Calculate exactly how much soil or compost you need for your garden
Underestimating soil is the single most common mistake first-time raised bed builders make. A standard 4x8x12-inch raised bed needs 32 cubic feet of soil — far more than most people expect. At a typical garden centre price of $7–$9 per 2 cubic foot bag, that's 16 bags and roughly $120–$145 just for soil. Knowing your numbers before you go shopping saves time, money, and frustration.
For Canadian gardeners, quality soil is especially important. Our native soils vary enormously — heavy clay in much of Ontario and the Prairies, rocky shallow soil in BC and the Shield, sandy soil in coastal regions. Raised beds let you bypass whatever you're working with and create an ideal growing environment from scratch. Don't cut corners on soil quality — it's the foundation everything else builds on.
A 4x8 foot raised bed at 12 inches deep needs 32 cubic feet of soil — about 16 bags of bagged soil (2 cu ft each) or roughly 1.2 cubic yards of bulk soil. At 6 inches deep you need 16 cubic feet (8 bags). At 18 inches deep you need 48 cubic feet (24 bags). Always add about 10% extra to account for settling — soil compresses over time, especially after watering. Enter your exact dimensions above to get a precise number for your specific bed.
The classic "Mel's Mix" from Square Foot Gardening is one-third compost, one-third peat moss (or coco coir), and one-third coarse vermiculite. This creates light, moisture-retentive, nutrient-rich soil that drains well and never compacts. A more budget-friendly option is 60% quality topsoil, 30% compost, and 10% peat moss or coco coir. Never use straight garden soil or topsoil alone in a raised bed — it compacts badly, drains poorly, and will stunt plant growth.
For anything over 1.5–2 cubic yards, bulk soil ordered from a local landscape supplier is significantly cheaper than bagged — often 50–70% less per cubic yard. A cubic yard of quality triple mix (topsoil, compost, peat) from a landscape supplier in Canada typically costs $50–$80 delivered versus the equivalent in bags at $180–$220. The tradeoff is that bulk requires a driveway, wheelbarrow, and physical work to move. For a single 4x8 bed, bagged soil is convenient; for multiple beds or a large garden, bulk is the clear winner financially.
Most vegetables grow well in 12 inches of soil depth. Shallow-rooted crops like lettuce, herbs, and radishes can manage in 6–8 inches. Deep-rooted crops like carrots, parsnips, and potatoes prefer 18–24 inches for best results. Tomatoes and peppers do best with at least 12 inches. For a versatile bed that grows almost anything, 12 inches is the practical standard and the most popular raised bed height. If you're building over hardscape like concrete or gravel, 18 inches provides extra buffer for root development.
Yes — this is one of the most important things you can do for a productive raised bed. Soil loses volume and nutrients each season as plants use them and organic matter breaks down. Adding a 1–2 inch layer of finished compost each spring replenishes nutrients, improves soil structure, and feeds the soil microbes that make nutrients available to plants. Over several years this annual top-dressing builds increasingly rich, productive soil. Use our Composting Calculator to see how much compost your household can produce each year.
Hugelkultur (pronounced hoo-gul-culture) is a technique where you fill the bottom half of a raised bed with logs, branches, and woody debris before topping with soil. As the wood breaks down over years, it retains moisture and slowly releases nutrients — and significantly reduces how much purchased soil you need upfront. It's particularly popular in Canadian prairie gardens where water conservation matters and free wood material is abundant. The tradeoff is that the bed surface will sink as wood decomposes, so plan to top up with compost annually.
Learn how to prepare and use soil for the best results.