Abstract

This is a discussion of three methods of propagation of the genus Dianthus for the home gardener. All Dianthus may be cultivated by these methods, but greenhouse propagation will not be included to narrow the subject.

Introduction

The genus Dianthus is a group of plants belonging to the family Caryophyllaceae. They are commonly known as pinks and carnations. The plants are annual, biennial or perennial in growth. They are not true herbaceous plants as there are no over-wintering structures underground. Rather, there is a single woody stem with herbaceous branches (Bird, 1994). The leaves are narrow and parallel and are found as pairs on nodes at right angles to each other on the stem. Leaf color ranges from bright green to blue-gray and often with a glaucous bloom. The plants are either mound-forming or spreading in habit. Height ranges from two inches to approximately forty inches.

Identifying characteristics consist of monoecious flowers with two or three styles and ten stamens (Bird, 1994). The flower itself has five petals which are flattened and may be found as a solitary flower or as a dense clustered flower head. The color of the petals range from white, to tints and shades of red, with yellow being a rare exception. The flowers themselves may be deeply fragrant. The derivation of the word "Pink" is unknown but does not refer to the color of the flower. To shed a little light on the origin of the name "Pink", the herbalist John Gerard wrote in the year 1597 of "faire double purple flowers of a sweete and spicie smell, consisting of five leaves, sometimes more, cut or deeply jagged on the edges, resembling a feather; whereupon I gave it the name Plumarius, or feathered pink" Gerard(1597, cited in Bailey, 1938).

Reproductively, most Dianthus are primarily self-sterile. In other words, they require pollen from another plant for fertilization (Bird, 1994). Insects are the primary pollinators, and in nature, species Dianthus often cross with each other.

Methods of Propagation

Propagation by Seed

Propagation of Dianthus by seed is an efficient, economical method of propagation, but seed propagation is not a guarantee of genetic uniformity of succeeding generations. However, the genetic diversity of the seeds does allow for selection of wanted traits for the breeding of new cultivars. It is also an easy method. No pretreatment is needed except for D. glacialis (unspotted) which needs a period of cold stratification (Lloyd and Rice, 1994).

Dianthus seeds should be harvested when fresh. Sophie Hughes (1991) indicates that seed pods become "straw-like in texture, curling their tips upwards and outwards to reveal black seeds which rattle within the dry husks". They may be directly shaken into a labeled envelope and placed in a warm, dry place.. If not sown immediately, they should be stored in a cool, dark place such as the refrigerator. The seeds are a little brittle around the edges so care must be taken in their handling.

Germination occurs in five to ten days, but may take up to four weeks. Studies by Norman C Deno (1993) have concluded that twenty species of Dianthus achieved 70-100% germination at 70 degrees F. Deno (1993) has written, "The species in which both fresh and DS(dry storage) seed were studied were D. barbatus, deltoides, nardiformis, plumarius, and stenocalyx. The species in which only DS seed was studied were D. alpinus, broteri, crinitus, darwasica, erinaceus, fragrans, frigidus, glacialis, haematocalyx, leptopetalus, myrtinervis, neglectus, pancici, repens, and seguieri." Dianthus arenarius was shown to be an exception in his studies in that light was a requirement for germination. It is also possible that some seeds may require light when fresh for germination, but after storage in a dry place, light is not needed. Such is the case with D. superbus alba (Deno, 1996).

Almost any medium may be successfully used for the germination of Dianthus, but several peat-based, soilless mixes such as Sunshine Mix #2 (no base fertilizers) and Jiffy Mix do the best job. For example, Jiffy Mix is composed of 50% sphagnum peat and 50% vermiculite. The medium should be moist before planting. This may take a little work because of the quantity of peat in the mix, but warm water will hasten the process. Seeds should be sown thinly, covered lightly, and kept moist. Bottom heat should be applied under the flat to provide a ten degree temperature gradient between the soil and air temperatures. A weak solution of fertilizer may be applied after rooting has occurred. One-quarter to one-half the recommended strength may be applied on a weekly basis.

Seedlings should be transplanted to a deeper soilless mix at any point from the one true leaf stage and upwards in size. Dianthus are very forgiving of transplantation , but better growth may be achieved when transplanted at an earlier stage. For best growth, plants should be removed from bottom heat and kept at daytime temperatures in the low 60’s; nighttime at 50 degrees F (Crockett, 1961). Bright sunshine or a fluorescent light unit provides an adequate light source for the plants. An ordinary shop light with one warm white and one cool white lamp works well. Transplantation to a garden site may be done when roots are well developed, and when there is no danger of frost.

Propagation by Cuttings

Propagation by cuttings ensure that the succeeding generation will have the same genetic characteristics as the mother plant. It is a way of perpetuating the preferred plants in the garden with little cost to the propagator . It is a relatively simple process, but must be done at the correct time. Late June and early July, after flowering, is the best time for cutting propagation, but cuttings may be taken into September (Bird, 1994).

In general, flowers should be deadheaded to encourage lateral growth and prevent the loss of energy of the plant by not allowing it to set seed. Lateral shoots, according to John D. Mapel (1993), make excellent cuttings. More specifically, cuttings from Allwoodii-type hybrid pinks (modern pinks) should be taken from nonflowering shoots and shoots which have not started to lengthen for flowering (Hughes, 1991).

For best results, it is recommended that cuttings be taken on an overcast day from healthy one-year old plants (Hughes, 1991), that is plants that have bloomed for two seasons. They should not be taken from woody sections of the stem. If the plant appears to be dry, it should be well-watered the day before the cuttings are taken. A cut should be made about one-quarter of an inch below a node at a 45 degree angle. It should include four or five pairs of leaves, and the pair nearest the cut should be stripped off carefully before propagating (Mapel, 1993). Before each cut, it is recommended that the knife be dipped into a solution of one part bleach to nine parts water to prevent the spread of disease. Cuttings from each plant should be placed in a plastic bag with a label until they are put in a rooting medium. This bag should not be left in the hot sun and may be stored in the refrigerator for a short time.

To root the cuttings, use a well drained, moist medium such a 50/50 mixture of perlite and vermiculite or a combination of one part peat to two parts perlite (Dube, 1993). Almost any medium may be used including sharp sand (do not use beach sand). The stem of the cutting should be moistened with water, dipped into rooting hormone (active ingredient 0.1% IBA), and placed in the rooting medium. Use a pencil to make a hole rather than just sticking the cutting directly into it. This allows most of a powdered growth hormone to stay on the stem. It also prevents diseases from entering small abrasions that may occur when forcing the stem into the medium

(primarily a concern with sand). The pot should be bottom-watered, covered with a plastic bag, and placed in a well lit area out of direct sunlight until rooting takes place. Once or twice a week, the bag should be opened and checked for moisture content. The rooting medium should be kept moist, but not too wet. Rooting takes place in approximately three to four weeks, but may take as long as three months (Dube, 1993).

Once the plant begins to root, new growth will appear from the central leaf rossette (Hughes, 1991). At this point, the bag should be opened gradually over a period of a couple of days to allow fresh air to enter. This also prepares the plant to acclimate to the outside environment.

Certain Dianthus types may benefit from pinching at this stage of growth to encourage bushy plants. Correct pinching of a plant is done when part of the main stem, the growing point, is removed.

There is some discrepancy as to what plants to pinch and what not to pinch. In her book Carnations and Pinks, Sophie Hughes (1991) includes old pinks, laced pinks, and modern border pinks as types of Dianthus that demand pinching for the health of the plant. She feels that if this is not done, the stems will elongate, and there will be meager flowering. On the other hand, John Galbally (1997), in his book Carnations and Pinks for Garden and Greenhouse, feels that the only Dianthus that should be pinched are the modern repeat flowering types. The old pinks which do not rebloom should not be pinched. If this is done, flowers will not be produced that summer. According to Mr. Galbally (1997), the only time that a border carnation should be pinched is when it sends up only one flowering stem without sideshoots. Pinching , as stated by Mr. Galbally, would "induce sideshoots for propagation and thereby rescue the plant from extinction".

Most propagators of Dianthus cuttings pot the newly rooted plants into pots for wintering-over in coldframe or greenhouse. If facilities are a problem, planting outdoors in a well drained flower bed works very well. Plants should not be mulched with leaves but rather marsh hay or evergreen boughs to catch the snow. To prevent crown rot, the mulch should be removed as soon as possible in spring. Dianthus do not like wet feet!

Ground Layering

In the garden, two categories within the genus Dianthus may be propagated by ground layering: pinks and border carnations. Ground layering is rarely used for pinks due to the difficulty in preparing sideshoots. Stems are just too narrow to slit with a knife (Galbally, 1997), and even if there is success, keeping the prepared sideshoot from drying out during rooting may be difficult. Similar results may be obtained by cutting propagation which is simpler. On the other hand, layering is one of the principle methods of propagating border carnations (Hughes, 1991). The procedure is to choose a healthy, well watered plant which will have at least four healthy shoots. This should be done in midsummer to early autumn, after flowering, on plants which are one to two years of age.

The soil, adjacent to the plant, should be loosened to a depth of about three inches. Equal parts of sand and moist peat should be added so that each component, including the soil On the other hand, layering is one of the principle methods of propagating border carnations (Hughes, 1991). The procedure is to choose a healthy, well watered plant which will have at least four healthy shoots. This should be done in midsummer to early autumn, after flowering, on plants which are one to two years of age.

The soil, adjacent to the plant, should be loosened to a depth of about three inches. Equal parts of sand and moist peat should be added so that each component, including the soilThe shoot is then pushed down, with the tongue open, into the prepared soil. Care must be taken when this is done so as not to break off the shoot. By pushing down on the internode area to position the stem, there will be less chance of breaking off the shoot. At this point, a heavy duty pin can be pushed over the shoot and down into the soil to ensure that the shoot does not come out of the soil mixture. The soil should stay moist for approximately six weeks or until rooting occurs. After rooting, the young plantlet may be left attached to the mother plant until it is relocated to a new flowering position (Galbally, 1997).

Conclusion

All three methods of Dianthus propagation have advantages and disadvantages. In the future, there is much work that may be accomplished by hybridization within the Dianthus genus. Hybridization may be accomplished by any gardener with an interest in the flowers in their own gardens. In cold climate gardening, zones 2-4, winter hardiness is a key aspect in consideration of the propagation of new cultivars. The American Dianthus Society is an excellent source of knowledge in every aspect of growing and propagating this genus. Books on plant propagation and breeding are also helpful in methods of hybridization.
 
 

Bailey, L.H. 1938. The garden of pinks. The MacMillan Company, New York.

Bird, R. 1994. Border pinks. Timber Press, Inc., Portland, Oregon.

Crockett, J.U. 1961. Greenhouse gardening as a hobby. Doubleday & Company, Inc., Garden City, New York.

Deno, N.C. 1993. Summary of data arranged by genera p.132 in Seed germination theory and practice, 2nd Ed., Published by the author, State College, Pennsylvania.

Deno, N.C. 1996. Data in alphabetical order according to genera p.38 in First supplement to the second edition of seed germination theory and practice, 1st Ed., Published by the author, State College, Pennsylvania.

Dube, M. and J.D.Mapel. 1993. Starting the Dianthus from cuttings. The Gilliflower Times 2(4):1-3.

Galbally, J. with E. Galbally. 1997. Carnations and pinks for garden and greenhouse. Timber Press, Inc., Portland, Oregon.

Hughes, S. 1991. Carnations and pinks. The Crowood Press Ltd, Ramsbury, Marlborough, Wiltshire, Great Britian.

Lloyd, C. and G. Rice. 1994. Garden flowers from seed. Timber Press, Inc., Portland, Oregon.

Smith, F.C. 1990. A plantsman’s guide to carnations and pinks. Ward Lock Limited, London, England.