Use these tips to grow and care for these favorite tall, flowering perennials in cold climates. Find out how to germinate the seeds, get second blooms, protect the plants from wind, and keep them growing back year after year.
Delphinium | Genus: Delphinium
Delphinium Growing Guide
• Hardiness zones 3a to 8b
• Full or part sun
• Well-draining loam is best
• Native to North America and African mountains and considered non-invasive
• Chill dampened seeds for better germination
Shop Online: Buy delphinium seeds at Botanical Interests (US shipping)
I officially became a gardener the day I visited a local garden and saw a raised bed filled with tall, blue, gorgeous delphiniums. I just knew I wanted them in my yard (not yet a ‘garden’) and I would do whatever it took (organically speaking) to have them. They come in several colors—blues, purples, reds / pinks, yellow, white—but it was the blues that had me at hello.
Since then, my repertoire has expanded to include dozens of different flowering perennials suitable for a cottage-style garden.
Delphiniums originate in mountainous foothills in North America, and higher mountain regions in tropical Africa.
This is why they do best in climates with four seasons: the winter chilling period is essential to trigger new growth in the spring.
Here in southern Canada, they are a perfect fit. If you are in the southern United States it will be a struggle to keep them happy but any cold climate could work.
Delphinium Plant Facts & Growing Tips
Delphiniums are tall, flowering perennial plants (they grow back every year) suited to cold climate gardens (hardiness zones 3 to 8). They can reach heights of 5-feet tall (2m) in the growing season but, combined with the big flowers, this can also mean they get top-heavy. For this reason it’s wise to start the growing season with some sort of support in place to prevent the wind from bending or breaking the stems. You might use bamboo stakes and twine or a tall, modified peony cage.
Light & Soil
You can grow delphiniums in sun or part-shade. The best soil is well-draining and neither too sandy or clay-based. My own soil is very sandy and the delphiniums only really took off after years of adding a lot of organic matter to the soil which improved the soil structure.
If you are growing from seed, the most important tip is to cold stratify your seeds for weeks or months prior to germination time. This means exposing the seed to moist, cold conditions to stimulate growth. This article describes an easy way to prepare the delphinium seeds in your fridge or freezer.
If you have existing plants, you can also propagate them from basal root cuttings in early spring or by dividing the root ball of a large plant.
Delphinium flowers are quite long-lasting, staying in bloom for weeks on end. During this time you will enjoy visits from various pollinators including butterflies and bumble bees.
Blooms times depend on the variety—this could be from late spring onward.
Gardeners in Florida often ask if delphiniums can grow in their climate. Because these plants originate in the mountains and that is a tropical climate, the answer is usually no. There are, however, some gardeners who have found certain varieties that tolerate their heat and humidity so, if you are in that region, you could ask at local nurseries for suggestions. If grown as perennials, they would also need exposure to cold in the winters to mimic their native growing conditions.
If you want a second set of blooms within the same growing season, cut back the flower stems as the first flowers are starting to fade. Fewer, but some second blooms will make an appearance if there is enough time before first frost.
|Genus||Delphinium (from the Latin word for ‘dolphin’)|
|Cultivars||Elatum hybrids, belladonnas, grandiflorums|
The different genus Consolida (an annual) is also commonly called ‘larkspur.’ Make sure you’re buying delphiniums!
|Origin||Native to northern hemisphere and mountains in tropical Africa|
|Height||4-60″ tall | 10 cm to 2m tall|
|Spacing||18-24″ | 45-60 cm|
|Light||Sun or part sun|
|USDA Zones||3a to 8b (they may wilt in heat)|
|Flower times||Late spring, summer | deadhead for second blooms|
|Colors||Purple, blue, red, yellow, white|
|Soil||Moist, well-drained loamy soil is best; clay and sand should be amended|
|Fertilizer||16-16-16 kelp and seaweed extract (I do not use any in my garden but I see this recommended)|
This is the only example I could find on Amazon.
|Pollination||Butterflies and bumble bees|
|Propagation||Seeds – need cold stratification using these tips to germinate.|
Root division (cutting root ball)
Herbaceous stem cuttings (in spring before flowering)
|Toxicity||All parts are toxic to humans if ingested; skin irritant; poisonous to cattle|
|Diseases||Bacterial rots including black leaf spot and bacterial blight. |
Fungal diseases including crown rot, powdery mildew, mosaic viruses, fusarium wilt and canker.
|Pests||Root-knot nematodes, aphids, mites, cutworms, stalk borer, larkspur leaf miner.|
|Trivia||The juice of Delphinium consolida can be mixed with alum to produce blue ink.|
Delphiniums in My Garden (Ontario, Canada – zone 6b)
- Black Knight Pacific Giant Larkspur Delphinium | Delphinium x elatum ‘Black Knight’
- Delphinium nudicaule ‘Laurin’
- Delphinium ‘Guardian Series’
- Guardian Delphinium | Delphinium ‘Guardian Blue’
Frequently Asked Questions About Delphiniums
1How do I know if I can grow delphiniums where I live?
The best hint is to check if other (successful) gardeners are already growing them in your area without babying the plants. If they grow easily without special accommodations, that’s a good sign.
Before proceeding, check your growing zone. Delphiniums originate as mountainous plants and do best in a climate that provides a cold (near or below freezing) winter. This helps trigger seed germination and flowering in spring.
To find your growing zone, use the following sites:
Generally speaking, delphiniums grow in zones 3a to 8b. However, each hybrid or cultivar is unique and may only be suitable for a narrower range of zones. I get emails from gardeners in the southern-ish United States who struggle to keep delphiniums happy when heat is constant even though they are in zone 8 or cooler. Also, always check plant tags before purchasing plants for recommended growing conditions.
A good, local garden nursery is a great resource for plant information. If they are growing and propagating the plants in your zone, be sure to ask for their best tips and plant recommendations.
2Do delphiniums require any special care?
The beauty of delphiniums is their tall stature and mass of blooms. I have the best luck when I grow delphiniums in a sheltered location (here in Ontario, Canada, zone 6b) where they are protected from strong winds and direct, hot summer sun. A strong wind won’t kill the plant but it can snap the flowers off, which defeats the purpose of growing them (unless you want accidentally-cut flowers).
Leggy delphiniums benefit from supports. This could be bamboo stakes with twine loosely secured around the plants, or tall peony cages placed on tall supports.
Also, when selecting plants, look for nice, thick stems. There are many beautiful delphinium cultivars, but some of them have massive flowers on rather thin stalks and these can easily fold or collapse, killing off the flowers. Tragic, really.
3Should I fertilize my delphiniums?
We’ve been told for years to routinely fertilize our gardens by—surprise!—companies that make plant fertilizers. But what your plants need depends on the existing nutritional content of your soil and the plant’s ability to use it.
I always recommend getting your soil tested to have a basic understanding of the current nutrient levels and any deficiencies. This way you’re not guessing what’s needed or adding surplus which can runoff and mess up our waterways.
While your garden will not be the same as mine (or anyone else’s), I just top dress my garden beds with homemade compost topped with fine wood mulch each year and that’s it.
Assuming your soil actual needs it, many advise to use a 16-16-16 kelp and seaweed extract fertilizer because delphiniums are heavy feeders. Whatever product you choose, read the entire label, and understand any environmental effects.
I never use commercial pesticides or fertilizers because I want to keep things eco-friendly and know I can grow food anywhere in my yard without worrying about any product side effects.
4Can I grow delphiniums in containers?
Yes. You will need proper container mix made for flowering perennials and choose the largest container you can manage—at least a foot tall and wide for one plant.
You may need to use fertilizer or replace most of the container mix each year to ensure the plant has the nutrients it needs to grow and bloom.
And, you will need to ‘over-winter’ the container to ensure the soil and plant do not freeze. This means moving it to a protected location during the winter. This post on over-wintering fig trees outlines the steps.
5What is the best way to start new delphinium plants?
If you want to propagate new plants from existing ones, the fastest way is to divide a large (mature) plant by digging it up and splitting/cutting the root ball in two (or more pieces).
Another method is to take ‘basal’ root cuttings in spring. This involves partially digging up the plant and taking a section of the roots for propagating in a container. There’s a specific window of time for this which I famously forget about each spring.
For germination by seed outdoors as nature does it, in autumn, toss some seeds in your garden bed, cover them lightly with soil, mark the spot, and leave them to germinate in spring.
If you plan to start your delphinium seeds indoors see these tips for getting delphinium seeds to sprout faster using cold stratification.
6How can I get a full-season of blooms from delphiniums?
Delphiniums are known to produce second blooms. The theory is that if you cut back first blooms as soon as they have finished, the plant can direct all of its energy into new growth.
When the late spring flowers have started to fade, trim most of the flower stalks down to their lowest adjoining main stalk. You should get a second set of flowers before fall frosts set in.
7My garden is windy. Is there a way to grow delphiniums without the wind breaking them?
Yes, there are several tips.
First, choose delphiniums that have traits that withstand wind. There are some dwarf varieties with nice thick stems and dense flower heads. Look for the Delphinium Blue Fountains Group. They are one of my top favorites with their gorgeous blue colors.
Always stake your delphiniums or offer some sort of support—at least half way up the stalks—to help hold the plant steady when it’s windy.
Long-term, add wind breaks like evergreen trees or shrubs or some other structure to block prevailing winds.
Good luck with your delphinium growing and I hope you enjoy them as much as I do.
~Melissa the Empress of Dirt ♛
Seed Starting for Beginners
Sow Inside Grow Outside
by Melissa J. Will
Everything you need to get started with indoor seed starting for indoor and outdoor plants. Grow what you want—any time of year!
This ebook is a digital file you save to your device (not a physical product).
$5.99 US | PayPal, Credit Card, Apple Pay
PDF Format | About Ebook