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Planting, Growing, and Caring for Delphiniums
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鈥檙e 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鈥檚 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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I have seen delphiniums on sale now. Can I plant out now?
Hi Mary,
It’s too late to plant delphiniums now; they should be planted in the spring. Delphiniums don’t like hot, dry weather like that of the summer.
I know it's not ideal, but I have a delphinium in a shady garden that needs to be moved. The whole bed needs to be dug out and redone. My question is, will it be worth the effort, or will I kill it? It's a nice big plant, and I do have a better location for it. It is blooming, but the stems all fell over, and are laying flat. So I thought I would just cut them off totally, then move it. I am in zone 3b, and we are having 80degree days, 60 degree nights.
There may be several factors that put the plant at risk, not moving it alone. Soil conditions are key: well draining and alkaline being paramount, and a thin layer of compost each pring, followed by 2 inches of mulch to help retain moisture (soil should not dry out) and deter weeds. Lifting and dividing should be done in the spring; can you wait?? These plants are not fond of heat. So that and lack of sun (they’ll tolerate light shade) could be the reason/s its flagging. Remember, if you lose it, you can get another one.
I have just resented planted my first delphinium and it has been growing great. The top has blooms on it but has not bloomed yet. We had two days of downpours getting maybe 5inches in two days. Now the top of my flower has dropped over. What do I need to do? Will it snap out of it?
If the soil is soggy, the blooms will drop. Let the soil dry out and the plant should recover. Also, it helps to stake delphiniums to prevent damage in a rainstorm. Use some natural twine around the plants, just below the flower heads, without actually tying them up.
Can I plant in a large pot? Is it an annual?
Delphiniums are perennials, so they will come back each year as long as they are hardy in your . You can plant delphiniums in pots, but be sure to use a pot that has a drainage hole and has loose, well-draining soil.
Hello! We recently had some heavy winds and I was unaware to stake my delphiniums in the spring so they all tipped over. I tried lifting a couple but two broke at the base so I stopped moving them. Can a person still salvage them somehow? Will broken ones still come back next year?
Thanks!!
Good question! If your delphiniums were allowed to bloom normally, you would cut back the stalks after the flowers died. Your delphiniums should have no problem coming back next year.
