Quick Answer
To minimize moisture under a raised bed in wetlands, use a minimum of 6-8 inches of solid, well-draining materials like gravel, crushed stone, or decomposed granite, and ensure good drainage through the bed's bottom and sides.
Material Selection
Choose materials that allow for good water drainage while keeping the bed elevated. Incorporate a 2-inch layer of compacted gravel or crushed stone at the bottom, followed by a 4-inch layer of well-draining soil mix. Avoid using organic materials like wood chips or sawdust, which can retain moisture and create a humid environment.
Bed Design and Drainage
Ensure the raised bed has a slight slope (about 1:20) to promote water runoff. Install a French drain or a trench drain around the perimeter to collect and direct water away from the bed. This will help maintain a dry environment and prevent water accumulation.
Additional Tips
To further minimize moisture, consider adding a waterproof liner (like a durable plastic sheet) at the bottom of the bed. Plant species that thrive in wet environments but also have good drainage properties, such as succulents or cattails. Regularly inspect and maintain the bed to prevent clogging and ensure optimal drainage.
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