Potting Soil Vs. Topsoil for Annuals

Overview

Regardless of your location across North America, annual flowers often grow easily from seeds or as small seedlings bought ready for planting into the garden. When there is no danger of a killing frost, plant annual flowers (or vegetables) where they will receive appropriate sunlight levels as well as a moist, nutritious soil. Always match the annual flower plant with the right kind of soil--not all plants prosper in moist soil, some like dry soil.

Topsoil Quality

Not all garden soils are created equally. Use crumbly, organic-rich loam for growing annuals. Sandy soil is fast-draining, lacks nutrition, dries out and heats up quickly. Clay soils are heavy and crust over as they dry, according to the University of Missouri Extension. Examine your garden's soil and amend it with organic matter like compost or well-cured manure. Till the soil to a depth of 8 to 12-inches, deeply incorporating organic matter.

Potting Soil Features

Potting soil or "mix" is rarely a true soil, as it contains peat, coir, perlite, sand or vermiculite particles to create a fine-textured, porous medium that remains moist. It's often called a "soilless" mix or medium. In comparison to your native or pre-existing garden top soils,buying large quantities of formulated potting soil is expensive. Potting soil is specially formulated for use in various sizes and plant uses of containers.

Benefits

Topsoil is a growing medium for annual flowers as long as it is fertile, rich in nutrients and organic matter, retains moisture but also allows for drainage of rainwater. You can directly sow seeds of annual flowers in the garden topsoil, or transplant nursery seedlings. Use potting mix when sowing seeds or growing plants in any container. The loose, soilless aspect of potting mix won't crust over, compact or harden.

Shortcomings

There is generally little nutrition in potting soil, according to Cornell University Cooperative Extension. Potting soils' formulation facilitates the support of plant roots, proper aeration and water drainage. Addition of organic matter or manmade granular or liquid fertilizers is needed for healthy plants. Topsoil has a tendency to compact or crust over when it alternates between wet and dry. When seedlings are germinating, a crusty soil surface limits seedling growth. Never use topsoil in a container as it's too dense and limits aeration and drainage. It also tends to become rock hard after only a few waterings as it settles and dries.

Recommendations

When growing annuals, use the appropriate soil type based on your growing environment. Grow annuals in a fertile topsoil in the garden. Amend the soil with organic matter and till it deeply to create the best growing conditions. If you opt to grow annuals in containers, from hanging baskets to large patio pots, rely on potting soil. Add fertilizers to topsoil or potting soil to regulate the growth and flowering as needed across the growing season.

Keywords: growing annuals, annual flower soil, potting soil characteristics, garden topsoil

About this Author

James Burghardt became a full-time writer in 2008 with articles appearing on Web sites like eHow and GardenGuides. He's gardened and worked professionally at gardens in Colorado, Florida, Minnesota, New York, North Carolina and Pennsylvania. He holds a graduate diploma in environmental horticulture from the University of Melbourne, Australia and a Master of Science in public horticulture from the University of Delaware.