The porous nature of wood allows moisture to sit on it for long periods of time. This in turn encourages mould and mildew growth. While many commercial cleaners will remove mildew, they may also damage plants that are growing on or near the fence.
Many commercial mould and mildew cleaners contain bleach, which will burn the leaves of delicate plants. While it's possible to protect some plants by covering them before you use the cleaning solution, plants that grow directly on the fence cannot be completely protected. Instead, use a plant-friendly mildew remover.
White vinegar, tea-tree oil and grapefruit-seed extract are all natural materials that will kill mould or mildew and will not harm your plants. In addition, liquid dish-washing detergent, which does not foam, will help you scrub off the mildew.
White vinegar is the least expensive all-natural ingredient listed in section 2, and many homeowners already have it in their kitchen cupboards. Fill a spray bottle with straight white vinegar and spray it directly on the mildew. Let it sit for about 20 minutes. Then, mix a squirt of liquid dish-washing detergent with water in a bucket, and use that solution to scrub off the mildew. If you want to use tea-tree oil, which kills all mould and mildew (as opposed to vinegar, which kills 82 per cent), combine 2 tsp with 2 cups of water. The recipe for grapefruit-seed extract is 20 drops with 2 cups of water.