© 2021 Elsevier B.V.Growing long vertically aligned carbon nanotube (VACNT) forests have been achieved so far. However, it requires some additional steps or use of etchants to keep catalyst nanoparticles (NPs) active during VACNT growth in chemical vapor deposition (CVD). Here, we were able to grow a 2.6 mm long VACNT forest with a very simple and cost effective method without using an etchant or other complicated systems. Reducing the catalyst at lower temperature than the growth temperature before VACNT growth provided dense and uniform NPs formation. We observed that NPs, formed after low temperature reduction, did not coarsen at growth temperature at least for 20 min which extends catalyst NP lifetime. Moreover, we find that time varying forest height of VACNT is accurately represented by the Gompertz model of height evolution as a result of low temperature catalyst reduction otherwise it is represented by the monomolecular model. Additionally, use of very low carbon feedstock (10 sccm C2H4) enabled us to prevent carbon coating of active catalyst NPs and ensured a longer NP lifetime. Low carbon use also provided a cost effective and an eco-friendly synthesis of VACNT.