Not many plants will look good, grow actively and flower heavily from spring to fall. Some like it cool and some like it warm. Seasonal variation in temperature will limit their usefulness as well as where they are placed in the garden. Cool season flowers such as dianthus, snapdragon, pansies, Virginia bluebells, and primrose prefer the spring and fall or a spot where they can be protected and shaded from direct sun from about noon to 4 p.m. Planting in protected locations helps to extend the useful bloom time for these plants.
Heat-loving plants such as melampodium, portulaca, yarrow, sedum and verbena like it warm and dry for best performance. Heat tolerance is a very valuable characteristic for plants being grown in midwestern gardens.
Light and temperature are closely related. Plants that prefer lower light may tolerate more sun if the temperatures are cooler and if moisture is in good supply. When evaluating light exposure, note how much and at what intensity of light the site receives. Four hours of full sun in the morning are cooler than four hours of full sun in the afternoon. In a shaded location, the degree of light getting to the plants can vary. In general, if a site receives more than three hours of unfiltered mid-day sun, it is probably best treated as a full-sun site and plants should be selected accordingly.
Partial sun can be thought of as a site that gets unfiltered morning sun but shaded during the afternoon hours or "dappled" shade throughout the day. Areas in deep shade receive very little direct mid-day light and less than 60 percent of the sun's intensity during the remainder of the day. Mismatching plant light preferences with actual light conditions can lead to a reduction in flowering, tall, leggy growth, stunting of plants, or leaf scorching.
Water stress can go from areas that remain wet and damp to areas that are drought prone — even in the same landscape and often in close proximity to one another. Bed preparation is essential for avoiding moisture excess or drought conditions.
For most situations, some watering may be needed at some point during the growing season. For sites where soils are dry or where irrigation is going to be minimal, choose plants that are drought-tolerant. Keep in mind that even drought-tolerant plants will need a period of establishment with sufficient water to get them deeply rooted in the soil, so they can successfully handle drier conditions. The best insurance against excessive moisture is proper bed preparation coupled with either drain tile or the construction of raised beds.
Plant choices can be made based upon the plant’s ability to tolerate wet soils or even flooded conditions.
A majority of overwatering problems, assuming a well prepared site, occurs from too frequent irrigations rather than from too much water applied at any one time.
Shaded dry soil creates a difficult site for plants to grow in. It is especially important to understand that dry shade, such as under a heavy tree canopy, imposes a number of stresses that only a select group of plants can adapt to. Plant selection is important when working with these conditions. Keep in mind that plants for dry shade will be successful if given proper conditions to get well established.
Plants depend on the soil for support, moisture and nutrients. Heavy rains or frequent irrigation in combination with poorly drained beds reduces plant performance and increases the chance for loss due to root disease. On the other hand, beds that have excellent drainage may have little water holding capacity and require frequent watering to maintain plants. Improving the water holding capacity coupled with drought tolerant plants make gardening in these sites more enjoyable. Adding soil amendments such as compost aids in improving soil structure and the critical balance between water and air in the soil. Both are all important elements for good root growth, which leads to successful plant growth. No one thing is more important in reducing stress to plants than proper bed preparation prior to planting.
When looking for plants to fit the conditions of a particular site, there are many choices. When moving away from impatiens and petunias, some of the choices may not be familiar. Here are a few to consider. There are many more. These examples include plants suitable for dry to moist shade and for sunny dry conditions to sunny average soil moisture conditions.