Blue flowers are a special delight in the garden, in part because they are not common. Some of the flowers promoted as blue are actually purple. But there are a few dependable, true-blue favorites, as well as more exotic choices. Pair blue flowers with white for a soothing look, or combine with bright reds, orange or yellow to make a bolder statement.
Hydrangeas: Whether Blue or Pink Depends on Soil
For at least one type of flower, whether they turn out blue or not depends on the condition of the soil. Hydrangeas, a broad-leafed deciduous shrub that grows to be 4 feet to 12 feet high, have large round blossoms. With some varieties, the blossoms are white, while others will be pink or blue depending on the soil. Blue hydrangeas require aluminum, which is only present in acid soils. If grown in alkaline soils, the plant will have pink blossoms. The soil can be altered to make it more acidic if you want blue flowers: just apply aluminum sulfate or sulfur in the spring to reduce the pH to between 5 and 5.5. If you don't know whether your soil is acid or alkaline, you can purchase a testing kit from your local nursery or extension service.
Early Spring: Scilla and Bluebells
Scilla, or Siberian squill, appear in early spring and bloom for no more than two weeks. They have bright blue flowers growing on 6-inch stems with dark green foliage. Their flowers are up to an inch wide. Scilla grows best in partially shady areas. Scilla, a perennial, is grown from a bulb and tends to spread.
Virginia bluebells, or Mertensia virginica, grow in shady areas of the garden; they are also native to the woodlands. The plant's trumpet-shaped flowers grow from a coiled stalk; they reach a height of 1 foot to 2 feet. Virginia bluebells bloom in early to mid-spring. They needs lots of water in order to thrive.
Early Summer: Lobelia
Lobelia, or Lobelia erinus, is a plant with trailing stems well-suited to hanging baskets. Lobelia produces bright blue flowers from early summer until the first frost. This plant is an annual that grows to be 3 inches to 10 inches long. The flowers will die during the hottest part of summer but come back when it cools off. They require a lot of water and fertilizer.
Midsummer to Fall: Morning Glories
Morning glories, or Ipomoea tricolor, are an annual that can climb 10 feet to 15 feet up a fence or trellis. Blue morning glories have large blossoms and big heart-shaped leaves. A smaller variety, Convolvulus tricolor, grows 12 inches to 18 inches tall and comes in light blue, as well as pink or white. Morning glories bloom from mid-summer until frost. They require a lot of water but thrive in poor soil and don't need much fertilizing.
Unusual Blue Flowers
Agapanthus, also known as Lily of the Nile, hales from South Africa, but with a little care, it can thrive in cooler locations. Agapanthus has clusters of blue flowers that bloom from early to mid-summer. The plant has dark green glossy leaves and grows from 1 foot to 4 feet tall, depending on the variety.
Another unusual blue flower is sea holly, or Eryngium amethystinum. The flower's silvery leaves contrast nicely with its blue blossoms, which appear in midsummer. This plant requires lots of sun but little moisture.