Start by giving your summer annuals a gentle exit. If any are still healthy, move them to another pot or compost them. Pull out spent plants, roots and all, then shake loose soil from the root ball. Remove weeds, fallen petals, and any pests hiding near the rim.
Next, refresh the soil in your urban planter box. You do not need to replace everything. Take out the top 2–3 inches of old potting mix and replace it with fresh, quality container mix. Mix in a slow-release fertilizer or compost to recharge nutrients. If your box is small, consider replacing most of the soil to avoid disease buildup.
Choose fall mums that suit your space. Garden mums are budget-friendly and come in bronze, burgundy, gold, pink, purple, and white. For a longer show, look for early, mid, and late-season varieties. Before planting, water the mums in their nursery pots and loosen the roots slightly. Set them at the same depth they were growing, spacing them 6–10 inches apart so air can move.
After planting, water thoroughly until it runs from the drainage holes. Keep the soil evenly moist but not soggy; urban boxes dry out fast, especially near concrete or metal. Add a 1–2 inch layer of mulch, such as shredded bark or straw, to hold moisture and keep roots cool. Deadhead spent blooms and pinch back leggy stems early to encourage more flowers.
As fall deepens, protect your mums from frost. Move the planter box to a sheltered spot, or wrap it with burlap if nights get cold. Water less often but do not let the soil go bone dry. With a little refresh and regular care, your urban planter box can shift smoothly from summer color to a crisp autumn display of mums.