Three plant-based approaches to greenhouse CO2 management were explored in commercial and experimental tomato greenhouses. These were: (1) simulation modelling, (2) a non-destructive analysis of growth and (3) plant carbon status. A cost and benefit analysis using simulation modeling was carried out using grower-collected greenhouse environment and yield data. Simulation modelling was useful in a retrospective analysis for determining the costs and benefits of several CO2 dosing scenarios. However, the analysis was hampered as a CO2 management tool because key data relating CO2 production to the CO2 concentration in the greenhouse was unavailable and also because the yield model was inaccurate. Non-destructive measures of growth are collected by growers and might be useful as plant-based indicators of CO2 response. However, the measures investigated were deemed to be too sluggish to be used for CO2 dosing decision-making. Finally, plants under CO2 enrichment can accumulate substantial amounts of starch in their leaves and excess starch may indicate CO2 over-dosing. Plant carbon status was investigated by determining the distribution of leaf starch in the canopy and diurnally. These profiles led to the identification of canopy strata that are under the influence of both source and sink. The carbon status of this region maybe useful for CO2 dosing decisions and is worthy of further study.