Controlling weeds in a rooftop farming setting requires a balance of prevention, manual removal, and possibly some organic methods to keep them at bay. Here are some easy methods you can employ:

1. Mulching: Covering the soil with a thick layer of mulch can suppress weed growth by blocking out sunlight and preventing weed seeds from germinating. Organic mulches like straw, wood chips, or shredded leaves work well.
2. Weed Fabric: Lay down weed fabric or landscape fabric before planting. This will block weeds from growing through while still allowing water and nutrients to penetrate the soil.
3. Regular Maintenance: Keep the rooftop farm area tidy by removing any weeds as soon as you spot them. This prevents them from establishing and spreading.
4. Hand Weeding: Pull out weeds by hand or with hand tools. Be sure to remove the entire root system to prevent regrowth.
5. Companion Planting: Planting certain crops together can naturally inhibit weed growth. Plants like marigolds, basil, and mint can act as natural weed suppressants.
6. Vinegar Solution: You can create a natural weed killer by mixing vinegar with a small amount of dish soap and spraying it directly onto the weeds. Be cautious when using this method as it can also affect nearby plants.
7. Boiling Water: Pouring boiling water over weeds can kill them effectively. Be careful not to pour it on desirable plants as it can also harm them.
8. Solarization: If possible, cover the soil with clear plastic sheeting during hot summer months. This heats up the soil and kills weed seeds and young weeds.
9. Raised Beds: If feasible, consider using raised beds for your rooftop farm. This makes it easier to control soil quality and weed growth.
10. Regular Inspections: Inspect your rooftop farm regularly for signs of weed growth and take action promptly to prevent them from spreading.

Remember to choose methods that are suitable and safe for your rooftop environment and the types of crops you are growing. Regular maintenance and vigilance are key to keeping weeds under control.