The aim of this experiment was to assess how the interaction of two treatments influenced the growth and flowering of two varieties of Panicle hydrangea shrubs. The first treatment was plant pruning. Simultaneously, the plants received one of the three following treatments: root application of Trichoderma atroviride, root application of BlackJak biostimulant, or foliar application of a multi-component fertilizer. Simultaneous pruning and inoculation of the plants with the Trichoderma atroviride mycelium improved the length of hydrangea shoots the most, as compared with the control plants (18%). These two treatments also increased the number of flowers (16–47%, depending on the variety) and the fresh weight of plants (10–28%) compared with the control plants. T. atroviride alone improved the number of flowers in both varieties (19–24%) and the diameter of inflorescences in the ‘Silver Dollar’ one (17%). The foliar nutrition increased the fresh weight of plants by 7–57%, depending on the cultivar and pruning. It also increased the diameter and number of inflorescences in one of the varieties. Together with pruning, it intensified the growth of shoots in both cultivars (5–10%). The BlackJak biostimulant treatment gave ambiguous results. In combination with pruning, it improved the length of shoots (15%) in one cultivar and the fresh weight in the other (18%). Without pruning, the treatment increased the number of flowers (16%) and the diameter of inflorescences (9%) in one cultivar. It increased the fresh weight of plants in both cultivars (19–21%). Regardless of the other treatments, pruning increased the length of the shoots and the fresh weight of the plants. On the other hand, it reduced the number of flowers and their diameter. In most cases, the biostimulant treatment and foliar fertilization improved the growth and flowering of the plants. In combination with pruning, they improved the growth of the hydrangea shrubs but reduced the number and diameter of flowers. The simultaneous Ta treatment and pruning were the most beneficial for the growth and flowering of the panicled hydrangea plants grown in containers in a nursery.