Annual Flowers: Site Selection

The key to growing garden flowers successfully is to match the planting site with the needs of each specific flower. Before selecting plants, analyze the site. A plant that needs good soil drainage will not perform well in a site that drains slowly. Before selecting plants for any site, consider the amount of sunlight, microclimate temperature, competition from tree roots, and soil drainage and aeration.

Sunlight - Plants vary in the amount of sunlight they require for optimum growth. Too little sunlight can lead to reduced flowering and leggy plants. Too much sunlight can burn or fade the foliage of shade-loving plants. Light, temperature, and water are closely interrelated. Plants listed as preferring partial shade may tolerate more sunlight if temperatures are moderate and adequate water is provided.

When evaluating light exposure, note the duration and intensity of sunlight the site receives. Four hours of full sun during the morning is very different from four hours of stronger, more intense afternoon sun. There are also many types of shade, and the amount of light in shaded locations will vary with the type, number, and size of trees in the area. If the site receives more than three hours of unfiltered midday sun, it should be treated as a “full sun” site. “Partial shade” can be defined as receiving unfiltered morning sun, but shade during the afternoon hours, or moderate shading throughout the entire day. A “heavily shaded” site would receive very little direct midday light and less than 60 percent of the sun’s intensity during the remainder of the day. Few flowering plants do well in deep shade. Introducing more light to a shaded location can greatly increase flower production. Removing some tree limbs can allow more light to reach the ground below.

Temperature - Very few flowers look attractive and flower profusely from early spring through late fall. Cool-season flowers such as dianthus, pansies, and snapdragons grow best when the temperatures are mild; they slow or stop flowering when exposed to high summer temperatures. It is possible to extend the flowering season of cool-season annuals by placing them in a protected location, shaded from direct sunlight from about noon to 4:00 p.m. Plants adjacent to a paved surface or brick wall will experience warmer temperatures and their flowering period will be shortened. Heat-loving flowers such as gaillardia, portulaca, verbena, and vinca do not begin to flower until early summer, and they should be planted in high-temperature situations. Planting them on the north side of the house in light shade will delay and reduce their flower production.

Soil moisture - Examine the interrelated factors of drainage, moisture retention, and soil aeration of the site (refer to Chapter Three). Frequent heavy rains in combination with poorly drained soils will cause excessive soil moisture and limited air space in the soil, thus reducing plant growth and increasing the chances of root rot problems. One way to check for adequate drainage is to dig a hole 10 inches deep and fill it with water. After it drains, refill it with water. If the water drains in 8 to 10 hours, the site is adequately drained for most flowers. Subsoil compaction or the presence of a hard pan beneath the bed can affect water drainage and soil aeration. It may be necessary to deep till beds to break up the subsoil and increase the drainage rate.

The amount of air in the soil depends on the type of soil, soil compaction, and how quickly water drains from the soil. Clay soils normally have poor drainage and aeration, but excellent water retention. Water does not always enter clay soil easily; it often puddles on the surface rather than soaking in. Sandy soils have good drainage and aeration, but retain little water. The addition of organic matter such as pine bark or composted yard waste will enhance soil aeration, water movement into the soil, and drainage of clay soils. It will also improve water retention in sandy soils.

Prepared by: Erv Evans, Consumer Horticulturist