Good example of "contamination" discussed in a Boston Globe article I read recently. The "herbal" tea Pai You Guo contains the weight loss drug silbutramine, and a possibly carcinogenic compound, phenolpthalein. Despite an FDA-announced recall the product remains on the shelves at some shops. Apparently certain "herbal" products depend on the hidden presence of pharma drugs which can cause harm, especially if consumers are unaware and/or if the drugs are no longer supposed to be used because of known dangers.

brendan is correct; it should be noted though that these examples do not involve what we commonly consider to be drugs (i.e. they are not used to treat illnesses). And alternatives are available; for example in the case of flu vaccine, the minute amount of preservative can be avoided entirely if one is concerned about it. As I noted recently in another thread, answering a concern about a herbal treatment with an attack on mainstream medicine misses the point. Even if we were to believe that evidence-based medicine is the epitome of Evil, it wouldn't relieve herbalism of the obligation to provide safe and effective remedies.

[quote]R2 as we know it in America is quite low for house insulation. I used that number to allow for our test greenhouse to have 6mm twinwall on the south and south roof and some insulation on the North walls etc.[/quote] Heh, perhaps I'm just weird then, but I have metric R2 on my north wall (+parts of east and west, +underground) and about metric R 1.4 for the glazing. Metric R values are about 0.17 times US R values. [quote]I am sorry but many here with small greenhouses are infact coming as close to an hermetically sealed structure as possible. 10-20 tubes of calking... on a 6x8ft? [/quote] Well, it depends on what the caulk is being used for. I caulked my insulation on. Let me tell you, that takes a lot of caulk. Even if you seal up all of the cracks, I would be surprised if the small amount of circulation couldn't occur through things like: * The drainage system * Between panes of closed vents * Through the zipper or doorframe. Sure, a vent is a good idea. But we're talking about needing a very small amount of air indeed. [quote]Also in this thread nobody has mentioned the water. Unvented heater, sealed up as best you can, no air exchange. Adding CO2 by burning propane makes it wet in there too.[/quote] That is true. The moisture beads on the glazing and runs down to the floor; it's like a jungle in there (when I wear glasses, it's instant fogging when I walk in). I haven't grown any plants that are sensitive to moisture-related diseases before, but I've got some in the seedling stage right now, so we'll see if they complain. They're doing quite beautifully so far (I could get pictures if you like), but moisture-loving diseases like powdery mildew take some time to get established. I'll get back to you about them in a month or so and let you know how they compare to the equivalent plants grown outside this summer. [quote]stressbaby, Gladly. Greenhouse cucumber operation in Calif. with newly installed unvented heaters. After a cold winter period, severe damage was noted on the crop. Air samples analyzed showed elevated levels of ethylene and mercaptan.[/quote] Elevated *mercaptan* levels? Wow, that heater must have been doing an awful job. Mercaptans are only in PPM quantities to begin with, so if you're having measurable amounts *after* combustion, something is seriously wrong there. [quote]economic losses to greenhouse growers from ethylene pollution are reported each year[/quote] You do realize, I presume, that ethylene pollution can happen even when no heater is used. Decaying plant matter is an especially bad ethylene producer, but even healthy plants produce it (some species more than others). [quote]For an interesting thread from about a year ago, complete with more examples of problems with unvented heaters, use the search function, type "carbon dioxide" and read the posts on "plants suffering from propane". Some noted problems in other "real-life" situations.[/quote] Well, for your information, with Thanksgiving dinner, my main course was a delicious vegetarian lasagne made with a heaping handful of basil from my "suffering" greenhouse basil plants. Last night for dinner, I had pasta primavera made using some of my "suffering" tomatoes. My point? A proper installation doesn't have problems. An improper installation does. Notice how you haven't gotten into the risks of the other common hobby greenhouse heating system, electric. You know, a box of resistors with large amounts of current flowing through it, in a moist environment that usually has a metal frame, and plenty of combustables within, possibly even standing water? I read the "suffering from propane" thread before I got my heater. I read enough from elsewhere to realize that this person had an improper installation. Notice -- it only took a few days of use of their heater for problems to occur. Mine has been running for two months this winter. Note what was mentioned in the thread: "Sometimes the smell is very strong." Huge red flag right there. Properly combusted propane/natural gas has no smell. The instant they smelled it, they should have disconnected the heater -- it sounds like a leak. Note what others said in the comments trail, such as Orchiddude and trigger_m (who also provided pictures). [quote]One factor missed in this thread was ethylene.[/quote] Ethylene was already mentioned several times in this thread. Use your browser's search function; you'll find it.

Laura, I'm glad you brought this thread back to life, because I have never found it. Al, as always, is very informative and reasonable. I agree whole heartedly with how he approaches gardening. I too prefer to use compost, and avoid chemicals, but am not against using chemicals either. For example, I refuse to sit back and watch my garden be destroyed by insects because I don't want to use chemicals. Usually I don't need to, but if things get rough, I have to bust out the big guns. Anyways, Laura, you talked about the runoff problems in your area; these issues come up all over, including here in WI. The biggest misconception people have is that the people using the "nasty" chemical fertilizers are causing the runoff, when in fact runoff problems can be caused by organic fertilizers as well. The biggest issue is not the stuff causing the problems, but the people who are. Proper use of inorganic AND organic fertilizers is key. You can buy all sorts off different products, both organic and inorganic, and each has instructions as to the proper application. If you don't follow these instructions, well, that is where the problem lies. So, with that said, you seem like a very reasonable and responsible person, so whether you apply organic fertilizer or synthetic fertilizer, and can assure you that if you follow the directions, you personally are NOT contributing to the runoff problems. Again, thanks to Al for his infinate wisdom, and to Laura for bringing this one back to life. Joe