Crna topola (Populus nigra L.) je jedna od najznačajnijih europskih vrsta drveća koja nastanjuje aluvijalna staništa uz obale velikih rijeka. U Bosni i Hercegovini postoji značajan neiskorišten zemljišni potencijal pogodan za reintrodukciju autohtonih crnih topola, kao i podizanje intenzivnih i ekstenzivnih nasada hibridnih i američkih crnih topola. Cilj ovoga istraživanja je utvrditi početak i završetak fenoloških faza listanja, kao i zimsko zadržavanje lista, što će pomoći pri selekciji pogodnih klonova autohtonih crnih topola za reintrodukciju na određenom lokalitetu i za određene mikroklimatske uvjete u svrhu očuvanja autohtonog genofonda, te klonova hibridnih topola za osnivanje plantaža u Bosni i Hercegovini. Istaživan je materijal 161 klona autohtonih crnih topola iz 26 populacija iz slivova 6 rijeka, te 11 klonova proizvodnih hibridnih topola (euro-američke ili kanadske) i američkih crnih topola. Klonovi se nalaze u klonskom arhivu u Žepču, koji je podignut 2006. godine. Promatrana je fenologija listanja i to od 14.3.- 22.4.2019. godine i to u šest fenoloških faza 0 - uspavani pupoljak, 1 – napukli pup, 2 – probijanje pupa, 3 – pup otvoren, listovi skupljeni, 4 – listovi se razdvajaju, 5 – listovi potpuno razvijeni). Zadržavanje lista praćeno je od 30.8.-4.11.2019. godine i ocjenjivano u tri kategorije: 1 - prisutni svi listovi na stablu, 2 - 50% listova je preostalo na stablu, 3 – nema preostalih listova na stablu. Efektivna duljina vegetacijske sezone definirana je kao vrijeme između pojavljivanja faze pucanja pupova (ocjena 3) i ocjena opadanja lišća 2 (tj. kada je 50% lišća ostalo na stablu). Analiza varijance pokazala je statistički značajne razlike između klonova iz različitih populacija za duljinu trajanja fenoloških faza listanja. Fenološka faza 1 (napukli pupovi) najranije se javila 14.3. a faza 5 (potpuno otvoreni listovi) najranije 8.4. Rezultati zadržavanja listova pokazuju da su 4.11. svi klonovi u klonskom arhivu odbacili list 100%. Najkraću efektivnu duljinu vegetacijskog perioda imali su klonovi populacije Bugojno (154 dana), a najdužu klonovi Populus boleana i Populus nigra var. italica te klonovi populacija Čapljina (sliv rijeke Neretve); Dobrinje, Visoko, Babina rijeka, Maglaj, Doboj (sliv rijeke Bosne); Kopači i Tegare (sliv rijeke Drine). Rezultati istraživanja su značajni za odabir klonova sa boljom prilagodbom na uvjete staništa, te obnovu i uporabu klonskog reprodukcijskog materijala crnih topola u Bosni i Hercegovini. Black poplar (Populus nigra L.) is a species growing in flood forests and today it is one of the most endangered species in Europe. In Bosnia and Herzegovina, there is significant area of unused land suitable for the reintroduction of autochthonous black poplar and the establishment of intensive and extensive plantations of hybrid and American black poplar. This research aims to determine the beginning and the end of the phenological phases of leafing, as well as the winter retention of leaves, which will help in the selection of suitable clones for the establishment of plantations in Bosnia and Herzegovina. The material of 161 clones of autochthonous black poplars from 26 populations from the basins of 6 rivers, and 11 clones of production hybrid poplars (Euro-American or Canadian) and American black poplars was analyzed. The clones were located in the clonal archive in Žepče, which was established in 2006. Leafing phenology was observed from March 15 to April 22, 2019, and during six phenological phases: 0 - dormant bud, 1 - cracked bud, 2 - bud breaking through, 3 - bud open, leaves gathered, 4 - leaves separate, 5 - leaves fully developed. The retention of the leaves was monitored from August 30 to November 4, 2019, and evaluated in three categories: 1 - all leaves on the tree are present, 2 - 50% of the leaves are left on the tree, 3 - there are no leaves left on the tree. Analysis of variance showed statistically significant differences between clones from different populations for the duration of the leafing phenological phases. Phenological phase 1 (buds breaking through) occurred at the earliest on March 14 and phase 5 (fully open leaves) no earlier than April 8. The results of leaf retention show that on November 4 all clones in the clonal archive fully rejected the leaves. The shortest effective length of the vegetation period had the clones of the Bugojno population (154 days), and the longest the clones of Populus boleana and Populus nigra var. italica and clones of the Čapljina population (Neretva river basin). Dobrinje, Visoko, Babina Rijeka, Maglaj, Doboj (Bosna river basin), Kopači and Tegare (Drina river basin). The results of this research will be used in the selection of the most suitable clones for reintroduction in a specific locality and for specific microclimatic conditions, especially the occurrence of late spring and early autumn frosts, for the purpose of preserving the autochthonous gene pool, as well as clones of hybrid poplars for the establishment of clonal plantations. It is necessary to continue phenological research in the clonal test of autochthonous black poplars and hybrid poplars in Bosnia and Herzegovina, as well as to conduct research on growth properties in order to be able to compare the results of phenological research, i.e. the length of the growing season, as well as thickness and height growth.