Instructables

Building and Improving the Harbor Freight 6x8 Greenhouse

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The 6x8 Harbor Freight greenhouse kit can be a true bargain with its $299 price tag and an always-available 20% off coupon making it the least expensive aluminum framed/polycarbonate paneled unit on the market.   But the entry level cost brings with it some challenges which are well documented on a number of gardening sites.   These challenges include:

1) Owners report premature deterioration of the polycarbonate clear plastic panels in hot/sunny climates such as Zone 9a where I live.   Harbor Freight claims the panels have UV protection but many owners have questioned this assertion based on rapid discoloration, brittleness and pitting of the panels.

2) The aluminum frame pieces are thin and the unit is flimsy and unstable during construction making it very difficult to assemble by just one person.   Even when finished, the unit is somewhat flexible and susceptible to damage in light and moderate wind or rain.   The manufacturer even stipulates the unit should be erected only in areas “sheltered from the wind”.

3) The 6x8 unit has minimal headroom inside (approximately 6' at the peak) and the doorway is just 5'4" tall making it difficult or uncomfortable to enter and exit.

4) The unit comes with a sliding door rather than a hinged door.  Owners complain the slide mechanism often jambs and that the door can be blown off the tracks in light to moderate winds.

This Instructable demonstrates how these problems can be reduced or eliminated by:

1) Covering the questionable polycarbonate panels with high quality UV protected 6 mil plastic film. (Cost approximately $60)

2) Building a rigid 2x4 framework of benches and shelving which doubles as a solid interior structure for anchoring the aluminum framework during construction and for providing ongoing stability.  (No additional cost assuming benches and shelves are already planned.)

3) “Raising the Roof” of the HF unit nearly a foot by using 2x12's set on edge for the greenhouse’s base.   (Little or no additional cost compared with alternative “foundation” systems described in the construction manual.)

4) Reconfiguring the stock door so that it is solidly hinged to the framework rather than operated as a flimsy slider.  (Cost approximately $20 for hinges, latches and weatherstripping.)

The tools and materials needed for these improvements will be identified in the individual steps which follow.   One cautionary note, the assembly instructions which come with the HF greenhouse are notoriously difficult to follow.  The good news is there are a number of owners on the web who have documented their builds and provided helpful tips for deciphering the directions.   With just a bit of searching around you will be able to locate these references and eliminate a lot of frustration during the assembly.

One other consideration to keep in mind.  In addition to the additional $80-$90 in cost for upgrading your HF unit, these improvements are somewhat time consuming, particularly the application of UV resistant film to each polycarbonate panel.  I would estimate that at least 16 to 20 additional hours are needed to build the unit as described below versus erecting the unit in stock fashion.   For some people it may be worth it to step up to a more expensive greenhouse kit that includes panels with established UV protection.  
 
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RadyStefanov3 months ago

Hi Dewey,

First, thank you for your article, I took most of your ideas in building my greenhouse, and I love it.

I also saw how you use shade cloth to protect from the heat. Can you tell how well does the shade work, or maybe it does not? Did you remove the panels completely before putting the shade cloth? Do you think it is important that shade cloth goes all the way down to the wood? I placed some shade cloth and removed most side panels, but there is not enough ventilation, so the temperature inside gets higher than outside. Trying to figure out how to deal with the Texas heat.

One more question. Have you thought about updating your article, after all this time? Perhaps there are new ideas you can share, or things that, looking back, you could have done differently?

dewey302 (author)  RadyStefanov3 months ago

In my opinion, the shade cloth does a terrific job. My guess is your Texas heat might be similar to here in the CA Central Valley. Even in the middle of winter, the sun can get very intense. So I leave my shade cloth on year round. My seedlings do pretty well in that amount of shade even in the late winter/early spring. And during the summer it is a necessity unless I opted to put in a lot of expensive fans and vents. My inside temps do go above outside temps but NOT outside temps in the direct sun. My feeling is the ambient temp is not the killer...it's the temperature in the direct sun that will do in the plants.

During the spring, summer and fall I have the door open at all times and I remove the panel on the wall opposite the door. I also totally remove the two roof vent panels. I keep all the other panels in place. I wouldn't think the shade cloth needs to go down all the way to the wood unless you have low plants sitting down there at floor level. If you can, I'd cover all the way to the wood. But not absolutely necessary.

Your suggestion of updating the original article is a good one. There have been some good questions and suggestions in the comments section and some minor changes I have made (like the shade cloth) that more readers would see if I summarized them in the original. Now I just need the time to do the re-write.

Dewey

ablue55 months ago
Hello Dewey,
I have 3 questions. Would you recommend using composite wood rather than red cedar to keep rotting to a minimum?

Did you have a system in play for automatic watering or misting?

Did you have lighting.. fans or heat/cooling?
dewey302 (author)  ablue55 months ago

I used treated lumber for the base and shelving supports. I'm no expert, but I would think composite wood might be the least preferable choice due to potential rotting and glue failure resulting from high temperature fluctuations and possible UV rays. Cedar would be a nice choice but might be pricey depending on your location.

I don't have any automated watering or misting. I do both by hand. I have a wide variety of plants (from tiny seedlings to full size lettuce) at any one time and I move plants in and out almost daily depending on their size and maturity. I also shuffle them around on the shelves depending on their light requirements. So an automated watering system would be a challenge for me unless each drip/feed hose had an individual valve to regulate the water flow to the various plants that would be in any particular position in the greenhouse. But an automated misting system would be a very nice addition since all my plants could use a spritzing now and then.

I don't have inside lights but it just so happens I built my greenhouse about 5 feet from our cabana, and the cabana has a number of perimeter lights which provide more than adequate illumination if I want to work after dark. Also keep in mind, your local building code may require you to obtain a building permit if you install electricity or running water inside your greenhouse (ours does). And in some localities, that can be a major headache. I also do not use fans or mechanized cooling. As I noted in another post (including a photo) I keep my greenhouse covered with shade cloth year round. I also remove the window panel opposite the door during the summer and I keep the door open as well. I also remove the two roof windows during summer months. For the simple flowers, trees, bushes and veggies I grow, this seems to provide adequate growing temperatures in spite of the intense heat/sun here in the Central Valley of CA. BTW, I also don't heat during winter months. We do get frost here, so I'm still learning which plants will survive and which won't. For my really early seed starts...I do everything in our house under grow lights.

waterstar8 months ago

Excellent post. Also like your post on the sliding barn doors. THANKS.

Can I make the greenhouse 2 feet taller by using another type support?

dewey302 (author)  waterstar8 months ago

I would think so but I've never tried it so I don't know what complications you might encounter. You might have to reconfigure the door a bit to reduce its overall height to 7' or less otherwise it might get a little floppy. Keep in mind the aluminum framework with the kit is very thin and light so any structural support you can incorporate into your design is going to be a real plus.

Hi Dewey, appreciate your 'ible here!

I had one of these gifted to me, I'd been toying with buying one for quite a while. I have a pre-existing 10' x 12' level concrete pad (it had another structure on it) - I'm contemplating using stacked concrete blocks to raise it up 16" around the perimeter of the greenhouse frame. Concrete block for me would come out to ~$65, versus double that for 2x12 treated lumber. I'm considering leaving the door intact, a 16" step-over height for me wouldn't be the end of the world, and gives me a cooler zone down at the bottom. I could, of course, cut the block, but if I leave the frame intact, it'd probably make it a bit simpler to disassemble the next time I (ick!) move.

Anyway - it's sitting in its carton out back on the pad, I'm overwhelmingly tempted to go put it together, but I really should wait until I can borrow a friend's truck and go get some block.

Appreciate any thoughts you might have!

-A

dewey302 (author)  adrenalynn6 months ago

In figuring your costs (block vs treated lumber) be sure you include a "sill plate" if using blocks. You need to have a way to secure the greenhouse frame to a sill plate and then secure the sill plate to the blocks. Or in the alternative, you need a means to secure the frame directly to the block.

Regarding the "step over" entry door I guess this comes down to personal taste and your willingness to put up with stepping over the blocks each time you enter or exit. I know I would get frustrated with a step like that very quickly. But then that's me. Just give it a good long "think" before you go that route.

BTW - I envy you getting one of these as a gift. Should be fun.

Hi Dewey, thank you for your considered and quick reply!

"When I have money, I don't have time. When I have time, I don't have money" - story of my life. I'm in one of those crossing cycles at the moment. ;-) My projects tend to outgrow my [non-existent] budget entirely too quickly.

Our weather is pretty mild here (Sacramento, CA), some strong winds rarely in the winter, but I'm pretty insulated in that small back yard w/8' plank fence.

My plan was to lag a small piece of 2x4 scrap inside the block every couple feet, then screw the frame directly down to it. If the greenhouse still lifts, it's probably sited wrong at that point, since there's nothing for the wind to "get under".

Step-over: you may end-up correct, fortunately that's one I can remedy at any later time. Angle grinder will cheerfully cut that block as well as the aluminum sill, so that leaves me time to reengineer the door at my leisure. The big thing is to get it up and planted before the season gets much later. Not raising the house now is something that's difficult to correct in the future after it's constructed - if that makes sense.

I do the odd electrical engineering work, and sent my client to HF to pick up a few bits for the job I was doing for them. They know I've been coveting that little greenhouse since before moving into this house, and they picked it up for me as something of a "tip". Very considerate! They even dropped it off at my house and helped me carry it back to the pad.

16" lift (rather than 12" 'nominal') feels more like what I'd want, as I really want to play with hydroponic lettuce and other leafy growing, and vertical density is important to me.

Anyway - I do really appreciate your input, and that you took the time to put this 'ible together! Thank you so much again!

dewey302 (author)  adrenalynn6 months ago

Adrenalynn,

I'm not too far down the road from you...in Merced/Atwater. Being in the Central Valley I think you might want to plan on one further addition to you greenhouse. Shade. I keep my greenhouse covered with shade material (comes in rolls at HF or Lowes) year round. I discovered (sadly) very early that the intense sunlight here in the valley can toast your plants in no time flat. I have attached the shade cloth with simple plastic clamps that I buy by the dozens in bags at HF or other big box stores. I also keep the door open permanently from about March-October and remove the center panel on the opposite end from the door during those same months to provide more natural air movement through the "shadehouse". I've attached photos of the outside and inside of the greenhouse showing the shade cloth attached.

007.JPG003.JPG

Here's the site, as-seen by one of my cctv cameras. Notice the pad at the far end of the photo (with a set of ladder legs on it, and the Harbor Freight box laying across it).

greenhouse-site.jpg

Thank you again, Dewey!

I'm sited under a large Live Oak. I get about 4hrs in the early morning and 3 hours in the evening of sun there in the summer, but it's wide open in the winter. Door is to the south. I have a couple of shade sails that I figured I'd take from the oak to the ground on each east/west side, so I can roll them up and down - maybe even automate.

Your work is so pretty and clean! I'm impressed with the craftsmanship and preplanning. Wire Shelving is "ClosetMaid" isn't it? I built that out in my closet (shoeeees!) a few years ago, looks familiar. :)

After our discussion, and rereading your 'ible here, I got to thinking that I might drive strongties into the pad, bring the 2x4's up at the frame up rights through the cinderblock (as previously discussed) and then dump some quickcrete into the block. That would tie the 2x4 to the pad, and stabilize it through the block, and then I could just lath-screw the whole frame to the 2x's. Incremental cost is negligible that way.

Have you considered a mister in there? I was contemplating tossing together a 1/2" mister running the entire length at the frame peak, front-to-back. (we get pretty dry here in the summer, as do you, and that airflow you describe through the mist would definitely help the plants "sweat" instead of broil)

I had also been contemplating a box fan in a custom panel at the front and back.

Have you managed to extend your growing season to year-round?

Thanks again for the chat!

waterstar7 months ago

Where did you find the " high quality UV protected 6 mil plastic film. (Cost approximately $60)"?

dewey302 (author)  waterstar7 months ago

Details regarding the UV film can be found in Step 6 of the Instructable. As noted there, I got mine on line from the Greenhouse Megastore.

Thank you. Also, is there a reason the ceiling/roof does not be covered or did you do that and I misunderstand?

dewey302 (author)  waterstar6 months ago

As noted at the very beginning of step 6, ALL panels are covered with the UV film EXCEPT the four panels that make up the north wall of the unit. So yes, the roof is covered. Sorry if that wasn't clear.

Ok, that makes sense. Thanks so much for all of your time and patience.

pampero6 months ago

Thanks> good!!!!

waterstar7 months ago
Thanks~

Thank you so much for posting this. I'm hoping to get my greenhouse in a couple weeks but living in central will have to wait some time before we thaw out to assemble it. We've had a nasty winter this year and our summers usually are quite hot and a few tornadoes too. lol

I've always been pretty good a assembling things but nothing of this scale so i'm quite scared actually. But I knew from the reviews that this would need some strengthening. Am wondering though can I still do the shelving without raising the greenhouse?

I'm hoping to get a parts list together for the lumber, shelving and hardware together in the next couple weeks. Thanks, Cindy

dewey302 (author)  cjankauski-clemmens8 months ago

You can put shelving in without raising the entire unit. You should be able to design it so that it will attach to and strengthen the aluminum framework. Have fun with your build.

Thanks :)

dboling9 months ago

I've had my Harbor Freight 6 x 8 greenhouse since spring 2013. I found a super saver coupon online and it cost me 199.00. I picked it up at Harbor Freight to save on the very high shipping cost.

Anyway I found for the price, this greenhouse is awesome. I have not made any modifications to it as of yet.

If you take your time with the assembly, the greenhouse is very very sturdy and will withstand some very high winds. Mine has been through around 50 mph +- winds, 1 to 1 1/2 feet of snow and not one problem, ( Knock on wood ).

Besides having a nice square base, the trick to assembly is to not fully tighten the bolts until the side panels and door are mounted on the frame. Start tightening the bolts on the door side, while squaring the greenhouse frame to the door. Make sure you pull the pieces that your tightening against each other. Use a 1/4" drive socket to tighten the bolts, not the cheap wrenches that are supplied with the greenhouse. Last insert the roof panels while squaring the roof frame and tightening the bolts.

I do have few modifications I plan to do:

Strengthen the roof vents. Add a light weight 4' florescent light in the middle of the ceiling and add some shelving.

After 2 days searching the internet for shelving, these are my final choices.

http://www.amazon.com/Flower-House-FHSP300SHV-SpringHouse-Economy/dp/B001TI045S/ref=cm_cd_ql_qh_dp_i

http://www.littlegreenhouse.com/accessory/bench.shtml

I'm also thinking about purchasing a 2nd 6 x 8 Harbor Freight greenhouse so I can bolt it to my current greenhouse to make it 6 x 16 with doors on both ends.

I like dewey302 modifications above. Covering the panels sounds like a great idea to protect them. I'm in zone 5 -6 so I might not need to cover my panels.

P5080328.JPGP5060283.JPG
bakdrft9 months ago
I wonder why you purchased this greenhouse knowing that there was so "many" things wrong with it? Did you do your homewaork before buying it? I would think that you could have spent 300.00 on wood and glass and built a larger house.
dewey302 (author)  bakdrft9 months ago
If you think you can build a 6x8 greenhouse of glass and wood for $300 by all means do it and post it up here on Instructables along with your detailed budget and materials list. That is what the site is all about. Showing what you've done so others can improve on the ideas.

Did I do my homework? Well probably not to your standards. Around here single strength glazing, cut to size, is 1.8 cents a square inch (True Value Hardware quote). The panels for a 6x8 greenhouse would have been $497.73. The treated 2x4s for the basic structure would have been $73.69. There would also be the materials cost for attaching the glass panels to the wooden framework - which I didn't calculate since the cost was already well beyond what I intended to spend on the HF unit.
Joan16chickens10 months ago
Thanks so much for quick response. Sorry this is my first time looking for online help and I did not see the box to click on for the Step by Step instructions. All is explained there very clearly and with excellent illustrations. Appreciate your sharing.
Joan16chickens10 months ago


Joan16chickens says: 0 seconds agoReply

Covering the questionable polycarbonate panels with high quality UV protected 6 mil plastic film. (Cost approximately $60)
Can you please explain this better for me? I have some 6 mil UV protected film and was wondering how to I attach this to polycarbonate panels? OR what type of UV film do I use/where purchase? Do I put it on the interior of the panels and tape it down to the panel?
Thanks for helpful comments on putting together greenhouse.
dewey302 (author)  Joan16chickens10 months ago
Hi Joan.

Go to step 6 of the Instructable and it will show how I attached the UV film to the panels. There may be better ways of doing it...but this is how I did it and things have held together thus far. Be sure you put the film on the outside of the panel. This is what blocks the suns rays from deteriorating your polycarbonate.

Dewey
Dr.Bill1 year ago
I find most of Harbor Freight stuff needs a little extra engineering to make it work right.
This little green house looks pretty good.
amazing
mrmacray1 year ago
well done!
pamelamilo1 year ago
Love it you did a really nice job I would like to have one I have the ideal spot for one but it would have to be a custome fit would like to attach it to my sun porch the room is heated in the winter we live in zone #5.
take care
Pamela
pamelamilo1 year ago
I really like the uv film I think my 2 felines would think that was for them to enter and exit so hows it all going do you love your new green house?
jleslie481 year ago
excellent tutorial on beefing up the greenhouse.   I've done similar, and its up almost a year now, and all is fine;  and that includes surviving hurricane sandy.   I found the 2x12's to be almost the same price as 4 2x4's, so I used that as my base instead. so instead of rising 11.25" (nominal 2x12) I was up 14" (4x 3.5 nominal 2x4)   This also has the added benefit as I alternated the grain on the 2x4's so it can't bow/warp (one 2x4 bowing is pulled straight by the other 2x4 bowing in the other direction)   Home depot also has a culled wood section which if you check regularly, has some amazing pieces of wood in it for $0.50.   I was able to pick up some 24 2x6x4' section, so for $12 I had my 4 tables: 

http://jleslie48.com/jl/120524_house/ap404.jpg

http://jleslie48.com/jl/120417_greenhouse/Dsc00358.jpg





ap404.jpgDsc00358.jpg
dewey302 (author)  jleslie481 year ago
Thanks jleslie. And great job on your greenhouse. Looks terrific.
People bad mouth and complain about the HF's greenhouse, but I think they are unrealisitc about what it is. If you go in knowing its very cheap and flimsy, and take that into consideration, you can build it up quite nicely. I could tell right away that the aluminum framing was the bare minimum to just hold the uv panels in place, so If I wanted it to survive in a wind, I knew full well it was going to need more.

Plus I think a lot of folks think that aluminum framing is like a scaffold frame, where you can hang stuff off of it. No way!!!! The fact remains, I got mine for $249, added about $150 worth of wood, deck screws, electrical boxes, and a water line, and I ended up with a first class greenhouse, with a full set of benchtops. You can't touch any greenhouse from a "regular" supplier for less than $1000, and thats bare bones: no shelves, water, or electricity.
Lorddrake1 year ago
Fantastic job making a silk purse out of a sow's ear.

I love to shop at harbor freight, I just have to keep reminding myself .. you get what you pay for.
dewey302 (author)  Lorddrake1 year ago
Thanks Lorddrake. And you are right about shopping at HF. I use it often for buying and trying out entry level tools and products. If I find the tool useful and needed on lots of occasions, I'll step up and invest in something better. A good many of their tools are quite adequate for intermittent hobbyist use.
I'm glad i'm not the only one that uses HF for experimenting with tools before investing in a pricey better quality version hehe.

one thing I love to get from there is the bar clamps when they go on sale for $1.99.