It's impossible to say exactly what the white growth is without seeing it, but here are some of the most common possibilities for white growth under a deck on mulch:
1. Mold or Mildew: This is the most likely culprit, especially if the area is shaded and humid. Mold and mildew thrive in damp, dark environments.
2. Fungus: Various fungi can grow on mulch, especially if it's old or compacted. Some fungi produce white, fuzzy growths.
3. Salt Efflorescence: If you live in a coastal area or use de-icing salt in the winter, salt can be drawn up from the ground and form white, crystalline deposits on surfaces.
4. Effervescence from Treated Lumber: Some treated lumber contains chemicals that can leach out and create white deposits, especially if it's exposed to moisture.
5. Powdery Mildew: While primarily found on plants, this fungal disease can sometimes grow on mulch and other organic materials.
How to Identify the Cause:
* Appearance: Look closely at the white growth. Is it fuzzy, powdery, or crystalline? Does it have a distinct odor?
* Location: Is the growth concentrated under the deck or spread out?
* Weather Conditions: Have you had recent rainfall or high humidity?
* Materials: What kind of mulch are you using? Is your deck made of treated lumber?
How to Get Rid of the Growth:
* Clean and Dry: The best way to prevent mold and mildew is to keep the area clean and dry. Rake away any excess mulch and ensure good drainage.
* Ventilation: Improve air circulation by trimming back any overhanging branches or shrubs.
* Bleach Solution: For mold and mildew, you can use a bleach solution (1 part bleach to 10 parts water) to clean the affected areas. Be careful not to get bleach on plants or other surfaces.
* Fungicide: For fungal growths, a fungicide can be effective. Choose a product that is safe for use around plants and follow the label instructions carefully.
Prevention Tips:
* Choose a well-draining mulch: Avoid compacted or water-retentive mulches like wood chips or pine straw.
* Space mulch away from structures: Leave a gap between the mulch and your deck to allow for air circulation.
* Regularly clean and maintain: Sweep away debris and remove any fallen leaves or branches promptly.
If you're unsure about the cause of the white growth, it's always best to contact a professional for help.
