Many gardeners love an ever-changing garden filled with colorful annual flowers. But soil acidity can have a dramatic effect on the success of any garden, especially one built around annual blossoms. Soils with a pH level of 1 to 7 on a 14-point scale are considered acidic. Although many flowers do well in slightly acidic soils, selecting annual flowers for soil that is more acidic can be a challenge.
Soils are graded on a pH scale of 1 to 14, with numbers 1 through 7.0 considered acidic, and 7.1 through 14 alkaline. Acidic soil is often challenging because it can interfere with the way the plant takes up nutrients. Determine what kind of soil you have before you plan your garden, so you can match plants to particular soil types. You can also adjust the relative acidity of your soil using amendments.
Determining Your Soil Type
A good way to match your plantings to your soil is to get a soil test kit, often available from cooperative extension services operated by colleges and universities or from commercial garden supply stores. The kits contain instructions, soil collection tools and a mailing pouch to send in your sample. Your results will be mailed to you or sometimes can be obtained online. The result report often provides extra information such as fertility and nutrient levels.
Annual flowers typically live out their growing cycle in one year. Since annuals are replanted every year, some gardeners find them especially useful in giving their gardens a new look every summer. Some annuals, like annual vinca (Catharanthus roseus) or French marigold (Tagetes patula), do reasonably well in slightly acidic soil -- roughly between 6.0 and 7.0 on the pH scale. If you have even more acidic soils try nasturtiums (Tropaedum majus) and the popular butterfly flower (Schizanthus).
Ivy Leaf Geranium
An attractive annual flower for acidic soils is the ivy leaf geranium (Pelargonium peltatum). Often chosen for window boxes in Europe, the geranium adapts to container culture or bedding plant arrangements. Doing well in soils with a pH below 6.0, the geranium's growth suffers when acidity reaches about 5.5. Addition of lime can bring acidity levels into a more tolerable range for ivy leaf geraniums.
Place your geraniums in a wind-protected spot where they'll get full sun for six to eight hours a day and you'll enjoy colorful and healthy blooms all summer.