PROPAGATING HERBACEOUS PERENNIALS IS IT REALLY THAT MYSTERIOUS? David J
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PROPAGATING HERBACEOUS PERENNIALS IS IT REALLY THAT MYSTERIOUS? David J. Beattie, Department of Horticulture, Penn State University Introduction instance, Heucheramicrantha 'Palace Purple' is prized for its rich, bronzefoliage. It iseasily propagated byseedand The use of herbaceous perennials continues to be one of does notrequirestratification. Eventhough it has a cultivar thefastestgrowing segmentsofornamental horticulture, namethatimpliesuniformity, greenoroff-colorvariantsare but much mystery still surrounds their propagation and regularly produced and must be rouged out. If this is not culture. Although the basic principles of propagating done rigorously, manyofftypes enterthe market. Forthe herbaceous perennials are similarto woody plants, many mostdesirable plantsthough, selectionsshould be madeof of the specific practiceshave been proprietary; thatis, the the besttypesand theyshould beasexuallypropagated. In methods have resided in the experience of a few master contrast, Campanula carpatica 'White Clips' is alsopropa propagatorswhoseinformation has been passedfrom one gated by seed, but the populations are very uniform, so generation tothe next. In addition, since many perennial there is no practical reason to propagate it asexually. nurseries haveseveralthousand taxa, it is understandable thattheexactpropagation methodsfor manytaxa maynot Someperennial seed, especiallythose in the peafamily like be well known. However, with more perennials being Baptisiaaustralis, have hard-coated seedsthat, when dry, grown, there is less mysterysurroundingthe propagation do not allowwatertoeasilyenterthroughthe seedcoatto of these popular garden plants and the information is begin initiating the germination process. Baptisia seed generally more available. germinateseasilyifit is sownwhentheseed is fully ripe, but before it is allowed to dry out. If the seed dries out, seed Herbaceous perennials grown above ground during the coats must be broken down in a process called scarifica growing season, but with the onset of short days and tion. This is accomplished byeitherrubbingthe seed lightly freezing weatherthetops die, and the plant retreats to an betweentwo layersofsandpaperor by immersing theseed underground storage organ. These storage organs as for 15 minutes in concentrated sulfuric acid. Usually no sume many sizes, shapes, and names. They may be further treatment, such as stratification is necessary. fibrous rooted structures, bulbs, tuberous roots, tubers, rhizomes, stolons, crowns, orpips, andfunction as reser The perennial industry has experienced rapid growth in the voirs ofgrowth regulators, water, and nutrientsthat propel lastfew years, resulting in customerswho no longerwant the plantsinto growththefollowing season. Thesestorage common seed-propagated plants like Shastadaisy, butare units can be lifted, stored, shipped, and can serve as the looking for named cultivars. The resultis that, while seed basic propagating units. propagation willalways beimportant, greateremphasis will be placed on asexual methods to propagate the new My objective is to discuss some of the principles and cultivars. practices of propagating herbaceous perennials, concen trating on rootcuttings and division. Only one important SHOOT TIP CUTTINGS: Many popular genera of peren genus is propagated bygrafting; seedand shoottip propa nials like Artemisia, Dianthus, Coreopsis, Lavendula, and gation will be lightly covered, and tissue culture propaga Delphinium can be propagated by shoottip cuttings. The tion has been, and will be, adequately covered by other principles and methods are similar to those for woody speakers. plants. One significantdifferencefrom woodycuttingsis thatlittle orno rooting hormone is necessary. If it is used, SEED: The majority - perhaps more that 50% - of all it is usually the equivalent of Hormodine #1 (1000 ppm herbaceous perennials are propagated by seed. Seed IBA). Anotherdifference is that perennial cuttings, since propagation has both advantagesanddisadvantages. The they are soft, non-woody tissue, are more susceptibleto seed is a relatively inexpensive propagation unit, easily rotting in the propagation bench. This is easily overcome stored, and is well adapted tothe automation provided by either by reducing the misting frequency, or by covering the seeding machines. Forthis reason propagating perennials plants with rowcovermaterial. Thiscoveris a thin, white, is becoming increasingly popularfor bedding plantgrow light-weightfabric. Itis routinely used by European grow ers. Since herbaceous perennial seeds generally do not ers who prefer covering freshly-stuck herbaceous cuttings have as long or as deep of dormancy as do woody seeds; with thisfabric to placing them in a mist bed. stratificationtimesare usually shorter. However, seedsof someperennialstendto beshorter lived than their woody Cuttings of herbaceous perennials are of two types. The counterparts, and the biggest problem facing perennials mostcommon is thetip cutting which is taken atthetip of propagators is the industry-wide problem oflocating high elongated growth as is done with a woody shrub. Aster, quality, true-to-nameseed. Chrysanthemum (Dendranthemum) and Tricyrtis can be propagated bythis type of cutting. Incontrast, thegrowth Seed propagation has several disadvantages. Seed propa habit of other plants WkeArmeria, Geranium and Achilleado gated plants may have many different phentotypes. For not provide an elongated, well-defined cutting. Here the Georgia Commercial Rower Growers Association Newsletter • January - February, 1994 • Page 16 cutting must be taken early in the growth cycle when the pack flats. The flats are then placed in a high humidity shootis short, often with several attached roots. This type chamber in a shaded portion of a 60°Fgreenhouse where of cutting, sometimes referred to as a "rooted cutting," often they can be observed for rooting. As each cutting or group requires minimal misting and establishes quickly. of cuttings develop shoots and begin to root, they are removed and transplanted. In the second method, the The second type of herbaceous perennial cuttings is rep cuttings are packed in rows into a 3 to 4" deepflat. Theflat resented by easy-to-root plants likePhysostegia, Chelone, is placed on the bench at a 45 degree angle, and alternate Monarda, and many mints which can be rooted by leaf- layers ofcuttings and medium are placed each on top of the node cuttings. The entire stem can be sectioned into other until theflat is filled. Flatsfilled in this mannercan hold individual nodes, each with one or two leaves. Although 300to 400 cuttings, depending on the root diameter. smaller than shoot tip cuttings, their increased numbers represent a way of inexpensively and rapidly increasing While the polarity of a shoot cutting is very important, it is less so with root cuttings. Even though fastest shooting plant populations. and rooting is obtained ifcuttings are oriented inthe upright, ROOT CUTTINGS: Root cuttings are a very useful proximal (with the end that was closest to the soil like method of asexual propagation, particularly for plants that position, cuttings placed in a horizontal position appear to do not produce many seeds, and have growth habits that root equally well, but require more space. produce relativelyfew divisions or cuttings. Manyplants in the Borage family like Pulmonaria, Brunnera, Anchusa, Not all plants can be propagated by root cuttings, nor is it and Mertensia have these characteristics and are routinely desirable to propagate some plants by this method. For propagated by root cuttings. This method can be efficient, instance, variegated plants like Brunnera macrophylla too. Byusing a combination of root cuttings and division, Hadspen Cream' or 'Alba' can only be propagated by I have propagated nearly 100 salable-sized Pulmonaria division. When propagated by root cuttings, plants with 'E.B. Anderson' plants from three root pieces that were green leaves result. This is because the origin of the shoot approximately 10 inches long. Imaginewhat a root-bound, within the root tissue is different from the tissue that two-gallon Pulmonaria would yield! Root cuttings are resulted in the variegation. usually thought to be only for plants with thick roots like Acanthus mollis, but thin-rooted perennials like Phlox DIVISION: Division is one of the simplest and easiest paniculata, summer phlox, willingly form shoots on root methods of propagate perennials like Astilbe, Hosta, cuttings also. Hemerocallis, Iris, and Paeonia. With this method, the storage organ is divided into sections, usually, but not Cuttings are usually gathered while the plants are dormant from Novemberto February. There are exceptions. Papaver orientate, the oriental poppy, goes dormant in August, so cuttings can be taken anytime thereafter. Anenome sylvestrisforms shoots on roots still attached to the plant, so they can be excised anytime after late September and transplanted. Cuttings can be gathered from plants that are GardenSmith grown in the field, but are most easily gathered from container-grown stock plants. Container-grown plants Greenhouse & Nursery have the advantage of being readily available, and no roots are lost to digging. Further, the upper or crown part of the Over 200 varieties ofherbs plant usually can be further divided or replanted. including topiary, custom forcing, and special heirloom vegetables To prepare root cuttings, the roots are shaken free of medium and washed, if necessary. Remove the roots from We carrya large