Quick Answer
A 4x8 raised bed at 12 inches deep needs 32 cubic feet of soil — about 1.2 cubic yards. At 18 inches deep, the volume jumps to 48 cubic feet or 1.8 cubic yards. The standard Cambridge vegetable-bed fill is a 50/50 mix of bulk Garden Soil Mix and bulk Compost, delivered for about $80 to $120. Order from the raised garden bed materials collection — bagged big-box equivalent runs $200 to $300 for the same volume.
Why Cambridge Asks This in Late May
Cambridge — Cambridgeport, North Cambridge, Inman Square, Mid-Cambridge — runs the densest raised-bed market in the region. Triple-deckers, narrow back yards, and gardener-heavy demographics drive thousands of new 4x8 raised beds every spring. Memorial Day weekend is the planting deadline. May 22 is the order deadline for delivery in time.
This Q&A covers the math homeowners actually need.
Q: How much soil does a 4x8 raised bed need?
A: 32 cubic feet at 12 inches deep, 48 cubic feet at 18 inches deep.
The math: length × width × depth = volume. - 4 ft × 8 ft × 1 ft = 32 cubic feet (1.2 cubic yards) - 4 ft × 8 ft × 1.5 ft = 48 cubic feet (1.8 cubic yards) - 4 ft × 8 ft × 2 ft = 64 cubic feet (2.4 cubic yards)
One cubic yard equals 27 cubic feet. Round up — beds settle, and you'll want top-up soil for year 2.
Q: What is the best soil mix for a 4x8 vegetable bed?
A: A 50/50 mix of bulk Garden Soil Mix and Compost.
For first-year beds where drainage is uncertain, a 40/40/20 mix of: - 40% Topsoil Loam 1/2" Screened - 40% bulk Compost - 20% coconut coir or peat moss for drainage
This combination delivers a friable, well-drained, nutrient-rich profile that supports tomatoes, peppers, cucumbers, and most home vegetables through the first season.
Q: How deep should a raised bed be?
A: Match depth to crop: - 12 inches: lettuce, herbs, spinach, radish, pepper - 18 inches: tomato, cucumber, squash, beans, peas - 24 inches: carrots, parsnips, potatoes (deep-rooted crops)
For most Cambridge homeowners with mixed-crop beds, 18 inches is the sweet spot. The Sharon vegetable garden soil mix how-to covers the procedural side of mixing the soil components.
Q: Should I fill the bottom with logs or branches?
A: Optional — saves soil cost but settles a lot. Hugelkultur (logs at the bed base) reduces soil volume needed by 25 to 40 percent and adds long-term drainage. But the logs decompose unevenly over 2 years, dropping the soil surface 6 to 8 inches. Plan to add 2 cubic feet of soil top-up per bed each spring. The Norwell garden-install contractor article covers contractor-side bed construction in depth.
Q: How much does it cost to fill a 4x8 raised bed?
A: $80 to $120 at 12 inches deep with bulk soil.
Cost breakdown for a 4x8 bed at 12 inches deep: - 0.6 cubic yards Garden Soil Mix: ~$50 - 0.6 cubic yards Compost: ~$45 - Delivery (Cambridge) included or $20-30 - Total: $95 to $125
Bagged soil at big-box stores: $200 to $300 for the same volume. Bulk wins on cost, quality, and delivery convenience.
Q: Do I need to refresh the soil every year?
A: No — top-dress with 2 inches of compost each spring.
Full soil replacement is rarely needed. Beds improve over years as compost integrates. Annual maintenance: - April: 2-inch compost top-dress - August: Quick compost top-up if beds settled below the rim - Year 5+: Consider blending in 2 cubic feet of fresh Garden Soil Mix to refresh structure
The Plymouth County garden mix review covers the bulk-vs-bagged comparison in detail.
Q: What about raised-bed weight on a roof or patio?
A: A filled 4x8 bed at 12 inches deep weighs roughly 2,400 pounds wet.
On rooftops or balconies, consult a structural engineer first — most residential decks cannot support full raised beds without reinforcement. For patio installations, distribute the weight across joists if possible.
Q: When should I order soil for a 4x8 bed in Cambridge?
A: Order by Wednesday for Friday delivery. Cambridge delivery windows are short during peak Memorial Day demand. Browse the Cambridge landscape supply collection for current scheduling.
Q: Can I plant directly after filling, or does the soil need to settle?
A: Plant the same day or next day. Bulk soil mixes are workable on delivery. Water the bed deeply once after filling — this settles the soil 1 to 2 inches. Top up if needed before planting. The Newton Memorial Day demand update covers the broader regional supply picture.
The Cambridge 4x8 Raised-Bed Playbook
- Order soil by Wednesday for Friday delivery.
- Build or refresh the bed Friday or Saturday morning.
- Fill with 50/50 Garden Soil Mix + Compost to within 2 inches of the rim.
- Water deeply once to settle.
- Plant Memorial Day weekend.
- Mulch around plants with 2 inches of straw or shredded leaves.
This same window reads as a season-close in 2026 — see May 1: Closing Out Spring Mulch Season Across Plymouth County for the year-later retrospective.
For Cambridge-specific vegetable timing and disease pressure, the UMass Extension Vegetable Program is the regional authority.
