Delphinium Bushes

Characteristics

• Delphinium bushes can reach a height of 4 to 6 feet when mature and in bloom, although several cultivars are shorter. The plant grows as a mound of dark green, glossy leaves that sends up tall flower stalks in summer, generally from June through July. Each spike is covered in colorful, 3-inch-wide flowers that may be single or double. The flowers open in sequence, beginning at the spike's lower end, so each stalk is in bloom for one or two weeks. Flower colors vary, but some delphiniums produce blooms that are a true, deep blue, a rarity among plants.

Site Selection

• A delphinium does best in a spot that gets full sun for most of the day. It can tolerate some light shade, especially during afternoon hours in areas with strong, hot sun, but too much shade can lessen flower production. Because the flower spikes can be quite tall, the plant is not a good choice for a location subject to strong winds. A delphinium is best planted in early spring, to give it a full season to develop. It can spread to cover an area of 2 to 3 feet after a few years, so if you're planting several specimens, space them several feet apart to give them room to spread without crowding.

Soil and Water

• A delphinium does best in fertile, loamy, well-drained soil. Adding compost or composted manure to your soil at planting can help increase its fertility. If your soil contains clay and tends to hold water, you can also add some fine sand to improve its drainage. This plant needs regular watering, does best with about 1 inch of water each week and should be given supplemental water during dry spells. Adding a 2- to 3-inch layer of organic mulch in spring can help conserve soil moisture, while also suppressing weeds.

Other Care

• As delphinium flowers fade, removing old flower stems can stimulate a second bloom later in the summer. Taller varieties of delphiniums need a strong stake to help support their blossom spikes. Examples of these tall types include cultivars called "Pacific Hybrids" or the "Blackmore" strains, which can be up to 6 feet tall. A delphinium is susceptible to certain fungal diseases, including powdery mildew, blight and leaf spot. The best preventive for these problems is following good cultural practices. These include growing the plant in an area with good air circulation, clearing debris from beneath it regularly and watering with a soaker hose or drip irrigation, keeping its leaves as dry as possible.