Greenhouse upgrade

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Smoke Blower
Original poster
Jun 12, 2011
Port Townsend, Washington
I have a 10x20 GH that I built using a  Costco shelter frame covered with 7 mil  GH plastic film. I have planting beds raised to about hip high. I have used it to grow tomatoes for the last 2 years. I am now interested in growing some winter vegetables.  I have buried Heat tape in the beds 1 pass in each bed. but have no other aux heat at this time. I am on the Olympic peninsula in Washington state. and winters tend to be mild but there is not a lot of sun. I saw a reference to installing a double roof in a poly GH on a previous thread. It would help if I had a diagram. Also Aux. Lighting might help. any suggestions??.

Lathrop, evening.... Dave here in Omak.... I have thought about a greenhouse quite a bit... trying to build something insulated (double or triple layer) and keep it inexpensive is on my to-do list.....
The one thing that pops up continually is separating multiple layers of some type of poly film...

I keep thinking about 1" foam insulation strips in a box pattern... like an old style window.... have the boxes about 12" square... glued to the bottom layer of film with silicone or some compatible type glue.... then place the second layer over the spacers... maybe glue the second layer to the foam also... I know glue/silicone could be a problem in that it may dissolve the film or the insulation... At least with a pattern in that configuration, the "dead air space" could be maintained at least at a minimum level...

About winter veggies.... I have read, in ground growing works better than on tables... now tables with heat is a different animal... that could work really well...
If you choose thermal mass heat storage, like black plastic water barrels, consider in barrel water heaters... just to keep ice from forming and a secondary heat source for the greenhouse..

It would be so nice to have fresh veggies in the winter.... and have your garden plants with a 2 month head start in the spring....

There are many gardeners on here that should have some ideas to help you out.....
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Thanks Dave,  I  did read a post referring to using an air pump to keep the layers separated which also allows air exchange. I don't want to reinvent something that may already have good cheap solutions.

My GH gathers moisture which in turn reduces the amount of light which is already at a low ebb this time of the year. .Venting helps but at the expense of air temps.  I can imagine using a heat exchange scheme to get around the problem but it will require an investment in time and money.. so i am interested in how others have dealt with the many design problems for growing vegetables in  the winter. 

 I have been looking at Grow lights on The Internet. Most of what I see refers to inside growing. usually Pot. So Mercury Vapor lights ar thought to be ineffective and produce too much heat. However as an adjunct to natural light and where additional heat is desirable can  they be effective?

 My beds are not on tables per se. but are raised planter boxes.  most  of my GH is constructed of recycled or surplus materials. Even the industrial heat tape  was acquired at scrap price.  The GH poly Film came off the internet at a much lower price than the local garden store is asking.  The Steel Costco frame was free.  My Solar exposure is less than ideal as I live in the woods and have only a few hours of direct sun each day + a climate which has many grey days.  

 Just talking with you helps me to formulate solutions and identify problems. So thanks for the conversation to date. It is helpful.

I have heard about the new LED's they are making to produce light similar to that of the sun's rays.... Expensive but almost nothing to operate... the light spectrum was the difficult part to duplicate... If you need more sunlight, reflective material strategically place in areas of the greenhouse where plants were not growing could redirect the light to the plants... something to consider...
I have heard about the new LED's they are making to produce light similar to that of the sun's rays.... Expensive but almost nothing to operate... the light spectrum was the difficult part to duplicate... If you need more sunlight, reflective material strategically place in areas of the greenhouse where plants were not growing could redirect the light to the plants... something to consider...
I agree as to reflective material. I have some on my wish list on amazon. as to LED's my impression is you would need to put then very close to the plants.  Still a pit pricey.  One objection to MV was if they were close enough to make much difference they would burn the plants. Spectrum is part of it and intensity of the right wave lengths are another. ie x wave length at Y intensity at Z distance. I do not have enough information or experience to Know quite what to do. I am considering buying a digital ballast that will do both Halide and HPS. bulbs. I have a large heavy fixture that was used to light the working deck af a Seine boat. very high quality. It was a mercury light. The Ballast was 450V so not useful. However it is a really nice reflector. I also have a MV yard light that will put out  a lot of lumens. I can but MV bulbs that have a shifted wave length. lots of choices not much money. so I am still gathering informatiom.


You want to have an air gap between two sheets of plastic?  How about inserting sheets or strips of bubble wrap? It lets the light through while maintaining it's shape. It should be relatively inexpensive/wrapped in it. You could even use old pieces of used wrap from any company that gets stuff shipped in it. That would save them from having to dispose of it so they'd probably let you have it for free.
Interesting Ideas  for insulation..   One could test them out on cord frames befoer attempting a larger project.  My attempt to grow lettuces last winter was a failure. I  just planted seeds in the fall and then left for a month.  some friends came by every few days and watered. There was some cold weather around thanksgiving and the seeds sprouted but then went dormant. I gave up and dug them in last month.  They were alive but not growing. The grass on my lawn is now growing after being dormant for several months so I guess its time to start planting again.

Check out Johny"s selected seeds site.  I forget where exactly by there is a very interesting video of a lecture from a guy that gardens over the winter in Vermont or New Hampshire.  Tells how and what he is doing.  Sells his produce to the local stores and gets a couple crops each year.
My last post was some time ago. right now I have Several sorts of tomato plants. peppers. an eggplant. and Garlic + some herbs and greens in the Green House. Our outside Gardens have pretty much a full range of stuff. I Am interested in doing some productive growing in the Green house in the winter. Our winters tend to be quite mild in terms of temps. Never below 0* F. However I do not have a good S exposure and live in the woods. so light in mid winter is a limited. I did pick up a 1000 watt grow light which I will deploy next winter. However even tho we are ate the sme latitude as N. Main we have relative ly warm wet winters with little snow.  We have some stuff growing outdoors even mid winter. kale. leeks and Chard come to mind.

 thanks for the post.

I do have the materials to do a double skin on the G.H. Right now I will probably deploy some shade cloth as temps get to high in the daytime and my fans can barely keep pace. .
I am Moving t a new location. a house with a 10K sq.ft. lot. + a garage with a 400' sq.

ft guest house. The /frame has been moved. The rest of setting up  the GH is a relativly  low priority..  

However I have changed the design by adding some windows along the side and putting

along the lower 2 or 3' depending on the size of the windows which were free. So the GH plastic sheeting will

only cover the top portion. I have excellent S. exposure in the new location. It is too late for tomato this year.

I Have some outdoor plants but no ripe fruit as yet.
I understand taking cuttings from an existing tomato plant will produce much faster than starting from seed.... look up "cloning or grafting" tomatoes on u-tube... mhpgardener has a great site....
Interesting Idea. I have always planted starts. However My gardening partner [we have a shared garden at their house]

started some plants from seed this year and is getting fruit now. This is an extraordinary year in Puget Sound. Hotter and drier 

than any on in my experience. With record Hitemps for the  year.  great for tomato plants grown outside.  a good friend

has a grape vine which is ~ 5 or 6 years old that never  fruited till this year. It has a huge crop. which may well ripen. 
This may be a bit outside of what is being thought about here but a sun pit may be a very inexpensive way to keep a greenhouse through the winter. You do need to dig a 4 foot deep hole but nothing freezes inside and if you can provide enough light into it with some auxiliary heat it might work for growing winter veges. I've had a small 6x4x4 sun pit inside a hoop house for over 20 years where I keep potted plants during the winter and I can tell you nothing freezes on the coldest nights. It's lined with 2x12 lumber and has a clear 45 deg. sloped face. I've seen the frost creep down the side of the pit during extended low double and single digit times. Not sure if this helps any. I'm sure it will take some digging (small bobcat) to get a reasonable size to grow veges in any quantity. Good luck with growing during the winter.
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