The downsides to using landscape fabric in your garden are many. Soil accumulates on the top, which eventually supports weed growth anyway. Provided that you use the best type of landscape fabric, you should find that it brings several benefits to the installation of your new shed. But when you throw a heavy-duty landscape fabric into the mix, it makes life very difficult indeed for even the most recalcitrant weeds. The trick is to use commercial-grade landscape fabric — the heavier duty, the better.