This one gardening trick could make your roses bloom like the expensive ones in a florist’s bouquet

It can help create a more abundant display, particularly with repeat-flowering roses, but there is no guarantee of enormous, perfectly shaped blooms.
For larger individual flowers, the University of California’s Statewide Integrated Pest Management Program explains that removing some side growth and pruning appropriately can favour fewer, larger flowers with longer stems, which are useful for cut flowers. The trade-off is that the plant may produce fewer blooms overall.
Ultimately, the most useful rose-growing trick is not a secret ingredient. It is understanding how your particular rose grows, removing spent flowers when appropriate and giving the plant the light, water and nutrients it needs.