Larkspur (Delphinium) grows as a perennial with a limited lifespan of only two to three years unless ideal growing conditions exist. The plant grows from 1 to 7 feet in height. During the late spring and early summer, long flower spikes appear in shades of blue, lavender, yellow, pink and white. The plant, native to Siberia, offers exceptionally winter hardiness down to U.S. Department of Agriculture zone 2, according to the University of Maryland.
The larkspur enjoys full sunlight with moist soil. Ample root systems grow when the larkspur is planted in well-drained soil with abundant organic material. Adding a few inches of mulch to the top layer of the soil helps keep the plants roots moist during the heat of summer. The plant prefers a slightly alkaline soil pH.
The larkspur benefits from being planted in an area that offers wind protection because it is easily blown over. Large flower spikes often require staking to hold them.
Moist soil conditions help insure a healthy root system in the larkspur plant. The plant does not tolerate periods of drought and will show wilting or death of its foliage and blossoms if allowed to dry out for a few days. The larkspur benefits form drip irrigation or a soaker hose so the plants flowers do not become wet. Wet flower heads often bend or break with the weight.
A heavy feeder, the larkspur requires abundant nutrients to thrive. The plant benefits greatly from regularly fertilizing. In the spring, an application of organic or general-purpose fertilizer helps the larkspur develop its ample foliage and flower buds. After flowering, another application of fertilizer helps the plant develop seeds and prepare for the winter.
The larkspur spreads and grows easily from seeds. To control the plants, spread in the flower bed, prompt removal of dying flower heads is suggested to limit seed production. Propagation is also attained from basal cutting and fall rhizome division.
Larkspur is categorized as extremely toxic according to North Carolina University. All parts of the plant are poisonous. It contains alkaloids delphinium and ajacine. The plant causes burning of the mouth and throat if ingested, along with convulsions, muscle spasms and paralysis of the respiratory system. Death follows if untreated.