Dahlia is one of the most important cut flowers and it is used also for garden decor during the summer. Based on the researches conducted on seven cultivars of Dahlia hybrida cactus type: 'Kennemerland', 'Tsuki Yori No Sisha', 'Hayley Jane', 'Purple Gem', 'Star Favourite', 'Park Princess', 'Friquolet', it was analysed the influence of cultivar and planting material (forced and unforced tuberous roots) on some phenological aspects. Phenological observations conducted on the plants were the following: debut of growth, appearance of the first flower buds, opening of the first flower buds and decorative period. According to the data collected, it was calculated the duration between phenophases as number of days. After the interpretation of the results using Ducan test, it was found that forcing of the tuberous roots has a positive influence on the duration of decorative period, that took place in an interval of 58.11-112.55 days for the cultivars 'Park Princess' and 'Kennemerland' and by comparison, for the unforced tuberous roots, the decorative period was much shorter for cultivars 'Star Favourite' (29.77 days) and 'Kennemerland' (105.55 days). Studies reveal that forcing of the Dahlia tuberous roots is causing the decrease of number of days from planting to sprouting that also helps in extending the decorative period.