 cm below the rim, then firm it gently—not tightly—and water until it drains evenly. Let it settle before planting.
Check the site before you choose plants. Most vegetables and flowers need six to eight hours of direct sun, but balconies can be windy, hot, and shaded by buildings. Place the box where it will receive reliable light and be easy to reach for watering. If weight is a concern, use lightweight mix and raise the box on castors or sturdy feet. Pre-moisten the soil, then set seedlings at the same depth they grew in their pots, spacing them according to their mature size. Water again after planting, add a thin layer of mulch if the surface dries quickly, and keep an eye on moisture during the first week. With clean drainage, fresh soil, and a sunny, sheltered spot, your urban planter box will be ready for a strong spring start.