Agricultural Extension Service The University of Tennessee PB 1610 Flowering Bulbs for Tennessee Gardens 1 Contents Bulbs ........................................3 Corms .......................................3 Tubers .......................................3 Rhizomes .....................................4 Culture ......................................4 Introduction ................................4 Site Selection ................................5 Site Preparation ..............................5 Selecting Plant Material ........................5 Planting Spring-Flowering Geophytes ................6 Iris .......................................6 Planting Summer-Flowering Geophytes ..............7 Caladium ..................................7 Canna .....................................8 Dahlia .....................................8 Gladiolus ..................................9 Maintenance of Geophytes ....................... 10 Forcing Spring-Flowering Geophytes in the Home ... 11 Forcing Tender Geophytes in the Home ........... 12 Amaryllis ................................. 12 Dictionary of Bulbous Plants ...................... 13 The Bulb Selector .............................. 21 Mail Order Sources ............................ 22 U.S.D.A. Hardiness Zone Map .................... 23 2 Flowering Bulbs for Tennessee Gardens Mary Lewnes Albrecht, Professor and Head Ornamental Horticulture and Landscape Design wealth of spring-, are thick, fleshy, modified corm does not summer- and fall- leaves, the scales. The scales persist from A flowering bulbs can are organized to form two season to be used to extend the garden distinct types of bulbs. Lami- season. Rather, floral display from early nate (tunicate) a new corm is spring until late fall. Some of bulbs are formed above Gladiolus these will be winter hardy concentric, the old corm formed the and remain in the ground cylindrical previous year. Gladiolus and year-round. Others will not scales. The crocus are the two most survive freezing temperatures outer layers of commonly grown corms. and must be replanted each Lily scales become spring. Many are not even dry and Tubers: true bulbs, but are often sold papery, forming the tunic. Tubers are along side true bulbs in mail This protects the bulb from produced order catalogs and at garden disease, insect and mechani- when the tips stores. The different types of cal damage. Daffodil and of a stolon (a underground storage struc- onion are common tunicate horizontally tures that are frequently bulbs. The scaly (non-tuni- growing stem called bulbs include corms, cate) bulb has numerous just at the soil Caladium tubers, tuberous roots, tuber- individual scales which line) becomes ous stems and rhizomes. readily break off the basal swollen from stored foods. These underground storage plate. This bulb has no tunic, Tubers are formed below structures collectively are making it somewhat more ground. Close examination of called “bulb-forms” or geo- susceptible to disease, insect the tuber will reveal typical phytes. Geophyte comes from and mechanical damage. Lily stem structures of nodes, the the Greek word geo — mean- is a common scaly bulb. “eyes” of a potato and intern- ing earth, and the Greek odes. Besides the Irish po- word phyte — meaning Corms: tato, another commonly growth or plant; therefore, A corm is grown tuber is caladium. geophyte means “earth the swollen The tuberous root and the growth” or “earth plant.” base of a stem tuberous stem are commonly with typical Crocus mislabeled as tubers. The Bulbs: stem parts: tuberous root The true bulb nodes and internodes. The forms from the consists of a dry, papery leaf bases en- swelling of roots. much-com- close the swollen stem base, Tuberous pressed, fleshy forming the protective tunic. roots do stem, the basal The tunic, as with the bulb not have plate. Attached tunic, protects the corm from any fea- to the basal plate Dahlia Daffodil disease and water loss. A tures 3 common to stems (there are The pachymorphic rhizome and make an attractive addi- no nodes or internodes is a large, fleshy, horizontal tion to gardens: perennial present); they have all the stem which has determinate border, naturalized areas, internal and external features growth. Once the terminal rock gardens, foundation of roots. growing point or meristem of plantings, flower borders and On the other hand, the the rhizome forms an inflores- containers. Areas to avoid tuberous stem does have cence (the flower stalk), the include painted walls, paved features of stems. The tuber- rhizome will form two branches walks or driveways. Reflected ous stem forms from the behind the meristem. The heat from these areas during swelling of the area of the bearded iris is a very common midday through late after- plant known as the hypo- pachymorphic rhizome. noon can cause damage to cotyl. This is the transition most plants. If such an area is region between the root and chosen, the plants will de- the stem. velop and flower faster. The Tuberous roots are formed Culture: main disadvantage is the on the sweet potato and the Introduction foliage will die back more dahlia. Tuberous stems are quickly due to excessive heat. Geophytes are normally formed by tuberous begonias, grouped based upon their cyclamen and gloxinia. ability to withstand freezing weather. Knowing this Rhizomes: information is essential to A rhizome is a specialized proper culture. stem which grows just at or Hardy geophytes, once below the soil surface. There planted and established, will are many economically survive freezing temperatures important plants which under normally good growing form rhizomes conditions. Examples of hardy including geophytes are narcissus, tulip, bamboo, hyacinth, crocus, lily and iris, lily- bearded iris. Semi-hardy Iris of-the- species may be hardy in valley and many grasses. somewhat milder climates, but There are two types of cannot be relied upon to rhizomes found in nature, survive extended exposure to leptomorphic rhizome and below-freezing temperatures. pachymorphic rhizome. The Many of the anemones, Lily lily-of-the-valley has a ranunculus, bulbous iris and This will result in bulb de- leptomorphic rhizome: a very cannas fall into this class. cline, since not enough food thin rhizome with indetermi- Those species which will will be stored before complete nate growth (the rhizome not tolerate hard-freezing die-back occurs. Planting does not terminate in a flower temperatures and can only be under trees with surface roots stalk; it remains vegetative), left in the ground in warm such as Norway maple, beech branches freely and forms climates are referred to as or linden should be avoided, many flowering shoots. tender. This includes many of since there will be competi- Plants with our summer-flowering geo- tion between tree roots and leptomorphic rhizomes phytes such as dahlia, gladi- bulbs for necessary moisture can form olus, caladium, callas and and nutrients. For the same very tuberous begonia. reason, vigorous shrubs, such dense The bulbous plants can be as forsythia and Pfitzer juni- mats. Calla-lily used in a number of ways pers, and dense ground 4 covers, such as ivy, pachys- added to improve drainage. problem using bonemeal is andra or creeping euonymus, The third essential criteria that it attracts squirrels and should also be avoided. Many is adequate air circulation. Air similar pests that may dig up larger spring-flowering, circulation is necessary to the bulbs. If an inorganic bulbous plants will compete reduce the incidence of dis- fertilizer is used, select one successfully with the ground ease with these plants. with low nitrogen and high cover Vinca minor, periwinkle. phosphorus, such as a 1:3:1 Also consider adding many to Site Preparation or 1:3:2 N-P2O5-K2O ratio. perennial beds where the If the chosen site has poor Check the package directions perennials can actually hide drainage, several things can for the proper rate. Be sure to the unsightly bulb foliage as be done. Drain pipes can be take a soil sample to deter- it dies. laid to facilitate the removal of mine pH. Most geophytes excess water. If this is not grow best at a pH range of Site Selection desirable or feasible, adding 6.5 to 7.2. All nutrient When choosing a site, organic matter to a heavy clay amendments should be consider sunlight, drainage soil will improve drainage. incorporated into the 2-inch and air circulation. Most Adding up to 30 percent layer of soil upon which the geophytes require a minimum organic matter by volume will bulbs, corms, tubers and of five to six hours of daily make a difference (spread a 4- rhizomes will be set. sunlight. Notable exceptions inch thick layer of organic are lily-of-the-valley and matter over the bed then till it Selecting Plant caladium, which can thrive in into the soil to a depth of 12 Material shade (see the Dictionary of inches). Adding organic When buying any flower- Bulbous Plants and The Bulb matter from composts will ing bulbous plants, it is best to Selector lists at the end of this also aid sandy soils where buy from a reputable dealer. publication for others). For drainage is too rapid and Some minor or unusual bulbs maximum growth from year water-holding capacity is have been illegally harvested to year, eight to 10 hours of reduced. If the area has such from the wild. These should be sunlight are better. Adequate poor drainage that organic avoided. Also, avoid the “bar- sunlight results in larger matter incorporation will not gain” bulbs. Much of the plant blooms and healthier, hardier be of much benefit, raised material offered at reduced plants due to the ability to beds can be constructed. prices are low grades (smaller maximize photosynthesis. Materials such as landscape bulbs). Low grades will not A sandy loam is the best timbers, stone or brick can be produce as large a flower or type of soil for geophytes, used to build raised beds. may not flower at all. More since it has very good drain- Walls can be made high often than not, you will be age coupled with good water- enough for use as additional disappointed in plants resulting holding capacity. To check an seating in the smaller gardens from inferior grade material. area for drainage, dig a hole of today’s urban settings.