Cut-flower roses are now propagated by cuttings and are grown on their own roots in soil-less substrates.
In the research described here, shoots were cut into 20cm-long cuttings bearing at least three leaves. The bases of all cuttings were dipped either into water or into water containing 1g per litre of indole-3-butyric acid (IBA). The bases of one group of cuttings were then inserted into small rockwool cubes and the cuttings were stood upright on a propagation bench.
With another group, the tops of the cuttings, too, were dipped into either water or water containing different amounts of IBA. With this group, both the bases and the tops were inserted into rockwool cubes and the cuttings were then placed horizontally on the propagating bench.
After 60 days, the cuttings were planted in perlite but still oriented as during propagation. Consequently, unit area of bench contained either 60 "vertical" cuttings or 40 "horizontal" ones. Applying IBA to the cutting bases promoted rooting, as expected, but rooting at the tops occurred reliably only with 4g IBA per litre.
Plants propagated and grown horizontally produced significantly more flowers per cutting but their productivity per unit area of bench was lower than with vertical cuttings.
Bilateral Rooting and Flower Production in Rosa hybrida Cuttings by Gudin and Crespel (2008). Journal of Horticultural Science & Biotechnology 83 (4): 474-476. The authors' abstract of their manuscript can be seen in full at www.jhortscib.com.