Weeds can be a nuisance in any garden, but they can be especially difficult to control in flagstone gardens. The cracks and crevices between the stones provide perfect places for weed seeds to germinate and take hold. Fortunately, there are a few things you can do to keep weeds from becoming a problem in your flagstone garden. One of the best ways to prevent weeds is to apply a pre-emergent herbicide before they have a chance to sprout. Pre-emergent herbicides work by creating a barrier on the surface of the soil that prevents weed seeds from germinating. Be sure to apply the herbicide evenly over the entire area where you plan to install flagstones, as well as any areas where weeds are already a problem. Another way to prevent weeds is to install a weed barrier beneath the flagstones. Weed barriers are sheets of heavy-duty plastic or landscape fabric that prevent light and water from reaching the soil below. This makes it difficult for weed seeds to germinate and grow. Weed barriers should be installed before you lay the flagstones, and they should extend at least a few inches beyond the perimeter of the stone area. Once weeds have already taken root in your flagstone garden, they can be difficult to control. Hand-pulling is often the best option, but make sure to get the entire root so that the weed doesn't simply regrow. You can also use a sharp hoe or trowel to carefully cut the weed off at ground level. Be careful not to damage the flagstones when using these tools. In some cases, it may be necessary to use chemical herbicides to control weeds in your flagstone garden. These products can be effective, but they should be used as a last resort and only as directed on the label. Some chemicals can also damage helpful plants and insects, so it's important to choose one that is specifically designed for use around flagstones.