Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
I have never had any luck growing delphinium in my Zone 6 garden. The summers here in NJ are just too hot for them. Delphinium like cool summers. A good substitute (and look-alike) is larkspur.
What is Larkspur?
Larkspur (Delphinium consolida) is an annual flowering plant that is native to Western Europe, the Mediterranean and Asia. It is a member of the buttercup family and related to delphinium. In fact, larkspur looks very similar to delphinium. Both have flowers on tall stalks, but delphinium flowers are more closely packed on the flower stalks. Larkspur has fewer flowers per stalk. Both have flowers that are white, blue, purple or pink. The foliage is also different. Delphinium have large deeply cut leaves while larkspur has airy, feathery leaves. The biggest difference is that delphinium are perennial. Larkspur is an annual.
Larkspur are drought tolerant plants. They have long tap roots so they do not transplant well. They grow best in sun, but will tolerate a little shade. When grown in the shade, the flower stalks are weaker and will need support to prevent them from falling over from the weight of the flowers. They also will not grow to their full 3 to 5 feet height.
Larkspur are cool season plants, growing and blooming in the cool weather of spring. They readily re-seed themselves in your garden so you can enjoy the blooms for many years. Thanks to their drought tolerance and self-sowing, they have naturalized in the landscape.
For those of us living areas where deer are a problem, we plant larkspur for their looks and because they are deer resistant.
Why are They Called Larkspur?
Larkspur got their name from the shape of their flowers. There is a “spur” sticking out of the back of the flowers that was said to resemble the claw of a lark. The flowers have also been called lark’s claw and lark’s heel. In medieval times, they were known as knight’s spur for their resemblance to the spurs on knights’ armor.
Is Larkspur Poisonous?
Yes, all parts of the plant, including the seed, are poisonous. They contain highly toxic alkaloids which are poisonous to humans and most animals. In areas where they have escaped our gardens and naturalized in the fields, they have been known to kill cows who graze on them. Surprisingly, sheep are resistant to the toxin so farmers often send sheep into a pasture to graze all the larkspur before allowing their cows into the field.
How to Grow Larkspur From Seed Outdoors
Most gardeners grow larkspur from seed rather than purchasing plants. In the warmer parts of the South, you can sow your seeds in the fall for spring flowers. Zone 7 and north, sow your seeds outdoors in the early spring after your last frost. Sow them ¼ inch deep. Make sure that they are covered because they need darkness to germinate. Germination should occur in 2 to 3 weeks. You need to sow the seeds early in the spring, because the seedlings need temperatures below 55⁰F for the first 6 weeks of growth. In fact, the seeds will not germinate at all when temperatures reach the 60’s. Make sure that you sow your seed where you want the plants to grow. Due to their long taproot, larkspur do not transplant well.
How to Start Larkspur Indoors From Seed
If you prefer to start your seeds indoors, you will need to cold stratify them. Larkspur needs a period of cold to start germination. Six weeks before your last frost, plant your seeds ¼ inch deep in a container and place the container in a plastic bag. The plastic bag is to prevent the soil from drying out while it is being chilled. Refrigerate for 2 weeks. After 2 weeks, remove the container from your refrigerator and place it in a sunny window in a cool room. The soil must remain below 55⁰F or the seeds will not germinate.
The seeds should germinate in 2 to 3 weeks. The seedlings need temperatures below 55⁰F so keep them in the cool room until you are ready to transplant them into your garden after your last frost. Transplant carefully trying not to disturb or injure the taproot. You might want to start your seeds in individual peat pots or other biodegradable pots so that you can plant the whole thing, pots and all, in your garden and avoid injuring the taproot.
Using Larkspur in Flower Arrangements
Larkspur is often used in flower arrangements, both fresh and dried. For a fresh arrangement, harvest the flowers when 1/3 of the flowers are open on the stalk. Keep them cool until you are ready to use them. They will last 5 to 7 days in a vase.
An easy way to keep your larkspur cool until you are ready to use them is in a vase of water in your refrigerator, similar to how florists keep their cut flowers fresh in coolers until they are ready to add them to arrangements.
Larkspur are also popular as a dried flower in arrangements because the flowers keep their beautiful colors after they are dried. For a dried arrangement, harvest the flowers when most of the flowers on the stalk are open. Be sure to harvest before all of the flowers open because when all are open, the first ones to open will begin to drop within 24 hours. Dry them using your usual method to dry flowers.
Questions & Answers
Question: Is Larkspur suitable for zone 10?
Answer: Zone 10 is the extreme southern growing zone for larkspur. They are a temperate zone plant that prefers cool summers and mild winters. Your summers may be too hot and the plants may struggle in the heat.
© 2014 Caren White
Caren White (author) on July 13, 2014:
Flourish, I was surprised to learn that such a fragile looking plant could kill something as sturdy as a cow! Thanks for reading.
Caren White (author) on July 13, 2014:
No, I'm afraid that they will only grow through zone 9 which is sub-tropical. Thanks for reading!
FlourishAnyway from USA on July 13, 2014:
I didn't know about the potential toxicity. Very interesting. They are a beautiful flower.
Raimer Gel on July 12, 2014:
Will it thrive in tropical countries too?