Compactness is a desirable trait in ornamental plant breeding because it is preferred by producers, distributors and consumers. Presently, in ornamental plant production growth of many potted plants is regulated by application of chemical growth retardants, several of which are harmful to both the environment and human health. With the aim to develop an alternative to chemical growth regulators, a biotechnological approach without the use of recombinant DNA technology has been developed. In this method, the soil borne bacterium Agrobacterium rhizogenes inserts T-DNA, containing four root oncogenic loci (rol)-genes rolA, rolB, rolC and rolD among 18 ORFs, into the plant genome. Infection of plants by A. rhizogenes induces hairy roots, from which shoots containing rol-genes can be regenerated. Natural transformation with A. rhizogenes reveals very promising results in several plant species and can be useful in a broader range of application than ornamental breeding. One important aspect of this technology is that the hairy roots can be used directly in the selection proceß as a primary indicator of a succeßful transformation. Thus the technology avoids use of undesired antibiotic resistance marker genes. Noteworthy, in Denmark the authorities have confirmed that plant products developed using natural transformation by unmodified strains of A. rhizogenes are not considered as genetically modified (GM) plants according to the European legislation. Generally, rol-genes cause increased rooting, decreased plant height, short internodes, reduced apical dominance and changes in flower characteristics. Several of these traits improve ornamental plant quality and may also benefit characteristics useful in agricultural field crops. In addition, a number of regenerated plants derived from hairy roots contain higher contents of secondary metabolites compared to wild type plants. Hence, this method also has potential as a tool for boosting high value compounds in medicinal plants.