Layer soil components and mix a few inches at a time.

If at all possible, use existing soil as the primary source to fill the beds. If your garden site is elevated and blessed with good quality soil, consider scraping off an appropriate amount of topsoil during site preparation and setting it aside. This procedure is recommended only for sites located on high ground. The depression created will be prone to flooding unless water can be channeled off the site.

The same scenario occurs when soil located in pathways between the beds is removed and used to fill the beds. A heavy rain will fill the lowered pathways, turning them into quagmires. Unless the water can be channeled away from the plot to a lower area, the problem will remain.

The ideal soil for your beds is a loam. Loam soils contain varying amounts of sand, silt and clay. Most gardeners prefer a sandy loam because of its favorable drainage characteristics and ease of tilth.

By design, raised beds are endowed with superior drainage characteristics. Consequently, they can utilize a broad spectrum of soil types and be effective. Clay loam soils, which are often unacceptable, can work quite nicely in raised beds if amended with sand and organic matter.

In situations where existing soil quality, quantity or site topography is inadequate, an alternative source of fill will be needed. Ask to examine any sample of fill you are considering purchasing. Spend a few dollars to have the soil tested for salt content and texture in addition to nutrient content.

For best results, consider amending the fill soil with additional materials. At the Noble Foundation Horticulture Center, good results have been obtained by using a mix consisting of equal parts (volume) of either fine sandy loam or silt loam and peat moss. Fine-textured soils such as clay loams can be amended with equal parts sand and peat moss. Avoid using sand exclusively or in combination with only peat moss. Sand, even with copious amounts of added organic matter, tends to excessively drain, making it prone to nutrient leaching.

If you are working with large numbers of beds or deep beds, the amount of peat moss recommended might be cost prohibitive. Don't worry. Simply use the amount you can justify. With continued applications of peat moss or other sources of organic matter such as compost, the tilth and water and nutrient holding capacity of the soil will be improved over time.