Understanding the Turfgrass Crown
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A PRACTICAL RESEARCH DIGEST FOR TURF MANAGERS Volume 9, Issue 5 • May 2000 BACK-TO-BASICS IN THIS ISSUE • Understanding the . Understanding the Turfgrass Crown ... 1 Tlirfgrass Crown Mother of a turfgrass Leaf and bud emergence By Richard J. Hull Stems emerging from the crown his is the first of a three-part series on turfgrass morphology, function, physiology and management implications. This series will feature crowns, leaves and roots, all vitally Rhizome growth Timportant parts of turfgrass plants. Today we will concentrate on turfgrass crowns. In his recent textbook on turfgrass management (1998), Nick Christians states, "The Stolons' horizontal growth crown is the center of activi- Flowering culm ty for the turfgrass plant, and as long as it is alive the plant YOUNG LEAF Crowns as storage organs is alive." If anything, this is an FLOWERING CULM Turf management and . NODES understatement. The crown crown functions literally is the turfgrass plant, TILLER NODES • Why it T^kes IO Years or at least that which makes a to Bring Products to turfgrass a perennial plant. Market. ......... 10 The primary growing points RHIZOME AND/OR STOLON NODES (meristems) are located in • Vermiculite Scare the crown which means all Worrisome ..... 14 grass organs originate from • 16-Minute Checklist. 15 the crown. Most of the ener- gy reserves of a turfgrass plant are stored in its crown. During the winter and even during drought-induced summer dormancy, the crown may be the only part of a grass plant that survives. Considering all this, it may appear strange that most turf folks rarely think about the well-being of grass crowns Figure 1. Stylized image of a turfgrass croum with nodes when developing a turf man- identified that will contribute to a flowering culm, agement program. produce tillers, and give rise to rhizomes or stolons. Only Leaves are certainly con- the flowering culm internodes unll elongate. Roots are sidered when deciding on a much reduced for a croum old enough to have so many height of cut and the impor- nodes. All but the youngest leaf are removed. Visit us at www. landscapegroup. com TURFGRASS TRENDS Executive Editor Sue Gibson 440/891-2729; 440/891-2675 (fax) the adventitious roots which emerge from sgibson@advanstar. com tance of roots is generally acknowledged when scheduling fertilizer applications or crown nodes. The primary roots can survive Managing Editor Curt Harler aerification. Crowns are down there where for several weeks or more than a month and 440/238-4556; 440/238-4116 the leaves meet the roots and you do not make a modest contribution to the plant's [email protected] want to scalp them by mowing too close, nutrition and supply of water. Eventually, Senior Science Editor but otherwise they are not worth much they are shed and the adventitious roots Dr. Karl Danneberger attention. Today I hope to change that atti- assume the task of establishing and main- Consulting Editor taining an intimate relationship with the Chris Sann tude. soil. Root structure and function will be the Group Editor Vern Henry subject of a future report. The mother of a turfgrass For the turf manager, the most impor- Production Manager Karen Lenzen The crown is a stem from which all tant and obvious function of turfgrass 218/723-9129; 218/723-9576 (fax) other stems, leaves and most roots originate. crowns is their role in initiating leaf and klenzen@advanstar. com It is literally the mother of a grass plant. As stem development. The apical meristem is Circulation Manager positioned at the apex of the crown where Frank Christopherson long as the crown is alive and healthy the 218/723-9271 plant can survive even when all other it undergoes cell divisions, producing new Croup Publisher organs have been killed. Insects and diseases cells for leaf and nodal bud development. John D. Payne that spare the crown, even if they ravage Unlike apical meristems of broad-leaved 440/891-2786; 440/891-2675 (fax) leaves and roots, rarely cause turfgrass plants (dicotyledons), the apical meristem jpayne@advanstar. com death. Diseases such as Pythium blight and in grasses produces leaf primordia that Corporate & Editorial Office 7500 Old Oak Blvd. severe infections of stripe smut will attack retain meristematic activity at their base, Cleveland, OH 44130-3369 the crown and, in so doing, kill the plant. below the shoot apex. Mew Subscriptions The crown originates from the basal 888/527-7008 nodes of a seedling grass plant (Hull, Abstracts: 800/466-8443 1999a). Because most early shoot growth of Cell divisions Reprint: 440/891-2744 grasses involves the initiation and elonga- The cell divisions occur in a line around Permission: 440/891-2742 Single copy or back issues: tion of leaves, the stem remains just below the apical dome, giving rise to a leaf pri- Subscription/Customer Service the soil surface and experiences little verti- mordium that forms a ridge just above 888/527-7008; (fax) 218/723-9437 cal growth. This continues for some time what will become a stem node. Cells at the Web site address: www. landscapegroup. com while leaves are being produced and a root base of the leaf primordium remain meris- system develops. Both leaves and roots orig- tematic and form the intercalary meristem inate from the crown but the crown itself at the base of each developing leaf that sup- grows little except for a modest increase in ports the continued growth of that leaf W diameter (Fig. 1). ADVANSTAR even after more apical leaves have been ini- COMMUNICATIONS Leaves are produced as nodes emerge at tiated. Chairman and the stem apex but there is virtually no At any given time, most turfgrasses have Chief Executive Officer internode elongation. As with all flowering from five to 10 leaf primordia present, Robert L. Krakoff plants, a bud is formed just below the line below the apical meristem at various stages Vice Chairman of attachment between each leaf and the of development (Turgeon, 1999). Further James M. Alic stem but on the side opposite the point of leaf development from its primordium and VP-Finance, CFO & Secretary leaf initiation. Because the stem does not David W. Montgomery the phytomer concept of grass structure elongate, these buds are clustered on alter- will be discussed in a future article devoted Executive Vice President, Business Development nating sides of the crown. Such buds do not to turfgrass leaves. Skip Farber resume growth into basal shoots until the A nodal bud is initiated at the time Executive Vice Presidents plant achieves the appropriate develop- when the ring of dividing cells that will William J. Cooke mental state. become a leaf primordium completely Alexander S. DeBarr Morris R. Levitt The basal nodes of a developing crown encircles the shoot apex. A small group of Daniel M. Phillips give rise to the adventitious roots that will surface cells just below the developing leaf Vice President & General become the principal root system of the primordium and on the side opposite leaf Counsel Eric I. Lisman plant. The primary roots emerge from the initiation, begin to divide and form a new germinating seed but they are replaced by meristem. Treasurer and Controller Adele D. Hartwick This meristem develops into a nodal promote tillering. Excessive nitrogen pro- bud and has the potential of becoming a motes leaf growth but depresses tiller pro- secondary apical meristem capable of pro- duction. ducing a secondary shoot: tiller, rhizome or Tiller production is not unlimited. stolon (Fig. 1). There can be no more tillers than there are Nodal buds are formed opposite most crown buds that can develop into tillers. grass leaves; exceptions being the seed leaf With one bud per node, the number of (coleoptile), the bud scale (prophyll) and nodes in a grass crown sets the upper limit the flower scale (palea). These are all first for tillers that can be produced. leaves produced by an apical meristem of a Of course, as each new shoot (Madison, 1971) and generally leaf is initiated from arise from a node that fails to initiate a bud. the crown apex, a new Most tillering OCCUTS iïl bud is formed and 7 7 thus another potential COOlseUSOU gTOSSeS during Stems emerging from the tiller. Most grasses can the autumn and is fUOSt crown produce no more than Secondary stems can emerge from nodal 14 to 20 leaves per abundant when tempera- buds on the crown and contribute enor- stem (Madison, tures are moderate to low. mously to the ability of a grass plant to pro- 1971). duce a thick stand and spread vegetatively. Not all crown These secondary stems include tillers, rhi- buds develop into secondary shoots — zomes and stolons. some remain dormant and never resume Tillers emerge from nodal buds near the growth. Stand density influences the degree midregion of a grass crown. The buds nor- of grass tillering. More tillers per plant are mally resume growth while surrounding observed in thinly spaced plants than in leaves are still functional. Growth is posi- dense stands of grass. tively geotropic so the tiller elongates The base of each tiller develops into a upward between the sheaths of leaves. secondary crown, which remains attached Tillers are said to be intravaginal shoots to the original primary crown. As several reflecting their growth among and emer- tillers emerge from crown buds, the total gence from encircling leaf sheaths. Tillering crown structure becomes increasingly com- adds shoots to a turfgrass stand and con- plex and can enlarge substantially. The fre- tributes in a major way to increased turf density. Crown buds commence growth as tillers when the plant reaches a specific age or more likely a suitable energy status.