The best way to grow strong upright rose stems is to bend them over

Bending rose stems dramatically increases photosynthesis.

If you want to improve flower shoots in roses, then you should bend some of the shoots. The presence of bent shoots increased plant photosynthesis by 73% to 117%, whereas it did not affect photosynthesis of upright shoots,” say Nigyi Zhang and colleagues in their paper Quantifying the contribution of bent shoots to plant photosynthesis and biomass production of flower shoots in rose (Rosa hybrida) using a functional-structural plant model. “[M]odel simulations of photosynthesis revealed that the increased upright shoot dry weight (by 35% to 59%) in plants with bent shoots was entirely resulting from the contribution of additional photosynthesis by bent shoots, as this was the only assimilate source that could induce differences in upright shoot growth apart from their own photosynthesis.”

Folding rose stems is a common technique in horticulture in order to improve the flower-bearing stems. The idea is that by bending stems, you increase the surface area for photosynthesis. “However, bent shoots are lower down in the canopy and only receive limited amount of light,” say Zhang and colleagues. “Keeping too many bent shoots may therefore lead to a negative carbon balance, especially in the lower layers of bent shoots…, resulting in competition between bent shoots and upright shoots for assimilates produced by the whole plant canopy. To optimize the number of bent shoots and to maintain upright shoot quality, it is imperative to quantify to what extent photosynthesis by bent shoots may contribute to upright shoot photosynthesis and biomass production, and how this depends on bent shoot number. No studies have ever quantified such contributions.”

In order to measure the input of bent stems, the team grew roses with either zero, one or three bent stems. They created a functional-structural model of the roses to calculate what photosynthesis was going on, and the contribution of the stems. They found that bending a stem increased photosynthesis by 73% and bending three stems by 117%. This lead to an increase in upright shoot dry weight. With one stem bend the upright shoot increased by a third in mass, and with three shoots by almost two-thirds.

“Based on our simulations, we conclude that in cut-rose production, the increased flower shoot dry weight and quality can almost entirely be attributed to the assimilate supply from bent shoots,” say the authors. They also note that similar functional-structural plant models can be used to examine the effects of leading and pruning on other plants.”