Planting, Growing, and Caring for Delphiniums
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Delightful delphiniums! The stalwart of many summer flower gardens, these showy perennials are grown for their long, colorful spikes in blue and other gorgeous hues. Flowering all summer, delphiniums are butterfly and hummingbird magnets, too! Learn how to plant, grow, and care for delphiniums.
About Delphinium Flowers
Delphinium is a genus in the Ranunculaceae family. (They’re often confused with larkspur, but these are different plant species.) There are more than 300 delphinium species, so there is quite a variety of heights, from dwarf hybrids to 6-foot tall beauties, so they can be planted in the front, middle, or back of a perennial border. The blue delphinium is most common, but varieties also come in gorgeous shades of violet, pink, white, red, and purple. They are popular in both cottage-style and cutting gardens.
Image: Edita Medeina/Shutterstock
Most delphiniums are short-lived perennials, lasting 2 or 3 years in the garden. Some varieties will bloom throughout the entire summer if the plants are cut back regularly. Other hybrids bloom from early to mid-summer and will produce a second flower display in late summer or early fall if you cut off the old flower stalk.
What’s important to know about delphiniums is that they will thrive if you meet their specific conditions. Delphiniums prefer moist, cool summers; they do not fare well in hot, dry weather or sudden wind or rain, which can knock them down. Most varieties will need staking. See more details below.
Are Delphinium Poisonous?
Yes, delphiniums are highly poisonous. If seeds and seedlings are ingested, they can cause nausea, twitching muscles, paralysis, and even death. This is mainly a concern for grazing animals such as cattle, horses, and sheep, and it is also a caution to gardeners with small children.
Growing
- Delphinium are heavy feeders. Apply a balanced liquid fertilizer starting in early spring every 2 to 3 weeks.
- Insert sturdy stake supports no later than mid-spring or when the plants reach 12 inches high.
- Do not allow the soil to dry out but avoid puddling. Water plants during the summer if rainfall is less than 1 inch per week.
- For ideal flower spikes, thin side shoots at 3 inches high, leaving 2 or 3 shoots on young plants and 5 to 7 shoots on mature, well-established ones.
- Deadhead by cutting spent flower spikes back to small, flowering side shoots.
- After delphiniums have finished blooming, cut flower stalks to the ground, and new, though smaller, flower stalks will develop. The flowers will survive the coming cold days and even light frosts. (See local frost dates.)
- Every 3 to 4 years, divide plants in spring: Remove and replant the new little plants growing around the outside of the clump. Discard the hard old heart.
Credit: Arty Alison/Shutterstock
Catherine Boeckmann
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Will the seeds winter over outside, or do I have to keep inside and germinate in the spring to later plant outside?
Hi Patricia,
Delphinium seeds need a cold period for spring germination. The recommended approach is to harvest your seeds once the flowers have all faded. At that point, cut down the stalks to the ground and hang the stalks indoors to dry. Once the seed pods begin to split (after a few weeks), remove the small seeds and store them in an airtight container in the refrigerator during the winter months. About 10 weeks before your last frost date, remove the seeds and begin the germination process indoors. Plant the seeds in evenly moist soil (just not too wet) covering the seeds with about 1/8 inch of soil. Seedlings should emerge in 21 to 28 days. Once seedlings appear, provide plenty of light. Before planting outdoors, harden off your seedlings.
Thank you for this wealth of information.
How many seeds do I need to pland in one place if I am starting them in a pot or the ground?
My delphinium is huge and extremely sturdy. The flowers are starting to fall away and I noticed what appears to be green seed pods. Can I collect these and sow them for more plants? I only have the one and it comes back every year, but no others have developed around it.
Once your delphinium flowers have all bloomed and gone away, it is time to cut the plant’s stalks to the ground. Hang the stalks, which include the green seed pods, in a spot to dry. After a few weeks, you will notice that the pods begin to brown and split. You can also hear the seeds moving around inside the pods if you give the stalk a shake. Break open the pods to remove the tiny seeds and then store them in an air-tight container or zippered plastic bag in your refrigerator over the winter. Delphinium seeds need a cold period over the winter for spring germination. You can start the seeds indoors 8 to 10 weeks before the last frost.
When you say young ones are poisonous, do you mean 'early in the Spring' young or a plant that is one or two years old, rather than a mature plant of 20+ years? Thank you.
The new leaf growth of delphiniums tends to be the most poisonous exposed part of the plant, so delphinium plants are more toxic earlier in the year than they are later in the year.
Are they poisonous if chewed by a dog ?
Yes.. (poisonous means poisonous)
... kinda like drinking gasoline. If humans can't drink it. Then any other living thing probably shouldn't drink gas..
.... next question I'm assuming
Are fires hot? Since fire burns me, will it burn my cat? Hahaha
People people people...
....humans can eat onions but dogs cant. why do you have to act like this is such a dumb question? you dont look smart, you look rude.
