I’d tackle this in two layers: stop the mess from landing on the furniture, and make whatever does land easy to remove. First, look up. If your chairs or table sit under a tree, balcony ledge, or roosting spot, move them a few feet or add a patio umbrella or canopy. In a rental or shared building, ask before pruning branches, but even trimming back overhang with permission can cut sap drip and bird traffic. Don’t feed birds nearby, and keep ledges—not furniture—as the place for humane deterrents such as bird spikes, netting, or reflective tape.
For furniture you don’t use daily, a fitted waterproof cover is the simplest shield. Choose one with straps or elastic, vents to reduce condensation, and a smooth outer fabric that bird droppings and sap don’t grip. Shake and wipe the cover before you remove it, and wash it according to the label. Cushions should be removable and washable, and during messy seasons I’d store them in a deck box or indoors. An outdoor rug under the seating area also makes cleanups easier and keeps droppings off the patio surface.
Treat the furniture itself, too. Seal wood with an outdoor-rated sealer, wax metal frames, and use a manufacturer-approved protectant on resin or composite pieces. Test any product on a hidden spot first. For tree sap, don’t smear it; let it harden, scrape it gently with a plastic card, then use a little isopropyl alcohol or a citrus-based adhesive remover on durable surfaces—never on delicate fabric. Bird droppings are acidic, so wipe them up promptly with a damp cloth and mild soapy water, then rinse and dry. For fabric, blot first and use an outdoor fabric cleaner rather than bleach.
A quick weekly routine makes a big difference: cover furniture after use, bring cushions in, wipe frames, and check under trees after wind or rain. If sap is a constant problem, consider a dedicated sap-resistant cover or reposition the seating altogether. With a little planning, you can keep your urban outdoor space usable without waging war on the birds.