If You Know Secret, Delphiniums Not Hard to Grow

Times Garden Editor

Delphiniums are true garden aristocrats--strong vertical shapes that tower above everything else, in colors that are most regal, including that most precious of garden colors, true blue. No wonder some of the favorite strains have names like King Arthur, Guinevere and Galahad.

They would probably be in every garden if it were not that they have a reputation for being difficult to grow, but they are not, if you know but a few delphinium secrets.

Did you know that they are not light sensitive? That means you can plant them at any time, though right now is one of the most favored seasons, because planted now, they will bloom in late April or May, in harmony with so many other flowers that also flower in late spring. You can, however, plant delphiniums in the middle of summer or the dead of winter. The best flowers come on plants that do their early growing when it is cool, but flowers will bloom in any weather, they will just be on shorter spikes.

Did you know that there are full-sized delphiniums and compacts? Though there are many kinds, two types are commonly available--the Pacific Giants (more properly the Pacific strain) and the Blue Fountains strain. Pacific Giants can live up to their name by growing to five or six feet or even eight on occasion. Spikes are fat and full, or should be.


The Blue Fountains (sometimes labeled Dwarf Fountains) strain grows much shorter, from three to four feet tall, sometimes even less. These too should have fat, full spikes, but don’t always.

The reason plants are not always as they should be is that they are grown from seed that is open-pollinated in fields and they do not always come true to type. Many years ago, the Pacific Giants were as uniform as corn in a field, but then they were hand-pollinated and carefully selected for their seed. Ken Dorwin, now with Hi Mark Nursery in Carpinteria, used to work with Frank Reinelt, the originator of the Pacific strain and he knows how much they have deteriorated over the years. He notes that flowers are not always double so the spikes look less full; that the height is no longer uniform; and that often they aren’t even the color they are supposed to be. But even then, there are few flowers that make such a spectacle in the garden.

It is important to note that in California we only grow delphiniums from seed-started plants--seedlings--not from cuttings. On the East Coast and in England, most delphiniums are grown from cuttings, but despite the fact that delphiniums are perennials, and that some are native to California, garden types do not grow as perennials here, but must be replanted every year--from plants begun from seed.

This is important to know because you shouldn’t waste time trying to keep the plants alive for more than a year, and you must expect some variability among the plants you purchase. You certainly do not want to throw money away on cutting grown-plants purchased from mail order growers back east.


This variability may change for the better in the near future because Dorwin is busy at work redoing the Pacific strain, so in a few years, it may once again be as flawless as it was 40 years ago. He is also working with Delphinium zalil , a yellow species, and D. cardinale , a red, in an effort to get a delphinium strain that includes red and yellow (the Swiss have already produced some small red and yellow strains but they are not commercially available).

Each Group Same Color

The Pacific strain is actually a group name for several individual strains and each group is supposed to be the same color. For instance, plants labeled as Galahad are all supposed to by white, Black Knight should all have dark purple flower, Summer Skies should have blue flowers with white “bees” (centers), and Blue Bird should be pure blue. But, since these are strains, they will not be indentical, just similar. You may find them simply identified as a mix, which means they could be any color and probably will be.

Did you know that delphiniums like lots of water? More than most flowers in fact, but here we must pass along a trick developed by nurserywoman Pamela Ingram of Sassafras Nursery in Topanga.

She has been adding those new gels to the soil that goes back into the planting hole. These gels, or soil polymers (the most commonly available is Broadleaf P4), can increase the water holding capacity of a soil by much as 400 percent, thus making much more water available to the plants in contact with it. In other words, you can give the delphiniums more water without watering them more often so other plants in the vicinity are not drowned.

Lots of Fertilizer

Looking a lot like coarse salt, the polymers swell up to the size of peas as they soak up water and store it for the plant’s use. Naturally, you want to put the polymers where they do the most good, near the bottom of the hole, and when you pull the plant out in winter, you will find that the roots have latched on to all of the polymers in their search for water.

You can probably guess just from their size that delphiniums need lots of fertilizer, and they do--another secret of success. The easy way to provide it is with a slow-release fertilizer, Osmocote being the best known.


As the package points out, this kind of fertilizer slowly releases the nutrients to the plants for as long as 120 days--"120-day continuous feeding"--so the delphiniums get their daily bread.

Be prepared for a little expense here--Osmocote costs around $8.50 for 40 ozs. and Broadleaf P4 goes for about $18 a pound--but then only the best will do for these Cadillacs of flowers (the plants themselves are going to look like a bargain at around $1.50 per 4-inch pot).

Plants Should Be Spaced

Here’s how you might plant your delphiniums this year, using this new knowledge and technology: Select a sunny spot with the best soil in the garden, or thoroughly prepare a garden bed by digging in organic amendments until a rich soil results.

The Pacific Giant plants should be spaced about a foot apart, or a little more; Blue Fountains 10-12 inches apart. Dig a hole about a foot deep and a foot across for the Pacific Giants; 10-by-10 inches will do for Blue Fountains. Ken Dorwin tells us that delphiniums have fairly shallow roots, but the depth of the hole is important to assure that excess water drains away.

Working in moist (but not wet) soil, do one hole at a time and put the soil you dig out of the hole in a big plastic bucket or basin. Add several handfuls of an organic amendment, such as Kellogg’s Gromulch to the soil in the bucket and mix it in thoroughly, breaking up any clods as you go.

Now partially refill the hole with this amended soil until it is almost full enough to support the size plant you are working with. At this time of the year, plants in 4-inch pots are the best bet; plants from packs are better earlier in the year and plants in gallon cans are only for those who are in a real hurry (you will be disappointed by size of their spikes). Try to find plants that have not yet made spikes.

Fill Around Plant


With your hands, pack down this soil in the bottom of the hole so it doesn’t settle too much later on. Dump out about half the soil that is left in the bucket and add a scoop of Osmocote (scoops are included in the package) and a teaspoon of Broadleaf P4 (it doesn’t take much) to what remains in the bucket.

Mix this all together, put some in the hole, set the plant on top and then fill in around the plant. If it doesn’t quite fill the hole, use the soil you set aside. Pack the soil sown with your hands. When all the plants are in, water thoroughly and make sure plants don’t dry out even for a moment during the first few weeks until the roots find those polymers.

This may sound complicated but it isn’t (I just did it) and work progresses quickly; it is also the kind of garden work one can savor.

There is one more thing to do if you are growing the Pacific Giants, what photographer and delphinium fanatic George de Gennaro calls “rule number 1"--immediately after planting, put in sturdy stakes to support the tall flowers.

They are going to need them as soon as they begin to shoot up (tie them to the stake as they grow) and you had best be prepared (and you do not want to damage roots by shoving in a stake later on).

Plant in Small Groups

When they finish blooming, cut the spikes back, leaving only a few leaves at the base, fertilize again (with a granular fertilizer scattered over the bed), and the delphiniums will make new sprouts in a few weeks and begin a second cycle of flowering, though this time the spikes will be smaller though more numerous.

What do you plant delphiniums with? I always think of delphiniums as the church steeples in a village of other flowers, and it doesn’t take many to make a statement. I plant them in small groups of five.

Try them with lower bushy flowers, such as Shasta daisies (which can be planted now and will bloom with the delphiniums) or coreopsis or just about any other perennial. They are equally elegant behind summer annuals such as gloriosa daisies, zinnias and marigolds though they will probably flower before these reach their peak. De Gennaro plants them behind lilies. Whatever you choose, you will not be disappointed, and you will probably never consider planting flowers again without the royal company of the regal delphiniums.