Your delphiniums will perform best if you stake them right before they begin to bloom.
Perennial delphiniums bloom from late spring to early summer, and may even grace you with a second showing in later summer or early fall. To make the most of the blooming season, deadhead these plants regularly. Deadheading, or the removal of spent flowers, is simply a way of coaxing these plants to form new blooms on the offshoots of their main stalks. When you remove the flowers before seeds are allowed to mature, delphinium plants sense that the seeds need to be replaced and send up more blooms. You're essentially fooling them into making more flowers for you.
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Cut stately blooming delphinium spikes freely for your stunning indoor arrangements throughout the growing season. Use clean, sharp shears and make your cuts just below the lowest flower on the stem.
Deadhead your delphiniums as the individual blooms fade. Cut a spent flower's stem completely back to the nearest pair of leaves or set of branching stems. This is where the next flower buds will emerge.
Remove the blooming stalk as soon as its last remaining flower is spent. Cut the spike off cleanly at the base of the plant.
Prune any dead or damaged leaves out of the plant to tidy it up, if you wish. Don't remove any more of the foliage than necessary. Your delphinium will form new shoots from its base soon after you've cut the flower stem. The new growth will develop into flower spikes later in the season and they'll need the nourishment that the leaves provide.