One big challenge for Utah gardeners is soil fertility. Utah's soil is naturally low in organic matter and high in pH, two conditions that limit vegetable production. Also, gardeners often face compacted and rocky soil, especially in new housing developments. Raised beds are touted as the end-all solution for these challenges, but without understanding the basic concepts, gardeners may create a whole new set of problems while trying to solve the first.

Adding organic matter or other amendments in proper proportions, elevating the grade, and adjusting irrigation schedules are keys to successful raised bed gardening.

The overall concept of a raised bed is to enrich the soil and allow for good drainage. When soil is well drained, salts wash through and below the plant root zone. In poorly drained soil, water evaporates from the soil surface and leaves salts behind. Eventually, salt accumulates in the root zone and limits plant growth and productivity.

Soil in Utah valleys was once the bottom of Lake Bonneville, a sea that ultimately drained and evaporated. Little rainfall dissolved the calcium carbonate and other salts left behind, creating a soil with not only high pH but remarkable buffering capacity. Add acid to Utah soil and within a few weeks the pH is back where it started. High pH limits growth and productivity in vegetable and traditional flower gardens. The most effective solution is to add organic matter to the soil. Soil particles hold and release elements and compounds for plant growth. Mineral soil enriched with organic matter can hold and release a greater variety of plant nutrients than mineral soil alone. With a better bank of nutrients, plants can grow more vigorously.

Organic matter is partly or fully decomposed or digested plant materials. Add compost, shredded leaves, sawdust, peat moss, manure, and other organic matter to help develop good soil structure. Soil with only about 5 percent organic matter is highly productive, especially when the organic matter has been added annually or more often over the past several years. Manures should be thoroughly composted before used as a soil amendment. Composting kills most weed seed and washes out most of the salt.

Recipes for soil to fill "instant garden" raised beds often produce inconsistent results, because many ingredients are highly variable.

Some manure, for example, can raise salts to toxic levels, especially for sensitive plants. Too much peat moss mixed into raised bed soil can lead to water running off the soil surface rather than soaking in, because dry peat moss actually repels water.

"Lightening" agents like vermiculite or perlite may come in larger or smaller particle sizes, depending on the source.

Variability in amendments means every gardener will need to do some trial and error before getting the mix just right: good pH, good moisture retention, low salts, and good drainage for good aeration for plant roots.

MAGGIE WOLF has a master's degree in horticulture. She can be reached at gardenutahconsult@gmail.com