Just because a few people say its a bad thing doesnt mean its true... logically thinking it sounds like a bad thing. But like the other guys i would like to see a type of experiment to show for one side or the other. Even if an experiment proved it is not harmful to your plants at all doesnt mean im going to immediatley go and smoke a cig next to my plants but it would be nice to know FOR SURE if it would harm your plants or not.
Likewise, just because a few people say its fine doesn't mean it is. If logic and common sense suggest that it could be harmful, and you ignore it, then you are abandoning reason. An experiment would be nice, and it would probably set a lot of things straight for those of you demanding evidence. However, it seems a little pointless. The answer seems fairly obvious. I dont mean to sound like a know it all or anything, you are asking an honest question, but some of these answers are painful to read!! Do you guys think that botanists and professional growers smoke cigarettes in their lab? No way! Besides that, if you know a little bit about how plants function you would be able to put the pieces together with very little difficulty. It makes so much sense when you think about the actual science involved. I'll try to explain to the best of my knowledge, but doing your own research elsewhere will provide a better understanding. Believe it or not, they do have the answer to this question
First off, I smoke a good 3 or 4 packs a week, and if you saw me, you would think I was just fine too. Im alive, im physically active, and I generally feel pretty good, but that's not the reality. It's nice to think that cigarette smoke doesn't do you any harm but you know damn well its messin things up inside. So the assumption that your plant is healthy because it looks healthy and doesn't have any problems is just that, an assumption. Or it's a self affirmation that is used to excuse the behavior and allow you to smoke shamelessly around your plants. Honestly i smoked buds around my plants all the time, i used to blow a big ol hit their way every single day, even now it doesn't seem like it matters so much. So if you wanna light one up in the grow room go on ahead, i dont think most people really even think about it. Im not here to tell you whether you should or shouldn't, I just want to burn it into your heads that cigarette smoke is not healthy for plants and can potentially damage crops.
Pretty much every plant on dry land (including cannabis) have pores on their leaves called stomata which are responsible for gas exchanges with the environment. They are like nostrils for a plant. They open and close depending on environmental factors such as available CO2 and sunlight, as well as internal factors like having too much oxygen or even H20.
Every cigarette leaves thousands of chemicals and carcinogens that DO IN FACT CLOG THE STOMATA!!! No data needs to be obtained, because its not really a question as far as I know. Since many of you tend to ignore this fact I will put it into perspective. Leaves are like sponges, they absorb everything, some plants dont even get nutrients from soil because so much is obtained through the air. So pollutants like tar and carbon monoxide from even one puff will eventually find there way into the thousands of stomata making it more difficult for respiration. If a plant cannot release a certain amount of oxygen then it will not absorb a certain amount of CO2, thus a certain amount of productivity will be lost or slowed. You might not be able to see it, but even fast moving air propelled by a fan is absorbed. It doesn't need to settle in the room for it to be harmful (although if a plant is exposed to conditions where smoke has settled around it these effects will likely worsen). Again, you may not be able to see the negative effects of this, plants are very resilient and do a pretty good job at coping, but the effects are taking their toll.
This isnt the only reason why resources will be cut off though (oh no, doesn't stop there!) smoking around a plant throughout its life cycle will inevitably result in less stomata on each leaf to match available CO2. I cant imagine you would lose a whole lot if you smoked around them once or twice a week, but overtime a plant learns the limitations of its environment and adapts accordingly.
So there are a few examples of how cigarette smoke and its residual toxins effect photosynthesis and respiration in the leaves. Now lets consider the roots. I've kinda always suspected that cigarette smoke isn't something I wanted around my leaves, but I didn't really think about how the root system was effected until I started using aeroponics. Inside a five gallon bucket I have a mist like environment that recirculates a nutrient solution into the air where the roots hang down. I've also got a bubbler in the reservoir that takes air from the grow room and pumps it straight into my solution. If a plume of smoke comes anywhere near that aquarium pump you can bet your sweet ass its gonna end up in my solution. That carbon monoxide will destroy the beneficial population of microorganisms that are so important to nutrient uptake. Essentially this will decrease the uptake of nitrogen by killing off the bacteria that fix nitrogen in the first place and since carbon monoxide can be absorbed by the roots, less oxygen and less nutrients will be.
I researched this because I was worried about a specific growing medium, but I learned that it could be potentially hazardous for ANY growing medium, and that means soil too. In extreme conditions a plant will die from cigarette smoke! So do as you may, but be mindful of the physiological implications that come along with smoking.