Cats are creatures of habit and repeatedly visit the same spot to urinate and spray. Once a cat smells another in the same area, it might spray again to remove the scent of the strange animal. The fresh air helps dilute the smell, but you'll still pick up traces of the scent lingering in the area. Removing the cat urine smell with household products also keeps the cat from urinating in that same area.
Shine a black light over the flower beds at night and look for the urine soaked areas. The proteins in the cat urine turn a bright white while under a black light.
Dilute the urine by spraying with a garden hose that has a spray nozzle attached. Spray all over the flower bed, but focus specifically on the areas you identified while using the black light. This helps break down the cat urine and reduce the smell.
Combine one part vinegar with two parts water in a spray bottle. Spray the solution directly on the urine soaked areas of your flower beds and rub into the dirt with your hands. Alternatively, pour the solution directly onto the flower beds, as it won't harm the flowers.
Clean any concrete decorations in the flower bed or concrete or wood borders with the same vinegar and water solution. Pour the solution directly onto the affected areas and rinse away with fresh water after 10 minutes.
Apply more of the solution if you notice the urine smell lingering. Keep a bottle on hand and apply directly to the flower beds if cats continue urinating in the area. The harsh scent of the vinegar should repel the cats and keep the animals from urinating in the space.