Sum­mer prepa­ra­tion key to tree health dur­ing win­ter

Winnipeg Free Press - Section G - - FRONT PAGE -

RE­DUCED light in­ten­sity and de­clin­ing air tem­per­a­tures at the be­gin­ning of the fall sea­son causes green leaves of most de­cid­u­ous trees (leaf-drop­ping trees) to turn colour and even­tu­ally drop from the tree. Most peo­ple are un­aware that dur­ing the sum­mer months th­ese trees are pre­par­ing for win­ter by pro­duc­ing over-win­ter­ing buds. Th­ese buds will open in the fol­low­ing spring to pro­duce new leaves, twigs and flow­er­ing parts. Gar­den­ers re­fer to this process as “bud­ding out.” Th­ese buds typ­i­cally oc­cur un­der the parts of the leaves that are at­tached to the woody twigs. Re­mem­ber, all tree buds are pro­duced dur­ing the pre­vi­ous sum­mer. Green leaves, be­fore they change colour, send all of their sug­ars and starches pro­duced by pho­to­syn­the­sis to stor­age cells in the sap­wood of branches and trunks, and in the roots. The high sugar con­tent, as well as other by prod­ucts, keep those cells from freez­ing as long as those woody plants are hardy to our win­ters. The bark pro­vides a pro­tec­tive layer for those cells. Be­low the bark is an im­por­tant re­gion called the cam­bium layer. The spe­cial­ized cells of the cam­bium layer are im­por­tant for two rea­sons: They are in­volved in the pro­duc­tion of new wood on the in­ner side of the layer (xylem cells), and the pro­duc­tion of spe­cial­ized cells on the outer side (phloem cells). Those spe­cial­ized cells al­low the trans­port of sug­ars and other car­bo­hy­drates pro­duced by the leaves to be stored in other liv­ing cells of the tree, es­pe­cially the roots. Cork-like tis­sue in the bark gets thicker with each pass­ing year, and acts as an in­su­la­tion bar­rier to the pen­e­tra­tion of se­verely cold tem­per­a­tures. Conif­er­ous ever­green trees such as spruce, pine, fir, cedar and ju­niper should not drop all of their nee­dles be­fore or dur­ing win­ter. They pre­pare for win­ter dif­fer­ently. Ever­green nee­dles and leaves (or bracts) are thick and usu­ally waxy to re­duce wa­ter loss. Very small open­ings called stom­ata on the lower side of the nee­dles al­low wa­ter to evap­o­rate dur­ing the grow­ing sea­son, but in prepa­ra­tion for win­ter, stom­ata close up to pre­vent wa­ter loss and in­jury from freez­ing. Nee­dles nor­mally do not freeze, be­cause their resin con­tent acts like an­tifreeze. On the prairies, conif­er­ous nee­dles and bracts stop pho­to­syn­the­siz­ing later in the fall. This is why ever­green nee­dles and leaves in win­ter of­ten look grey­ish-green rather than the vi­brant green or blue-green colour of sum­mer. Ever­green nee­dles and bract-like leaves do not per­sist for more than five to six years on av­er­age. They will typ­i­cally turn rusty brown as they die and fall from the tree. As I have men­tioned many times be­fore, use a burlap screen placed on the south and south­west side of smaller ever­green trees and shrubs be­fore the ground freezes hard. This will help pre­vent nee­dle brown­ing from win­ter burn. Although it is too late in the sea­son right now, trees and woody shrubs can be fer­til­ized in the early fall. They should also be fer­til­ized the fol­low­ing spring. The nu­tri­ent el­e­ments such as slow re­lease ni­tro­gen, phos­pho­rus, potas­sium and iron com­pounds along with a num­ber of mi­cronu­tri­ents in tree fer­til­iz­ers are es­sen­tial for healthy tree growth es­pe­cially for conif­er­ous ever­green trees ‘forced’ to grow on Red River val­ley soils. Michael Allen M.Sc.F., RPF (ret.) is a con­sult­ing ur­ban forester, tree di­ag­nos­ti­cian and cer­ti­fied ar­borist. He owns Vibur­num Tree Ex­perts. He can be reached at 204-831-6503 or 204-223-7709 vibur­numtrees@shaw.ca His web site is www.

tree­ex­perts.mb.ca Michael’s new book, Dr. Tree’s Guide to the Common Dis­eases of Ur­ban Prairie Trees is avail­able from the au­thor or from McNally Robin­son, Chap­ters book stores and from many lo­cal gar­den

cen­tres.

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