English Delphiniums

Spectacular English Delphiniums

English gardens have long been graced with spectacular delphiniums, 6 to 8 feet tall, exquisite in color and form, of upright growth and outstanding winter hardiness, the results of decades of patient hand-pollination and back-crossing with named British clones. We at Log House Plants have worked for several years with Lynne Rathbone and the Delphinium Society of Great Britain to bring these plants to the Pacific Northwest, and we are happy to introduce them to you now.

The plants we offer are starts from hand-pollinated British seed. They will thrive in deep, moist, rich, well-drained limy soil, in a location that is sunny but not baking-hot. As they bloom this first summer, you can mark your favorites, and next spring propagate your own clones by rooting sprouts from the crown. Cut one or two shoots as soon as they emerge, before they become hollow, and leave the other shoots to grow and bloom. Be sure to include a piece of the woody crown with each cutting, and root.

We welcome you to join us in bringing back the splendor of the “True Monarch of Perennials”, a splendor lost during years of careless breeding in the U.S. and elsewhere. The deterioration that delphinium varieties such as ‘Pacific Giant’ have experienced is true of many flowers, vegetables, and herbs, as treasured varieties slide far downhill or disappear completely. As home gardeners, we can improve this situation by letting the U.S. seed industry know that we want the finest seed possible, in the most diverse range of species and varieties, and that we want U.S. seed companies to get their act together and produce it! We can also take matters into our own hands by participating in Seed Savers International, an organization of home gardeners who save and swap seed of rare varieties of annual and perennial flowers, vegetables, and herbs. (Seed Savers International, 3076 North Winn Road, Decorah, Iowa 52101.)

The Proper Cultivation for Growing Great English Delphiniums

Growing English Delphiniums may require a little extra effort, but the results will amaze you.

SOIL — Delphiniums can be grown successfully in neutral, alkaline or in acid soils, but they require a fertile, friable and nutrient retentive soil that has excellent drainage. They can be grown successfully in any soil as long as it is not waterlogged, especially in the winter. Enriched soil and a raised bed for good drainage is ideal.

SITE — Delphiniums prefer full sun. During the growing season, they require a lot of water. Do not plant them under large trees or too close to a wall or tall hedges; too much shade will cause the flower spikes to become tall and spindly. At least six hours of full sun is required daily. Protection from very windy sites is obviously an advantage. Select your site carefully, because mature delphiniums do not like to be moved.

PLANTING — Start with a prepared bed that has been enriched with manure and compost and is not weedy. Dig a hole and add two large handfuls of bonemeal, mixing it well in the hole. Position the plant so that the base is at ground level and firm in very well so that no pockets of air exist around the plant, and the plant is standing firm. Plant the delphiniums in groups of three, each at least two feet apart. Water in well, and then water the new seedlings every day until well established.


FEEDING — When the new spring growth reaches 2″ high, a balanced fertilizer of 12-12-12 should be applied. Another method of feeding is to combine two tablespoons of Ammonium Sulfate mixed with a cup of bonemeal, and lightly scratching it in. This would be sufficient for each plant. Water in if there is no rain. Nitrogen promotes growth in roots, foliage and stems; phosphates promotes root growth and hardness of stems; potash promotes intensity of color. All three are essential. It is very important to attend to slugs and snails by baiting or picking them.

THINNING — It is essential that each delphinium plant be properly thinned each year. Newly planted, first year seedlings should have only one flower spike. Second year delphiniums should only be permitted to have three flower spikes. Older and established delphiniums should be permitted to have only five flower spikes. When the new spring growth is two-to-three inches high, select the correct number of the strongest shoots to remain, plus an extra one in case of snail or animal damage, and cut off all other shoots at ground level. The one extra shoot should be cut off when you stake the plants. A properly grown 8-year-old delphinium can have as many as twenty to fifty shoots in early spring. If all were permitted to grow on, the plant would literally bloom itself to death. Thinning is essential.

STAKING — The correct method of staking garden delphiniums is to contain the stems of the plant, not the flower spike. When the thinned delphs are 9″ to 12″ high, four dark green, thin bamboo canes are inserted into the ground, forming a square around the plant. The canes should be four feet tall. The first tie should be tied tightly to the canes, 10 to 12 inches up from the ground. The second tie should be tied 24 inches up from the ground, and situated just below the first bottom floret and tied a bit looser than the fist tie. This method of staking permits the heavy flower spikes to move within the confides of the twine without breaking. If the flower spike is tied to the stake, it will break at the base of the tie. If staked correctly, the twine and the stakes will not be obvious. Also, any staking should never be higher than the flowering spikes for it will ruin the graceful beauty of the delphinium.

WATERING AND MULCHING — Delphiniums should never be permitted to dry out, before or after flowering. Water may be applied by an overhead sprinkler up until the florets are in bloom. Mulching conserves moisture but certain kinds of mulch are safe havens for slugs and snails that equate the delphinium to a five-star restaurant. Mushroom compost is a good mulch and so is well-rotted manure, but for those manures that contain weed seeds, keep pulling the weeds as they emerge.

AFTER FLOWERING — Cut off the spikes under the first bottom floret on the spike and allow the green stems and the foliage to die down naturally. When they are entirely brown, cut them off at ground level and the new growth of a second bloom will be about 12 inches high. If you cut down the entire spike to the ground afer it has bloomed and when it is still green, you’ll force the delphinium into an immediate second growth when the crown does not have sufficient energy, which will shorten the life of the delphinium.


When the delphiniums die down and become dormant, cut down all stems and foliage to ground level, and remove all leaves, debris, stakes, and weeds around the crowns. This will eliminate hiding places where pests may overwinter. In areas of the country that have unusually heavy infestations of slugs and snails, late winter and early spring can be times of excessive amount of damage. Covering the tops of the crowns with coarse gritty sand helps to deter the pests. A solution of 2 oz. of Aluminum Sulphate mixed in one gallon of water, enough for four delphiniums, when poured around each dormant crown, will kill all slugs and snails, as well as their eggs, as a result of its astringent action. Overuse of this solution will also result in extremely acid soils, so care should be taken.

Delphiniums are hardy perennials and grow in all zones that have a cold winter dormancy. In areas that have no cold winter dormancy, they are grown as biennials, blooming 2 or 3 times in one season and then exhausting themselves.


The primary pests of the delphinium are slugs and snails. Slug Pubs work to a certain degree, but they are messy and many are needed to be effective. Slug pellets containing metaldehyde scattered about may work, but slugs do recover from metaldehyde, especially in wet weather. Slug pellets based on methiocarb are more effective, but care should be taken because both types of pellets are poisonous to animals. A sprinkling of red cayenne pepper deters slugs, snails and rabbits from eating the young new top growth in the spring, but it must be reapplied after each rain.

The Pulsia, the Tortrix and the Angleshade moth caterpillars can damage the embryo flower buds before they emerge. A rolled up leaf at the top of the stem is a telltale sign of this caterpillar. Handpicking off the ½ inch culprits, along with careful observation, certainly will help. With large numbers of delphiniums, a spray will be necessary. It is wise to remove all staking canes over winter because the hollow stems of the bamboo canes can be a perfect place for pests to hide.

Waterlogged soils in winter will cause the crown to rot and that is why excellent drainage is absolutely necessary. Also, any damage done to the crown by a slug or snail, by a hoe, or even by a stem that has broken off below ground level, could cause water to enter the crown and cause it to rot over winter. It is also thought that repeatedly heavy applications of nitrogen may add to crown rot. Plant breeders and exhibitors consider it good practice to spray their delphiniums with a good systemic fungicide in early June. This controls any possible crown rot on older crowns, whether or not any cuttings have been taken for propagation.

The only life threatening virus disease is the Cucumber Mosaic virus. This virus is rare and does not spread widely; out of 1000 plants, there might be one with CM. The only solution is to destroy the entire plant. Mildew may cause problems late in the summer after flowering, in areas that have high humidity and high night temperatures, but it is easily remedied and does not effect plants that have not been neglected. Black spot may be present, but it is easily treated with a fungicide, especially if it is done early.

© 1998 Log House Plants