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Greenhouse questions?

First, I would like to say hi to all you fine people here and thank you in advance for your help. Let me introduce myself. I am the director of a small life rehabilitation center close to Abilene, TX. We are a freewill supported facility that provides free services to people suffering with addictions, depression and such things. Needless to say, we don't have a lot of money. We are constantly looking for ways to become more efficient and future proof our operation so that we may continue to operate even if economic times get rough and we loose the majority of our support. For this reason, I am looking into greenhouses as way to grow vegetables naturally, year round. I have been doing a lot of research and I am not finding clear answers to my questions, so I thought I would post them here for you experts to see.

If we are going to go down this path, I want to make sure it will be effective and efficient for our purpose. But since we have a very limited budget to devote to this project, I have to find a way to economically overcome the biggest obstacles to effective year round greenhouse production which I believe to be, summer heat, winter cold and humidity control. So I will tell you what my thoughts are and what I think might work and you can tell me why I am wrong. :)

First I want tell you what kind of greenhouse I am looking at building. It seems that the PVC hoop system with a poly covering is probably the most economic way for us to build a greenhouse. I have found a design that I really like that incorporates 6 foot long pieces of re-bar driven 2 feet into the ground that the PVC pipe slips over. This method results in the hoops being vertically straight for about four feet before arching over and provides more head room. The structure is the easy part. Using this system I can build a 20' by 15' greenhouse structure for around $100. What to cover it with is not so easy of a question. My first thought is to simply cover it with 6 mil painters plastic that you can buy at Lowes in long rolls. My reasons? It is cheap, readily available and easily replaceable if it should get damaged by a wind storm (we do get those here in Texas) or deteriorated with age. I know there are much better coverings, but unless there is a scientific reason like, it blocks necessary UV rays, or it releases chemicals that are harmful to plant growth or something like that, I see no reason why it cannot be used. My biggest fear is that I will spend hundreds of dollars on a material to cover my hundred dollar structure, only to watch the first wind storm shred it.

So I guess my first question is; is there any reason 6 Mil Clear Polyethylene Sheeting should not be used to cover my greenhouse structure, or is there a better sheathing that I should choose that would be in a similar price range?

Question 2. Winter Cold

For most people this is the killer for year round production, but for us it is not because of a special arrangement with have with a local oil and gas company that provides us with natural gas at no cost. So the question of what type of heat production equipment to use is solved for us, but I still have some concerns about proper implementation of natural gas heaters. My first question is whether I should use vented or non vented gas heaters. Vented types will dry the air out; where as non-vented will created higher humidity levels. Humidity is good, but if it is too high it can lead to fungus and mold growth. Also gas heaters produce carbon monoxide I would also hate walk into my green house and die of carbon monoxide poisoning. My thought is that I could probably find a couple of used vented wall furnaces on craigslist for little cost. Do you see a problem with using vented wall furnaces? What would you recommend? Another question regarding this same issue is heat retention. I know I need to provide circulation. I could either use some ceiling fans or box fans for this. But it is going to be really hard to not get some cold spots with 6 mil plastic walls when it is 14 degrees outside (Yes it gets cold here in Texas too). My thought here is that if the answer to my first question above about using cheap 6 Mil Clear Polyethylene Sheeting is that it is okay, then it would be cheap enough for me to build an over structure that would give me about a one foot space between the two structures. If sealed properly this would give me a one foot dead air space which would dramatically reduce heat energy loss in the winter and lessen the possibly of cold spots. What do you think about that and do you see any possible detriments to plant growth because of this double layer of poly?

Question #3. Summer heat.

Summer heat is a big problem here. It gets hot, really hot! This year was my first successful summer garden and that was only because I used the old native American technique of planting my garden in between rows of sparsely planted corn. The corn provided natural shading and helped preserve ground moisture. My first thought is to cover the structure with black shade cloth. We have a chicken flock and we built a shaded area for them with shade cloth and it is one of the naturally coolest places we have even on really hot days. But how would it work for a greenhouse? Would it reduce the light too much? Is there something better that does not cost a fortune? The shade cloth on our chicken shade is four years old and it has been the most wind resistant material we have seen. If we could cover our GH structure with it, it sure would make the whole thing a lot more wind resistant. I have seen it sold with a % rating, like 50%, 60%, etc. If you think it could be used to help reduce the summer heat factor in the greenhouse, what percent shading factor do you think would be the best here in Hot, Bright and Sunny Texas?

Question #4. Humidity Levels.

What is the best humidity level range to keep my GH at for the broadest range plants? And the same question goes for temperature? What about ventilation? Should I keep my green house as sealed as possible so I can control temperature and humidity levels, or do I need to provide ventilation to the outside? It is usually pretty dry here where I am at. If humidity levels cannot be naturally maintained in the greenhouse, what should I use to increase them if necessary? Could I not use a simple humidifier or vaporizer like you can buy at Wallyworld?

Question #5 Planting method

This is probably the most complicated question for me because there are so many variables that I don't know of when it comes to growing things. I am not the green thumb of the family, if you know what I mean. I have always wanted to be good at growing stuff like I am about building stuff, but I have not experienced a great deal of success in this area. If I did things the way my first instincts tell me to, I would simply dig out the place where I am going to build the greenhouse a couple feet deep (using a backhoe), fill it with a perfectly balanced soil mixture and build the greenhouse over it. Then I would plant straight in the ground. But something inside me says that may not be the best way to do this for reasons I don't know. That's why I need your advice. Are pots better? If so, what size for what plant? Also, if vegetable plants never get killed by frost, will they just keep producing or will they die at some point regardless? If they will just keep on living, if they are in pots, how do you keep their limited soil nutrient rich without have to replace the soil which would cause root damage? See what I mean, it gets complicated. Another question that arises if growing in pots is best; what type of pots (special or will 5 gal buckets do) and should they be on raised tables or on the ground?

Question #6 Irrigation

I have learned through my research that greenhouse plants need to be watered with warm water and not cold water. My eco friendly plan to achieve this is to paint a couple of 50 gallon barrels black, fill them with water and run multiple coils of black poly tubing through them. My thinking is that that the black barrels will gather solar energy to heat the water and that as the cold well water runs through the black poly coils inside the barrels it will absorb the heat warming the water to nominal temperature. I am pretty sure this will work if I use some type of drip system that does not require a high volume of water. This leads me to me the next question of what type of irrigation system to use? Should use a type that delivers water to the base of the plant like a drip system or that sprinkles the water from above over the leaves? Our well water is very hard and tends to leave mineral deposit (mostly calcium) on the leaves of plants. Is this detrimental to plants?

Sorry for writing a book. Hope you all can make sense of it all. Thanks again for your help.

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