There are over 300 different species of Delphiniums available to plant in the garden. This tall plant features large, cup or spur-shaped flowers covering a long spike.
Delphinium care is fairly straightforward and rewards gardeners with showy towers of blooms for their efforts.
Types of Delphiniums
Most of today’s popular cultivars of Delphiniums are a cross between D. elatum and D. grandiflora. Here are a few of those varieties:
- Magic Fountain: The Magic Fountain Delphinium grows between 2.5 to 3 feet tall. Blooms can be white, white with dark centers, blue, or pink.
- Centurion: This variety features semi-double blooms of white, purple, or blue. The plant grows to approximately 3 feet tall.
- Summer Nights: A hybrid from D. grandiflorium, this is a dwarf variety that stays at a height of between 10 to 12 inches with midnight blue flowers.
- Pacific Giant: Typically grown from seed, the result is often bloom combinations of varying colors. The plant will grow to six feet tall.
When to Plant Delphinium
Spring and early fall are the best times to plant Delphiniums as this allows time for the roots to establish but not have to struggle through the hottest part of the summer. If you choose to start your Delphiniums from seed start plants indoors 10 weeks prior to your location’s last frost date.
Selecting a Planting Site
When choosing a spot to plant your Delphiniums, pick a spot with full sun exposure. Shelter from strong winds is also very important as Delphiniums are prone to breakage due to their heavy tops and hollow stems.
The soil needs to be fertile and well draining. Increase the nutrient levels in poor soil by using a shovel or garden fork to loosen the top 10 to 12 inches of soil. Next, spread a 2 to 3-inch layer of compost or aged manure over the site and work it into the soil. For heavy, clay-based soils, improve drainage further by adding peat moss to the soil and working that in as well.
Delphiniums prefer soil that is slightly alkaline. To measure the pH level of your soil use a soil test kit. Aim for a pH level of between 6 and 7.5. To increase the alkalinity of your soil add lime or wood ash to the soil and work that in before testing again.
Delphinium: How to Plant
To plant your Delphiniums, dig a hole twice as wide as your plant’s current container
and as deep as the container is tall. Remove the plant from its container and gently squeeze the root ball a few times to loosen the soil and spread out the roots. Place the plant in the middle of the hole and spread out the roots as much as possible. Backfill the hole with soil until the top of the root ball is level with the soil’s surface.
Water your Delphiniums until the soil is saturated but not soggy. Lastly, lay a 2 to 3-inch thick layer of mulch around the base of the plant, leaving 2 inches between the plant’s stalks and the mulch.
Companion Plants for Delphiniums
There are several reasons why companion plants are beneficial including aesthetics, protection, and improved growth. Delphiniums benefit from support to protect the plants against breakage. The support can be in the form of other tall plants or with garden stakes.
Tall Plants for Support
These sun-loving plants are quite sturdy and offer great support for the more delicate Delphiniums. Sunflowers varieties will grow as short as 1.5 feet or up to 12 feet tall, providing as much protection as you need for your plants.
Hollyhocks bloom from early summer to fall. These plants prefer the same amount of sunlight as well as soil and moisture conditions. Growing to a height of around 9 feet, Hollyhocks are self-seeding so they’ll renew themselves year after year.
Tall Ornamental Grasses:
There are several varieties with interesting colors and patterns to add visual interest. Grasses can be planted in thick clumps to lend sturdy support right where it’s needed.
If you decide to use stakes to support your Delphiniums, hide the stakes with these medium-height plants.
Medium-Sized Companion Plants
Echinacea: Also known as the Coneflower, these plants grow up to 5 feet tall but remain sturdy. The bright-pink flowers add visual interest when mixed with the Delphinium spikes.
Phlox: Blooming from mid to late summer, Phlox grows to a height of between 3 to 4 feet. To ensure the most sturdy stalks, prune away any weak stalks once they reach 6 inches tall until only five or six strong stalks remain.
Lilies: Lilies come in a wide variety of colors and grow between 2 and 6 feet tall. The plant’s strong stalks and multiple leaves help hide any garden stakes.
Plant Chamomile or legumes along with your Delphiniums to give both plants nutrient benefits.
To get the most from your Delphiniums all growing season, proper watering and feeding is essential. Water your Delphiniums regularly, especially in hot weather. Water until the soil is saturated but not soggy as this leads to crown rot. Avoid spraying water on the foliage as this contributes to leaf fungus issues.
Delphiniums bloom better when they are given a boost of nutrients via a balanced fertilizer. The first feeding should occur immediately after planting to get your Delphiniums off to a good start. Give the second feeding mid-season to encourage a second round of blooms. If you notice your Delphinium’s foliage turning yellow that is a signal to fertilize.
Remove mature flower spikes to redirect the plant’s energy to the developing the side shoots. Use sharp and sterile shears to snip the stems where it branches off of the main stalk. When all the first round of flowering is done, cut back the plant to leave 2 inches of stalk above the soil to encourage a second blooming in late summer.
Overwintering Your Delphiniums
Once all blooming for the season is done, cut the stalks back a final time to 2 inches above the soil’s surface. Lay a thick layer of mulch over the snipped stalks to protect them from frost damage.
Delphiniums are tall, showy flowers that are an asset to any garden design. The plant’s height makes it a great focal point, just ensure there is some form of support to avoid wind damage. Your reward is beautiful, fragrant blooms that look great outdoors or as cut flowers in your own floral arrangement.
Growing Delphiniums FAQ
On average, Delphiniums last between three and five years.
Yes, Delphiniums are toxic and should be kept away from pets and small children.
Yes, Delphiniums are also known as Larkspur, a name given to the flower by the English who thought the flower looked like the claw of a Lark.
Delphiniums bloom from last spring to early summer.
Keep cut Delphiniums looking great by placing the vase in a cool spot in your home out of direct sunlight.