Metallocenes are toxic chemical that is used for the growth of carbon nanotubes. The study of toxicity of metallocenes on plants is very important. It governs the issues of genetics. The toxicity studies should be considered with (I) studies of growth kinetics of carbon nanotubes, (II) studies of chemical reaction of metallocenes inside carbon nanotubes, and (III) investigations of the electronic properties of filled carbon nanotubes. The toxicity studies are influenced with the investigation of growth process of metallocene-filled carbon nanotubes, evaporation of metals, formation of multiple-walled carbon nanotubes. The toxicity studies are also influenced by investigations of the modification of the Fermi level of filled carbon nanotubes. Metallocenes are filled inside carbon nanotubes with different methods, which are discussed here. They include the solution methods, gas phase method, which are different in methodics and require optimization. Many authors published different methodics of filling of carbon nanotubes with metallocenes. They lead to high filling ratios, and allow future modifications of the electronic properties of carbon nanotubes. Kinetics of growth of carbon nanotubes is investigated with different methods. Environmental transmission electron miscroscopy is applied to study with the time resolution of several nanoseconds. Here, we use Raman spectroscopy to study the growth process, which is revealed with activation energies, growth rates, temperature dependence. This is needed for tailoring the toxicity of metallocene-filled carbon nanotubes on plants.