How to Raise Dahlias Successfully (1921)

This article is adapted from a dahlia catalog published in 1921 by The Somerhousen Dahlia Gardens in Chestnut Hill, Pennsylvania. 

Although the original work is in the public domain, this article has been edited for the modern reader and may contain new material. 

This version is Copyright © 2024 by Steve K. Lloyd and may not be reproduced without permission.

The Somerhousen Dahlia Gardens

1921 Catalogue of Dahlias

A.M. Buckenham, Proprietor

Edited with revisions by Steve K. Lloyd © 2024

When you receive your dahlia tubers, do not put them in some out-of-the-way place to dry out and die. Unpack them and lay the tubers flat on their sides in a box of damp earth, taking care to see that the sprout or eye is turned up. Do not use wet or sticky soil. Use soil that is damp enough to crumble nicely. Cover the tubers with three or four inches of this soil and set them in a cool place until planting time.

This varies somewhat with the locality, as well as with the time you wish the dahlias to bloom. In the Middle Atlantic section of this country, planting can be done from May 1st to June 15th for the average crop of flowers. Further south planting can be done in February and March. 

In the New England States, where the season may be short, planting can be made after the danger of frost is past. Nothing is gained by planting too early. It is best to wait until the ground becomes thoroughly warmed, and is in good working condition. If planted too early, when the ground is cold and damp, the tubers may rot. 

Dahlias bloom from eight to ten weeks after planting. This fact is often of value in deciding when to plant and when the flowers are desired. Some of the finest exhibition blooms are obtained from planting as late as the 1st of July.

An open sunny place is the best location for the great majority of dahlias. Except in a few instances they do not succeed in heavily shaded spots. 

Some of the more delicate varieties do better in partial shade, especially during the hotter portion of the day. Some of the finest exhibition flowers can be produced only in partial shade, which protects their delicate coloring from the fading action of the sun. If too much shade, the plants run to long stalks and foliage with few or no flowers. In the sun they form stocky, well-developed plants.

They are the better for some protection from sweeping winds which are likely to come after they have made their growth. Planted along a wall, fence or arbor, and among shrubbery, they are not so apt to become broken by the wind and storm and the plants are not likely to become lopsided and unshapely.

It is well to remember that dahlias are large plants, requiring plenty of space for their best development. At least three feet or more apart, where the space is available, is ideal. Where space is limited they can be crowded down to two and a half to two feet apart, but the closer they are planted the smaller will be their growth. Where they are planted singly and irregularly, three feet is sufficient; in a garden row or along a fence where the row is single they may be crowded to two feet apart and still do well. Such plants should not have the center shoot pinched, but should be allowed to grow on to a single stem, which will need stalking.

For those who wish to plant dahlias in a plot or field (and this is the right way to do it if space permits) we recommend planting in rows four feet apart and the plants two feet apart in the rows. This can be done quite easily by running furrows six inches deep with a hand cultivator plow and dropping the tubers, sprout up, the proper distances apart along the rows; then cover up carefully to protect the sprouts and when the latter have come up so that two sets of leaves have developed, then pinch out the sprout above the second set of leaves. This gives a bush of four branches, which will form a short, self-supporting, stocky plant. 

Pinching delays flowering about two weeks, a fact worth remembering, especially for those who have a short season. The plants should be cultivated between the rows and treated otherwise as for dahlias in general.

Commercial growers usually prepare the ground as in the preceding and plant the tubers ten to fifteen inches apart. The plants are not pinched, and they support each other by their mass effect in the rows.

Dahlias do well on a great variety of soils. A light, well-drained sandy loam is best suited to their needs, but they will grow and do well in clay loam, sand and even in ashes. The large tubers require a great deal of moisture, but wet soil is fatal to them, so that good drainage becomes essential. If the soil is heavy, it may be made suitable by the addition of sand, leaf mold or ashes, well spaded in and incorporated so as to break up the clay and make it porous. A certain amount of vegetable matter derived either from well-rotted manure or leaf mold is helpful in furnishing humus which aids in retaining soil moisture in dry weather.

The soil should not be prepared until it is in good working condition, that is when it is mellow and crumbles when dug and does not cling to the spade or fork. Never plant in wet, pasty soil, such as clings to the fork or spade. The soil should be finely pulverized and is then in the proper condition for receiving the tubers. The soil should be dug to a depth of twelve or fifteen inches.

While many growers prefer to add manure as a fertilizer when planting, it is not essential; it may even prove detrimental in producing too rank growth of the plants and consequent paucity of flowers. The proper time to fertilize is after the growth has been attained and the flower buds begin to appear. Fresh manure in contact with the tubers when planted may cause them to rot and prove fatal, therefore avoid its use.

The tubers should be planted from five to six inches below the surface of the soil. This puts them down in the moist layers of the soil and prevents them from drying out and becoming stunted during the hot, dry weather of midsummer. Dahlias are great lovers of moisture, and this can only be constantly maintained at this depth.

Lay the tuber flat on its side, that is, with the long axis horizontal. Never stand a tuber upright or on end, as the new roots are given out from the junction of the sprout with the tuber, and if these are not well covered and in a constantly moist situation, they will fail to develop the large roots which eventually become tubers, or as some people prefer to call them, potatoes. Dahlia tubers, while they are not potatoes, require much the same conditions for development as do potatoes.

In planting see that the eye or sprout is turned upwards, so that it can grow without hindrance. The eye can be found on the crown end of the tuber. The crown end is the portion where the tuber joined the stalk of the old plant from which it was taken. When you have laid the tuber on its side, sprout up, and five or six inches deep in the ground, cover with finely pulverized soil, filling the hole up even with the surface, pressing carefully so as not to break the sprout. If conditions are favorable the sprout will grow rapidly and appear above ground in from ten days to two weeks.

Cultivation. 

As soon as the sprouts have grown two or three inches above the ground it is time to cultivate. Hoe the surface of the ground and keep free from weeds. This should be done often and the surface should never be allowed to form a crust. Never cultivate when the ground is wet. The day following a rain is usually the best time. Cultivate deep (two or three inches), and continue until the plants begin to bloom; then stop, as cultivation will now do harm. Breaking the surface of the soil prevents the rapid evaporation of moisture from the soil and allows the plants to take it up.

Supporting the Plants. 

When the plant has attained the height of twelve to fifteen’ Inches a stake five feet long and tapering to a point at the lower end should be securely driven into the ground at a distance of three or four inches from the plant, and the plant tied to it. From time to time as growth continues, the upper portion of the stem and branches should be secured. In this way the plants will remain upright and the large, heavy branches prevented from breaking off from their own weight by the winds. Use strips of muslin. An old sheet torn into strips of an inch in width makes a most satisfactory tying material. Soft hemp twine will answer, but small twine and string usually cut and injure the stalks.

Proper Time to Use Fertilizer. 

When the buds begin to form, then begin fertilization. The plant has now made the major portion of its growth and fertilizer will do no harm. If fertilized early the plants are apt to become rank, all stems and foliage, and too tall. Old, well-rotted cow manure worked into the soil is best. Usually it is not obtainable, and in its stead pulverized sheep manure may be used. Pure bone meal and acid phosphate, equal quantities of leaves will push ahead and produce buds. Of these all but the terminal bud should be removed. On the above principle, disbudding should be practiced, as it gives larger and more perfect flowers. For the finest large exhibition blooms disbudding should be done along the entire length of branch or stem; fewer flowers will be the result, but their quality will more than compensate for the loss in numbers.

Watering. 

As a general rule, dahlias should not be watered unless the ground is very dry, or during long periods of drought. If you water them, give plenty so that it goes- deep. Frequent sprinkling of the sur-, face does more harm than good, for it brings the roots near the surface, where they are apt to suffer from their inability to get a constant supply of moisture, such as they get when they are deeper down in the soil.

The dahlia is, generally speaking, rather free from enemies, but at times an occasional plant is attacked in one of several ways. We have found the cut-worm and the stalk-borer to give us most trouble.

The cut-worm often attacks the young shoot just as it emerges from the ground. Usually if the sprout is healthy and vigorous, secondary shoots come up a little later, or other sprouts from the crown may start. Later on when the flower buds are opening the worm may attack the flowers and destroy them. When they do, they do it quickly and leave little behind. At that time the best method of attack is to use a flashlight after dark and examine each plant carefully and the worm is usually easy to find. This method offers the surest possibilities for destroying them. At times attacks on the plants from cut-worms may be prevented by making a poisoned bran mash and sprinkling or making a ring of it around the plant.

In wet seasons the slugs are troublesome in ascending the stems and rapidly devouring the foliage and flowers and causing great havoc, usually choosing the finest specimens, as though from malice aforethought. Handpicking and close watching will usually give the best results. A dry ring of powdered lime around the plant will suffice to keep them away as long as the lime remains a dry powder.

The stalk-borer is the larva of an insect which deposits its eggs in the fall at the base of the stems of old weeds and grasses. In May the larvae hatch and crawl to nearby thick-stemmed plants, such as the tomato, com, dahlia and others, and by boring a hole, enter them, and as the larva develops it feeds on the inside soft tissues of the stem. In time, so much of the supporting structure is removed as to retard the growth and the top weakens and falls over. This condition is readily recognized by the stunted appearance of the plant, which up to that time has been growing rapidly, as the plants are apt to do in the early stage of their growth. 

By closely examining the stem of the plant in such cases there will be found a hole in the stem, through which the excrementa is passed, and sometimes another hole several inches above it. A drop of carbon bisulphide or, better still, of turpentine introduced through a slit made in the upper portion of the plant will cause the larva to leave the stalk and never come back. Such treatment is usually satisfactory if the condition is discovered in the very early stage, but is not satisfactory when much damage has already been done. In the latter case it will be found the most satisfactory thing to cut the top of the plant off in the sound tissue below the point of injury, looking to laterals to push out from the axils of the leaves. Always kill the larva when possible.

Should the aphis attack the stems, the various nicotine preparations may be used with prompt results. In case caterpillars or other leaf chewers attack the plants the arsenate of lead spray works well. For mildew, a solution of Bordeaux Mixture may be used.

As soon as the frost has cut the tops of the dahlias, the sap recedes into the roots. Two or three days after a heavy, killing frost is the best time to dig the roots. Cut the stalks back to within two or three inches from the crown. In digging use a spade, fork or long-handled shovel, and dig wide of the plant, say fifteen to eighteen inches, to avoid cutting off the tubers. Some varieties have very long necks and tubers, while others have short ones. By digging wide you take no risks.

Do not pull the clumps up out of the ground, but dig deep and lift the soil and the tubers as you go round the plant. This enables you to get the clumps out without breaking the necks, which does so much harm to the dahlias. A tuber with a broken neck is usually no good. The young dahlia plant grows from a sprout on the crown, which is that part of the lower end of the old plant where the tubers join the stem. In order that a tuber may grow it must have direct connection with the sprout on the crown by means of an unbroken neck. This explains the failure of dahlias to grow in many instances. 

A clear, sunny day is ideal for digging dahlias, and when you have lifted the clumps allow them to stand in the sun for two or three hours, after which any excess soil may be removed and they are then ready for their permanent storing place.

The best place to store dahlias is a good, cool cellar, such as will keep potatoes well, and where the temperature remains fairly constant at from forty to forty-five degrees, and the air is neither too damp nor too dry. Stored dahlias are so apt to suffer from the latter. Cellars with heaters and cement floors are usually too dry and the roots shrivel up. To a certain extent this may be prevented by lining barrels or boxes with a good, heavy thickness of paper and thus excluding the drying air.

In all cases pack the clumps one on top of the other, each clump upside down for drainage. In the stem of the dahlia is a strong, rank, acrid juice, which if allowed to settle back into the crown may cause the whole clump to rot. Turning upside down allows this juice to drain out, and is favorable to the preservation of the crown. In case you have labeled your varieties, always tie the label around the neck of one of the tubers to make sure that it will not come off and get mixed with others. If the label is tied around the stem, above the crown, as the stem dries and shrivels it becomes loose and is apt to fall off when the clump is turned upside down.

In case the temperature and moisture conditions have been all right, your roots will need no further attention until spring, when planting time arrives.

It is well, however, to look at the roots every three or four weeks, especially if the cellar is dry, and an occasional sprinkling with water and. covering with several thicknesses of an old carpet or bags will prevent them becoming dead dry, and carry them through until spring.

About a week before planting time, look over your clumps and divide them into single tubers, having at least one good, visible sprout on the attached portion of the crown. Never plant a whole dahlia clump; the results will be little short of failure. Each tuber with its neck and piece of crown containing at least one eye will give the best and strongest plant that it is possible to get from a dahlia. The size of a tuber has very little to do with the results; small tubers are as good as large ones, and sometimes much better; some of the finest varieties have poor roots at best and their tubers usually come through the winter in a more or less shriveled condition in spite of our efforts.

This is quite interesting, as no one can be certain what a seed will produce. All the best new varieties have been raised in this way. Some growers may get one or two good new varieties out of several thousand seedling plants, while one or two good things may appear among a hundred or more; the uncertainty of the results lends a fascination to this method of raising dahlias.

The seeds should be planted in boxes of good, rich, well-prepared soil in March, either in house or greenhouse. In six to ten days the plants will appear. When these have made two sets of leaves, each plant should be pricked off singly into 1½ inch pots. They do best in a cool house rather than a warm one, and should be shifted into larger size pots as they become crowded in their growth. After May lOth they can be planted out in their permanent positions, and treated in all respects like dahlias grown from tubers.

This class is characterized by full, double flowers having long, narrow, incurved or twisted petals, with sharp, divided or fluted points, and with revolute margins, forming a more or less perfect tube. Their effect is devoid of stiffness or formality, and they constitute one of the most fascinating and popular types of the dahlia, as shown on the cover of this catalog

This class is intermediate between the cactus and the show dahlia. Flowers are large, full to the center, with broad, flat, incurved or reflexed petals, giving an irregular formation devoid of stiffness and formality. They are all strong, vigorous growers, early and free bloomers.

This class had its origin in Holland and was named on account of its resemblance to the Japanese Paeony. Flowers large, on long stems, and have conspicuous open centers around which the large, broad, gracefully curled and twisted petals are rather loosely and irregularly arranged. They are devoid of stiffness and formality, and are sometimes referred to as the “Art Dahlias.”

This class is a branch of the ball type. The flowers are round, symmetrical and perfectly formed, the petals being regular, cupped or quilled and usually full to the center. They are early, free and continuous bloomers; the dahlias of our grandmother’s gardens.

This class is an improvement on the old-fashioned single dahlia. Center is always visible and surrounded by one or two rows of large petals, which are more or less symmetrically arranged.

This type is of French origin, and the flowers are medium to large in size with open centers and one or more rows of petals. At the base of the petals and surrounding the center a ring of small modified petals gives the collarette. The collarette is of a different color from that of the petals, and the contrasts are quite pleasing.

This class is a miniature form of the show dahlia, having the same round, ball-like form, but much smaller in size, ranging from an inch and a half to two inches in diameter. The plants are dwarf (twelve to eighteen inches in height), of branching habit and produce a profusion of flowers that is truly astonishing, filling the demand for cut flowers.