The Complete Guide to Growing Delphiniums in Your Garden

Use these delphinium tips to grow and care for these favorite tall, flowering perennials in cold climates. Learn the best growing conditions, care tips, how to propagate, and keep them growing back year after year.

If you want to start your plants from seed, use this trick to germinate delphinium seeds.

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Delphinium Growing Tips

If you have a four-season cold climate garden, these tips will help you get started growing these beautiful plants.

Where can delphiniums grow?

Native to cold climates in North America and mountainous regions in Africa, most delphiniums suit hardiness zones 3 to 7 here in Canada and the United States.

If they are suitable for your region, you will likely find delphiniums at your local plant nurseries.

Are delphiniums annual or perennial?

Delphiniums are herbaceous perennials. This means their stems and leaves die back in fall and winter. Come spring, as temperatures and light increases, new growth emerges from the roots.

Larkspur is an annual relative of delphiniums.

What conditions do delphiniums like?

• Light | Full or part sun. Many do not tolerate persistent, intense heat.
• Soil | Well-draining soil.
• Soil pH | Ideal range is 6 to 7.5 pH.
• Water | Moderate, consistent moisture is best. Do not allow to dry out.

Do delphiniums require fertilizer?

Whether or not your delphiniums (and other plants) need fertilizer will depend on your unique soil conditions.

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.

I enrich my soil with homemade compost. Some eco-friendly gardeners use a fertilizer like kelp or seaweed and fish extract.

When do delphiniums bloom?

Flower times can vary but, generally, delphiniums start blooming early to midsummer in full sun locations. This may take longer in part-sun locations.

Should I cut back delphiniums after they bloom?

Delphiniums do not require cutting back or deadheading but there are reasons why you may want to.

If you want a second set of blooms, cut back the original flower stems as the first flowers start to fade. If there is enough time before the growing season ends, your delphinium may flower again.

If you want to save seeds or let the plants self-seed, do not remove old flowers—that’s where seeds are produced. To “self-seed” means to let the seeds germinate wherever they land in the garden.

How tall do delphiniums grow?

Some delphiniums like Pacific Giants grow between 4 to six feet tall. There are exceptions including some short, stout varieties like the ones in this Butterfly Blend that stay under 3-feet tall. The dwarf varieties are a good choice in high wind areas. Some taller varieties seem to have exceptional genes and can reach upward of 8-feet tall.

What is the best way to support delphiniums?

Tall wood or metal stakes, trellis, or cages are all options. How well they stay in place may depend on your soil. I need to bury stakes quite deep in my sandy soil to keep them stable.

It helps to put stakes in place early in the season or at planting time. Add loops of loose twine as the plant grows.

How can I prevent delphinium stems from breaking in windy conditions?

Along with providing stakes to support the plants, this may help:

• Choose varieties with thick stems.

There are some dwarf varieties with nice thick stems and dense flower heads. Look for the Delphinium Blue Fountains Group (gorgeous blues!) or this Butterfly Blend Heirloom Delphinium mix.

• Grow delphiniums in sheltered locations that provide natural wind breaks.

What pests and diseases affect delphiniums?

Pests | Root-knot nematodes, aphids, mites, cutworms, stalk borer, larkspur leaf miner.

Diseases | Bacterial rots including black leaf spot and bacterial blight.
Fungal diseases including crown rot, powdery mildew, mosaic viruses, fusarium wilt and canker.

Can delphiniums grow in containers?

Yes, you can grow delphiniums in pots. You will need proper container mix made for flowering perennials and the largest container you can manage—at least a foot tall and wide for one plant.

You may need to use fertilizer and/or replace most of the container mix each year to ensure the plant has the nutrients it needs to grow and bloom.

Overwintering will ensure the plant does not freeze. This article on how to over-wintering potted trees outlines the steps for storing the containers in fall, winter care, and reintroducing to outdoor conditions in spring.

Do delphiniums spread?

Delphiniums do not spread by runners the way other plants like raspberries do. Delphiniums can spread by self-seeding. Also, as the young plant matures year over year, the root ball will increase in size resulting in more foliage and flowers.

How do you propagate delphiniums?

Seeds | Prior to germination, delphinium seed require a period of cold stratification. This occurs naturally in the wild or you can follow these steps to cold stratify the seeds at home.

You can also use this winter sowing method in closed containers for delphinium seeds or this easy winter method.

To collect seeds, use these seed saving tips and tips for safely storing seeds indoors for next year.

Cuttings | In early spring, you can propagate basal root cuttings. 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.

Division | Prior to flowering in the growing season, division is a good option to create new plants from well-established ones. Dig up the entire root ball and divide into one or more separate plants.

When is the best time to plant delphiniums?

The best time to plant a delphinium plant is in spring when the soil is moist, conditions are not too hot, and before flowering. You can also plant in fall after flowering if there are 4 to 6 weeks for roots to establish before first frosts.

What companion plants go with delphiniums?

The idea that plants have friends and enemies is basically garden folklore. For delphiniums, and all plants, focus on providing the right growing conditions including light, soil, water, and spacing. Together these will give your delphiniums their best chance of success.

Do delphiniums attract pollinators?

While flowering, delphiniums are attractive to various butterflies and bees.

Can I grow delphiniums in Florida?

In general, no, delphiniums are not suited to sub-tropical or tropical conditions. They are native to cold climates with freezing winters and may die off in intense heat.

That said, some gardeners have found varieties that tolerate the heat and humidity in parts of Florida. If you want to try, ask at local plant nurseries for tips and recommendations.

Resources

About Delphiniums

Family	Ranunculaceae
Genus	Delphinium (from the Latin word for ‘dolphin’)
Species	Approximately 300
Cultivars	Elatum hybrids, belladonnas, grandiflorums
Common name(s)	Larkspur 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
Type	Perennial
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
Attracts	Butterflies and bees
Propagation	Seeds – need cold stratification using these tips to germinate Root division (cutting root ball) Basal 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

~Melissa the Empress of Dirt ♛