By Dennis Hinkamp, Utah State University Extension 
Annuals are the tempting quick fix to garden beauty, and they are for sale at every supermarket, hardware store, and unpaved patch of ground right now.
Why do some annuals thrive and grow, regardless of the soil type and conditions, while others wilt and die at the drop of a credit card?
Several factors influence their growth and blooming habits, explains Jerry Goodspeed, Utah State University Extension horticulturist.
“The first step is to start with healthy plants,” he says. “Purchase annuals with dark green foliage and roots that just fill the pony-pack soil. Although it is tempting to purchase annuals in full bloom, this is not always the best idea. Often, annuals that are not yet in bloom establish faster and look better two weeks later.”
Avoid root-bound or leggy plants, he adds. Any discoloration of the foliage normally indicates a nutrient problem and should be shunned. Steer clear of plants that look stressed. Symptoms include plants that are wilted, lack thick foliage, are yellowing, or are water-logged.
“Once home, annuals need to be acclimated to the weather for a couple of days before planting,” Goodspeed says. “Spending their whole life in a greenhouse does not prepare them for the shock of being placed outdoors in full sun. Allow a few days for them to adjust. Leave them out one day for four hours, six the next day and then eight. This prepares annuals for their new growing environment.”
Prepare good soil for annuals before planting, he suggests. Amend the soil with organic matter. This improves the tilth and structure of the soil. Till the soil as deeply as possible to allow the new roots plenty of room to grow.
“Annual plants spend their early life growing roots in a small pony pack,” Goodspeed says. “Once planted in the flower bed, many of these plants are not smart enough to realize they can stretch their roots out into a larger area. Most roots need to be motivated to grow and extend in the surrounding soil. This can be accomplished by either removing the lower part of the root ball or scoring it just before planting. Although it may seem cruel to damage the young root system, it does tend to encourage new root growth.”
Plants that are leggy or have excessive blossoms benefit from a light pruning after planting, he says. Although this eliminates some of the flowers at the time, it encourages bushier, fuller foliage that eventually produces more blossoms and fills in faster.
After planting annuals, be sure to water them thoroughly, he adds. Do not overwater or let them sit in a puddle. Let the top 2 inches of soil dry between watering. This helps the plants develop a deeper, healthier root system. Fertilize with a water soluble fertilizer about two weeks after planting the annuals.
Regularly check annuals for signs of insect or disease damage, Goodspeed says. Most problems, if caught early, are more easily controlled before there is too much damage. The most frequent problem is overwatering. Too much water promotes root rot, white mold and other problems. Water deeply and infrequently.
Another helpful hint to beautify annual flower beds is rotating and using different types of annuals in a bed from year to year, Goodspeed suggests. Planting the same flowers in the same area year after year increases disease problems and can cause a slow decline in blossoms. Using different annuals reduces the likelihood of diseases and brings variety and interest to the landscape.