Not only is bleach corrosive and harmful to plants it comes into direct contact with, it will most likely kill them completely. Often, a pressure washing company uses bleach to remove microorganisms, such as mold and mildew. This solution must be diluted properly so that it does not cause damage to plants. Some chemicals used with pressure washers can kill plants, but there are safe chemicals you can use when pressure washing.
Chlorine bleach harms plants, while oxygen bleach doesn't. If you need to pressure wash to solve a moss problem, you can find products that only treat moss and keep plants safe. You can find effective pressure washing chemicals that don't harm plants. Check the label and look for warnings to determine if a product is safe or can kill plants.