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Buying Topsoil - What to Know Before You Buy
Be aware that there are no legal marketing standards for topsoil. "Topsoil" simply refers to the uppermost layer of soil and not all topsoils are suitable for your garden. Below are some key points for you to consider when buying topsoil for your garden.
Rocks and Debris: If you can, take a look at the soil before you buy it. Screened topsoil should have no trash, debris, or rock fragments greater than 3 inches in diameter (it may have up to 5% by volume of smaller rocks). Buying unscreen topsoil will be cheaper, but the few dollars saved per cubic yard is not worth the time you'll spend removing rocks and debris from your new topsoil.
Texture: You generally want to buy some type of loam (e.g., sandy loam, humus loam, silty loam). Don't buy fill dirt or simple topsoil for your garden. If you come across "manufactured topsoil," be careful - this may be ok, but is usually some sort of coarse mineral (sandy) base with organic matter added. Not all are useful in the garden.
Organic Matter: Garden topsoil should contain between 2% and 10% organic matter. Organic matter allows the soil to hold water and nutrients, and to drain freely, but too much organic matter can cause the topsoil to compact. Ask the topsoil vendor for the approximate percentage of organic matter in their topsoil.
Color: Don't be fooled into thinking that darker topsoil is better. Sometimes darkness is associated with increased organic matter (which is good), but it can also mean that the topsoil has been dredged from wetland areas (which is bad - it's often very acidic, poorly structured, and may not do well when placed in your garden). Always ask where topsoil came from before buying it.
Amendments: You will probably have to add lime and fertilizer to your new topsoil, and perhaps organic matter (e.g., screened compost, composted manure, leaf-mold).
Amount: You'll generally want about 4" of topsoil coverage in your garden. If you're building raised beds, you could need up to 10" or more in depth. Carefully measure the area where the topsoil will go and use this handy topsoil, compost, and mulch marterial calculator from Snow's Farm to determine how much material you need.
Price: Topsoil is generally sold by the cubic yard. Prices vary depending on location, but typically range from $15 to $20 per yard “picked up” and from $17 to $25 per yard “delivered.” The minimum amount commonly delivered is from 3 to 6 yards.
Soil Testing: It's unlikely that the topsoil vendor will have tested the soil. Before planting, you should have a soil test to check for lime and fertilizer requirements and to assess its texture. If you plan to grow vegetables in the new topsoil, you may also want to test for heavy metals, such as lead.