Delphinium, Diva of the Mixed Border

I say ‘diva’ because delphiniums are attention-grabbing, gorgeous garden stars, but also notoriously temperamental to grow and sustain. Their finicky needs demand high maintenance and a considerable tolerance for unreliability. Since they are arguably one of the most beautiful perennials on the planet, we “delph” lovers grudgingly carry their water (literally!) in hopes of a spectacular show. If you think you’d like to try growing a few, read on.

Delphinium or larkspur?

You may know this plant better colloquially as larkspur. But the umbrella term “larkspur” often lumps both delphinium and larkspur cultivars under the larkspur (or candle larkspur) name. Both have striking spires of pink, blue, lavender or white flowers. True larkspur is the annual form. Delphiniums look very similar but are perennial. Since both types are often listed as “candle larkspur,” be sure to check the tag for hardiness. Lots of people buy larkspur at nurseries thinking they’re getting a perennial delphinium, only to be disappointed when nothing comes up the next season.

There are some shorter delphs on the market now (Belladonna series is one) but most grow up to five feet tall, have bigger blooms and more densely packed spires than the true larkspurs. Another way to tell them apart is larkspur flowers are airier and mostly pastel in color; you will often see them in cut flower stalls or at the supermarket.

I will focus on tall garden delphiniums here.

Worldwide there are 370 delphinium species, all poisonous, native to temperate areas of the northern hemisphere. Most originated in the Himalayas and China. Both species and hybrids prefer cool, moist conditions with low humidity and good protection from wind.

Of course we rarely have low humidity or cool summers in Pennsylvania anymore, and our storms can be devastating. Still, it is possible to grow delphiniums with some caveats.

How to Grow

After consulting a number of authoritive delphinium sources online and based on personal experience, here are my suggestions. Luckily it’s not necessary to pamper them quite as much as the literature suggests; I’ve had decent luck with only half-hearted care. So even if you can’t devote much time to them, consider growing them anyway.

It is best to start with potted specimens for transplant in spring, after all danger of frost. I don’t recommend starting these plants from seed; delphiniums can be quite challenging to propagate that way unless you’re a seasoned seed-starting wizard.

Situate delphiniums in at least six to eight hours of sun, with a bit of shade during the hottest part of the day if possible. Place toward the back of the border or near a wall or fence for protection from wind. Space at least a foot apart to ensure adequate air circulation.

Being heavy feeders, delphiniums need rich moisture-retentive soil and will benefit from frequent fertilizing. They like it on the alkaline side, so mix in a bit of lime if your soil is at all acidic. Add organic material or compost at planting time. Place the crown even with the soil line; anchor it snugly and mulch afterward to help keep the roots cool. Avoid packing mulch against the crown or stems; delphiniums frequently succumb to crown rot. (A little pea gravel around the stems will mitigate this.) Top dress with a bit of compost in fall.

Feed monthly with a balanced liquid fertilizer all season; keep watered during dry periods. Delphiniums are susceptible to many pests and diseases so inspect them regularly. Treat promptly if a problem develops so it doesn’t spread.

While delphiniums are considered perennial in zone 6, I find that despite all this pampering, they are still short-lived. Cultivars rarely survive for me more than two winters. So, I treat mine as if they were biennial, often buying replacements the second season as insurance against loss the next. Delphiniums rarely self-propagate. Once they die out they’re gone.

Are you still with me? There’s more…

Stakes and Supports

Young plants twelve inches and taller must be staked or caged. Staking is no guarantee, but it greatly increases the odds of having your spires remain upright after thunderstorms. A semi-sheltered spot out of the prevaiing wind is ideal. Even so, stake, stake, stake!

On very young plants, allow just two or three flower shoots to develop; remove the rest (if any). On mature plants, limit to no more than seven. This will ensure a better display on the remaining stalks.

The trick is not to tie the stems so tightly they can’t move, yet not so loosely they slouch and sprawl. I’ve tried everything from single stakes to peony cages to wire hoops; all work to a degree. Lately I’ve had luck with a circular tomato cage, which is both narrow enough and tall enough to accommodate several spires at once.

TIP: Using soft twine, tie taller stems in about halfway up. As they grow, tie them again just under the flower buds, allowing some slack. (A little stem movement is necessary to develop strength and prevent sharp snaps.) The benefit of a circular cage is the curvature allows for several inches of stem motion while still providing excellent support.

Don’t force an unruly stem; use another stake. The stems are hollow so it doesn’t take much to put a dent in them. It’s just as easy to break one tying it to a stake as having a storm do it in. Once broken or badly bent there’s no recourse but to cut down the damaged spire. (It will last several days in water in the house if it’s started to open. Keep toddlers and cats away, these plants are poisonous.)

Losing a large spire is heartbreaking. It happens to everyone, so don’t get discouraged. I told you these divas can be fickle!

Cut back for more blooms

After the intial spires bloom, cut down the spent stalks to the side shoots or basal clump. Fertilize again with a balance liquid fertilizer (if you think of it; I often forget). This will encourage a second, shorter rebloom later. While not as impressive as the first, a second flowering stretches the delphinium season into July and even August.

Which cultivars?

Most perennial hybrids are improvements on the straight species delphinium elatum. There is usually little choice at nurseries, and mail order houses carry just a handful of cultivars. Go with what you can find that you like.

Delphiniums come in fantastic colors, none more sought after than true blue. From pale shades to turquoise to cobalt and navy, they have perhaps the broadest range of blues in the flower kingdom. They also come in lovely lavenders, purples, raspberry pinks, whites, and bicolor blends.

Some are double; most have a contrasting eye called a bee, which can be white or black. The intense cobalt blues and deep purples are what they’re best known for, as well as white. Whichever you choose, plant at least three plants (same or different shades) together for the best display. Several plants are a good hedge against breakage, too.

Millenium is a new series from New Zealand, bred for better tolerance of heat, humidity and disease. They come in all colors. I’ve grown Blue Lace, a frilly looking double, but I’m not sold on it.

Guardian is a new series featuring a medium-tall height (2 – 4 feet) bred for dense, uniform flowers that bloom earlier than most. I can attest that they do bloom earlier and the racemes are very dense.

The best-known tall strains offered in the US are Pacific Giant and Blackmore & Langdon (B&L). They average five feet tall and come in all colors. I’ve grown both; mine typically reach a modest three to four feet. No doubt they would get taller if I fed them more.

Years ago, I saw a huge stand of Pacific Giants in Luther Burbank’s California garden towering well over my head. They certainly have the potential to reach six and even seven feet under optimal conditions. But don’t count on it in Pennsylvania unless you have a good source of aged horse manure and lots of time to baby them!

I enjoy delphiniums’ lovely verticality as much as their color, so I no longer grow the shorter Magic Fountains or Belladonnas. If you have a small space, by all means try them. Magic Fountains gets two feet tall; Belladonnas are more delicate with less substance, but have excellent color. They mix well throughout the garden; just don’t put the Belladonnas where their short height could get lost.

Companions

Dephiniums are often featured with roses, phlox, trumpet lilies, tall salvias, catmint (nepeta) and bellflowers. They would also look fetching with hollyhocks, flowering tobacco (nicotiana) Lime Green, and the white dwarf hydrangea Bobo. By and large they do best with plants that like the same conditions they do, so let that be your guide.

Choose a cultivated spot where you can appreciate their beauty and tend to them easily. A high stone wall or a curtain of deep green foliage behind (as in the photo above) are particularly effective at highlighting their exquisite blooms.

There’s really no “bad” way to display delphiniums — wherever you put them, they will make your garden the envy of the neighborhood!

So there you have it. Delphs aren’t the easiest beauties to grow for sure, they are certainly among the most spectacular. Good luck!