Selecting flowers for alkaline soil can be a challenge when you realize how many acid-loving flowers are available and how few flowers thrive in an alkaline pH level. Fortunately, there are enough flowers for alkaline soil to choose from to create an ideal flower garden in pH levels over 7.
Sweet pea flowers (Lathyrus odoratus) are a cool-season annual plant that prefers neutral to slightly alkaline soil with a pH level of 7.0 to 7.5. Sweet peas bloom in the springtime in a variety of colors including pinks, reds, purples and whites. It thrives in full sun and prefers cool, moist, well-drained soil rich in humus, according to the Washington State University Clark County Extension.
Common lilac (Syringa vulgaris) is a flowering shrub for alkaline soil. Common lilac displays fragrant flowers during late spring in varieties of the following colors: purple, white, pink, lavender and blue. According to the University of Illinois Extension, this flower thrives in full sun and prefers moist, well-drained soil.
Delphiniums (Delphinium spp.) are a perennial flowering plant that prefers alkaline soil; the pH should be neutral to slightly alkaline, according to the Iowa State University Extension. Delphiniums display single or double blooms in blue (most common), red, pink, white, violet and yellow. These flowers thrive in full sun with moist, well-drained soils.
Clematis (Clematis spp.) is a woody, climbing, flowering vine that is a member of the buttercup family. The clematis plant prefers alkaline soil but tolerates neutral to slightly alkaline soil with a pH level of 7.0 to 7.5. With more than 300 species, clematis plants display a wide array of flower colors including blues, pinks, purples, and yellows. They thrive in full sunlight (while roots hide in the shade) and cool, moist, well-drained soil, according to the University of Illinois Extension.