Raised Bed Soil Calculator

Complete Guide to Raised Bed Soil

Understanding Soil Mixes

Mel's Mix (Square Foot Gardening)

The gold standard for intensive vegetable gardening, created by Mel Bartholomew. This mix provides excellent drainage, moisture retention, and nutrients:

• 1/3 Peat Moss or Coir: Retains moisture while providing good drainage
• 1/3 Vermiculite: Improves aeration and holds nutrients
• 1/3 Blended Compost: Provides nutrients from multiple sources

Budget-Friendly Alternatives

While Mel's Mix is excellent, it can be expensive for large beds. Consider these alternatives:

• 60/30/10 Mix: 60% topsoil, 30% compost, 10% perlite or sand
• 50/50 Mix: Equal parts topsoil and compost for basic gardens
• Lasagna Method: Layer cardboard, straw, leaves, and compost

Sustainable Alternatives

Peat Moss vs. Coconut Coir

• Peat Moss: Excellent water retention but non-renewable resource
• Coconut Coir: Sustainable alternative, similar properties, slightly higher pH

Vermiculite vs. Perlite

• Vermiculite: Better water retention, holds nutrients, more expensive
• Perlite: Better drainage, lighter weight, less expensive

Cost-Saving Strategies

Hugelkultur Method

For deep beds (18+ inches), place logs, branches, and wood debris in the bottom third. This reduces soil needs by 30-40% and provides long-term nutrients as wood decomposes.

Bulk Buying Tips

• Order with neighbors to meet minimum delivery requirements
• Buy in spring when demand is lower
• Consider "garden blend" mixes from local suppliers
• Check with municipal composting programs

Filling Strategy

Layering for Deep Beds

1. Bottom 4-6": Drainage layer (gravel or coarse wood chips)
2. Next 6-12": Hugelkultur layer (logs, branches) or core materials
3. Top 12-18": Premium soil mix for root zone

Settling Considerations

• Fresh compost settles 15-20% in first year
• Peat moss settles 10-15% when first wetted
• Always overfill beds initially
• Top up with compost annually

Special Considerations

Rooftop and Balcony Gardens

• Weight limits: Most roofs support 15-20 lbs/sq ft
• Use lightweight mix: More perlite, less topsoil
• Drainage is critical: Include drainage layer and overflow holes
• Consider modular systems: Distribute weight evenly

Contaminated Soil Areas

• Line bed bottom with landscape fabric
• Use imported soil only
• Consider deeper beds (24+ inches)
• Test soil for heavy metals if concerned

Maintenance

Annual Top-Up

• Add 2-3 inches of compost each spring
• Mix gently into top 6 inches
• Replace mulch layer
• Test soil every 2-3 years

Signs of Soil Problems

• Poor drainage: Water pools on surface
• Compaction: Hard surface, poor root penetration
• Nutrient depletion: Pale plants, poor growth
• pH imbalance: Specific nutrient deficiencies