The results of an experimental indoor hydroponic Cannabis growing study, using the ‘Screen of Green’ (ScrOG) method—Yield, tetrahydrocannabinol (THC) and DNA analysis Glenys Knight a, *, Sean Hansen b,1 , Mark Connor a , Helen Poulsen a , Catherine McGovern c , Janet Stacey d a Institute of Environmental Science and Research Limited (ESR Ltd), Kenepuru Science Centre, 34 Kenepuru Drive, Porirua, New Zealand b Organised Crime Unit, Wellington Central Police Headquarters, Wellington, New Zealand c Institute of Environmental Science and Research Limited (ESR Ltd), Mount Albert Science Centre, Auckland, New Zealand d Forensic Science Program, Department of Chemistry, University of Auckland, New Zealand 1. Introduction 1.1. The New Zealand environment New Zealand is the most geographically isolated country in the world. It lies in the South Pacific Ocean, approximately 2250 km to the east of Australia and just to the west of the international dateline. While New Zealand is comprised of a group of narrow islands spanning nearly 138 of latitude, from the subtropical to the subantarctic, its main land areas experience a predominantly temperate climate, strongly influenced by the surrounding oceans. The population of just over 4.3 million people is highly urbanised, with over 86% living within the urban areas, which comprise just 2.7% of the total land area [1,2]. The remaining large areas of land, occupied by indigenous forests and reserves or under forestry or pastoral cultivation, provide ample opportunities for the covert cultivation of Cannabis crops outdoors, and to date most of the Cannabis seized in New Zealand has been grown outdoors. In the warmer, northern areas of New Zealand staggered planting allows the harvest of two crops per year, with a first phase of harvesting in early December producing a pre-Christmas crop which achieves very good prices, and a second phase of harvesting in February to March [3,4]. In most of New Zealand however, only one outdoor crop is possible annually, with the typical cultivation period being between September and March. All drug-Cannabis in New Zealand has originally been illegally imported in the form of seed, with much of this either purchased Forensic Science International xxx (2010) xxx–xxx ARTICLE INFO Article history: Received 22 September 2009 Received in revised form 12 April 2010 Accepted 13 April 2010 Available online xxx Keywords: Cannabis Hydroponic cultivation Screen of Green (ScrOG) Yield Tetrahydrocannabinol (THC) DNA ABSTRACT The results of an indoor hydroponic Cannabis growth study are presented. It is intended that this work will be of assistance to those with an interest in determining an estimation of yield and value of Cannabis crops. Three cycles of six plants were grown over a period of 1 year in order to ascertain the potential yield of female flowering head material from such an operation. The cultivation methods used were selected to replicate typical indoor hydroponic Cannabis growing operations, such as are commonly encountered by the New Zealand Police. The plants were also tested to ascertain the percentage of the psychoactive chemical D-9 tetrahydrocannabinol (THC) present in the flowering head material, and were genetically profiled by STR analysis. Phenotypic observations are related to the data collected. The inexperience of the growers was evidenced by different problems encountered in each of the three cycles, each of which would be expected to negatively impact the yield and THC data obtained. These data are therefore considered to be conservative. The most successful cycle yielded an average of 881 g (31.1 oz) of dry, groomed female flowering head per plant, and over the whole study the 18 plants yielded a total of 12,360 g (436.0 oz), or an average of 687 g (24.2 oz) of dry head per plant. THC data shows significant intra-plant variation and also demonstrates inter-varietal variation. THC values for individual plants ranged from 4.3 to 25.2%. The findings of this study and a separate ESR research project illustrate that the potency of Cannabis grown in New Zealand has dramatically increased in recent years. DNA analysis distinguished distinct groups in general agreement with the phenotypic variation observed. One plant however, exhibiting a unique triallelic pattern at two of the five loci tested, while remaining phenotypically indistinguishable from three other plants within the same grow. ß 2010 Elsevier Ireland Ltd. All rights reserved. * Corresponding author. Tel.: +64 4 914 0632; fax: +64 4 914 0640. E-mail address: glenys.knight@esr.cri.nz (G. Knight). 1 Now at Organised Crime Unit, Eastern District Police Headquarters, Napier, New Zealand. G Model FSI-6044; No. of Pages 9 Please cite this article in press as: G. Knight, et al., The results of an experimental indoor hydroponic Cannabis growing study, using the ‘Screen of Green’ (ScrOG) method—Yield, tetrahydrocannabinol (THC) and DNA analysis, Forensic Sci. Int. (2010), doi:10.1016/ j.forsciint.2010.04.022 Contents lists available at ScienceDirect Forensic Science International journal homepage: www.elsevier.com/locate/forsciint 0379-0738/$ – see front matter ß 2010 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.forsciint.2010.04.022