During in vitro rooting of rose ‘Madelon’ microcuttings, auxin (10 µM indole-3-acetic acid) triggered a massive synthesis of ethylene, which was released into the headspace. This resulted in an almost complete senescence of the leaves within 3 weeks. Senescence was almost completely prevented by ‘power pellets’ (porous zeolite grains coated with KMnO₄ that remove ethylene in the headspace). Rooting was not affected by KMnO₄-grains. Counteracting ethylene by silver thiosulphate (STS) was successful with respect to leaf senescence but STS inhibited rooting strongly (by 85%). KMnO₄-grains had a strong positive effect on acclimatization of the microcuttings (93% survival vs. 0% at 10 µM indole-3-acetic acid) whereas the STS-treated microcuttings died during acclimatization. KMnO₄-grains also removed other toxic organic gases from the headspace.