The Risks and Rewards of Growing Delphiniums

Delphiniums are useful for creating height in containers or small gardens. They flower in pink, white, or blue, and there are also dwarf types. Buy plants and seeds here. Companion plants for Delphiniums.

What would an herbaceous border be without the colorful spires of  a Delphinium springing up like a floral jack-in-the-box?  This perennial garden classic blooms in several shades of blue, white, and pink.  There are 12 inch tall dwarf cultivars and 7 foot towering giants, with most plants falling somewhere in between these two extremes.

These vegetative exclamation points provide a vertical accent in garden beds or container plantings without taking up much "floor" space.  The dwarf forms contribute intense shades of blue close to the ground.

But all of this garden excitement does not come to us without risk.

Although easy to grow--from plants or seeds--Delphiniums have special needs:

  • They require more nitrogen than nearly any other garden plant!
  • They are shallow-rooted and may be heaved out of the ground as it freezes and thaws in the colder end of their growing range.
  • They are prone to crown rot during wet weather.
  • Tall types may blow over, or snap in the wind, if not properly staked.

How to Grow Them so as to Avoid these Potential Problems

Purple and white delphniums blooming in a garden.

Delphiniums grow best in zones 3-7 where summers are cool.

In warmer climates, they may be grown, from seed,  as annuals.

  1. Site the plants in full sun.  This is especially important for the taller kinds as strong light encourages upright growth.
  2. Add composted manure to the planting area prior to setting the plants in. These heavy-feeders perform best in rich, free-draining, moisture-retentive soil.
  3. Space the plants 2-3 feet apart in the bed.  Crowding hinders air circulation and leads to disease problems.
  4. Apply a light mulch of straw to prevent heaving in winter and conserve soil moisture in summer.
  5. Feed the plants at least twice per season with a balanced fertilizer. Begin feeding in the spring once the plants have achieved 4 inches of new growth. Fertilize the plants again 5-6 weeks later.

    After this you will need to watch the plants and continue to feed as needed.

    Overfeeding can lead to insect and disease problems.  The leaves of underfed plants will yellow.  To remedy this, apply fertilizer every 10 days until new growth (the old leaves will not recover) comes in green.
  6. Water copiously as flower buds are developing and throughout the blooming period.  Never expose the plants to drought.
  7. Stake taller varieties when they reach a height of 3 feet.  Place 3 five-foot stakes around each plant in a triangle pattern.  Tie soft twine around the stakes at 1 foot intervals as the plant grows.  You can also stake individual flower spikes if they are particularly heavy or brittle.
  8. Lift and divide clumps, when they become too large, by cutting them apart with a sharp knife.  Each division should have 4 or 5 shoots.  Pot or replant the divisions immediately.

How to Get More Flowers:

If you clip the bloom stalks off as soon as the flowers wither, your Delphiniums will bloom again in the fall.

Growing Delphiniums from Seed

Delphinium, Fantasia Mixed Colors 1 Pkt. (100 seeds), Plants Also Available

If you sow the seeds indoors between February 1st and April Fool's Day, the resulting plants will bloom in late summer or early fall of that same year.  Hot zone gardeners may need to alter this schedule so that the plants do most of their growing and blooming during the cool season.

Sow the seed in flats, in rows 2 inches apart.  Cover them, just barely, with soil.  Once the seedlings are large enough to handle easily, move them into individual pots.

Grow them on under fluorescent lights until the weather warms enough to plant them outside.

Tip for Florida Gardeners:

Sow the seeds in flats, outdoors in the shade,  in September or October and let the plants grow through the winter.

Move the seedlings into bright light and keep them moist as they develop.  Plant them out in late November.  Expect flowers in February or March.

The cottage garden annual, larkspur (Consolida ambigua) is a Delphinium look-a-like.  Where temperatures are extreme, it may be easier to plant larkspur instead.

Plants for Sale

3' Tall Delphinium, Guardian Blue
12" Tall 'Summer Stars'
5' Tall 'Pink Punch'
Dwarf Delphinium, Blue Butterfly
Dwarf 'Summer Mornings'
4-5' Tall 'Purple Passion'
Dwarf 'Summer Nights'

Dwarf Delphinium 'Summer Blues'

6' Tall 'Blue Lace'

Companion Plants for Delphiniums

Take Advantage of These Deals:

Iris, Black
Bellflower, Dalmation

Plants with silvery or white leaves (Artemesia, Dusty Miller) make especially fetching neighbors for Delphiniums.

As their lower stems can become untidy toward the end of the growing season, tall types benefit from being planted behind shorter plants which can hide their legs.

If you are designing a blue border try: hardy Geraniums, midnight blue Irises, sky blue flax, and hazy drifts of purple catmint.

In a cottage garden, crowd them in amongst: sweet peas, hollyhocks, foxgloves, blue cornflower, and mounds of purple bellflower. 

They have an affinity for pink or white roses.  The softer shades of yarrow and Phlox also compliment them.

Strawberries and Delphiniums Do Not Mix

Strawberries are a host plant of the cyclamen mite which also like to munch on Delphinium leaves.  Their doing so will stunt the plants and mark them with black streaks and blotches.

Other Perennial Border Favorites:

Black-Eyed Susans

Amsonia tabernaemontana  'Blue Ice'

'Fairy' Roses


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