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How to Grow: Delphinium
Bloom Period and Seasonal Color
Early to mid summer in colors such as blue, pink, white, rose, and purple
Mature Height x Spread
2 to 6 feet x 1 to 2 feet
attracts beneficials, deer resistant
There is no more stately a flower than the delphinium. This English garden standard has spiky flower stalks that can reach 6 feet tall depending on the variety. They are breath taking when grown in clumps. The flowers are single or double with contrasting colored centers or “bees”. The flowers surround the stalk so the delphiniums look like majestic, colorful pillars in the back of the flower border. They’re not without their nuances though. The spikes need support and the plants can be finicky about lasting more than 3 to 4 years in the garden. The blooms can be used in cut flower arranging and bees, butterflies and beneficial insects appreciate the tall blooms.
Where, When and How to Plant
Delphiniums are hardy throughout New England. They’re difficult to grow from seed so it’s best to buy plants locally from garden centers in the spring to plant from spring to summer. Delphiniums like a slightly alkaline soil, so add lime to raise the pH above 6.5. They need well-drained, moist, compost-amended soil, to grow best. Plant delphiniums in full sun on the south side of a house or garage protected from strong winds. Space plants 2 to 3 feet apart.
Keep plant well watered. Mulch around the base of plants to keep weeds away and the soil consistently moist. Fertilize monthly with an organic plant food.
Regional Advice and Care
Tall varieties of delphiniums need support. Place stakes or plant rings around developing flower stalks when they are 1 foot tall to protect them breaking due to summer thunderstorms. There’s nothing worse than having your fully opened delphinium stalk snap in half due in a windstorm. Delphiniums are magnificent when blooming, but shabby when finished flowering. Remove the spent flower stalks soon after blooming and secondary stalks often form giving you more flowers in late summer. Plant away from eaves of the house where rain dropping off the roof can damage the blossoms.
Companion Planting and Design
While tall delphiniums grow well in the back of a border or against a house, shorter varieties look good in the front of your garden. Pair tall delphiniums with iris and phlox and lower growing varieties with alyssum and ageratum. Plant them in a cutting garden. Cut flower stalks when they’re three quarters open for best blooms.
“Pacific Giants Mix” is a standard group of varieties with blue, violet and rose colored double flowers. “Blue Springs” only grows 2 feet tall with blue flowers. The “Magic Fountain Series” has a mix of white and blue flowers that grow 3 feet tall and are good for cutting. “Magic Fountain Sky Blue” is a particularly beautiful selection. The “New Millennium Series” from New Zealand have large flowers on strong stems but the plants are longer lived.
Excerpted from my book, New England Getting Started Garden Guide.