Rooting products and cutting timing for peppermint (Mentha x piperita L.) radication

Peppermint is native to Europe and has become both cultivated and naturalised in many countries, including the USA, India, China, Italy, France and Hungary. As a hybrid, peppermint seldom produces seeds that will germinate. As a consequence, the plant is propagated mostly from its vegetative parts, such as green shoots and underground stolons. Cuttings are one of the most important means of plant propagation. The aim of this research was to evaluate propagation by cuttings on peppermint, testing natural rooting hormones for organic farming and synthetic auxins with different application procedures to increase rooting. The experiments started on October 2001 and ended on May 2002, leading to 12 runs, which were done every two weeks. Treatments consisted of 7 commercial rooting products, one of which applied in two ways, leading to 8 product treatments, plus an untreated control. Trays were located on a bench provided with mist irrigation system. Starting three weeks after each cutting, 4 weekly samplings took place to evaluate rooting degree, measuring the longest root length. The experimental design consisted of a completely randomised design with rooting products as a factor (9 levels: 8 products plus control) with 4 repetitions. The use of rooting products had a positive effect on root system differentiation and development of peppermint. Six weeks after cutting the longest root was about 60 min long. Thirty-six days after cutting the longest root of cuttings treated with rooting products was significantly longer (15 mm) than the longest root of untreated cuttings. No differences were found between cuttings treated with rooting products of synthetic origin and those treated with rooting products registered for organic farming. Throughout the seasons, rooting products did not show any particularly different behaviour, but using rooting products has been necessary to guarantee the rooting of cuttings for earlier transplanting.