Assembling a Small Greenhouse Kit

We bought a small greenhouse kit to extend our growing season. Here's my review of the assembly process.

Review of a 6x8 Harbor Freight Greenhouse Kit

I've wished for a greenhouse for years. 

Several of my homesteading and gardening friends have homemade greenhouses and hoop houses. I've made notes of each one, of their ingenuity, of the systems they've put into place.

I planned to build my own someday. I've been saving windows and even the glass storm door we replaced on our house. They would form the ends of my little structure, which would be made with cattle panels in an upside-down U shape, covered with greenhouse plastic.

In the meantime - while I collected windows and waited for my home-built greenhouse - I've started seeds indoors

A flat of young tomato seedlings started indoors.

Since our house cats like to munch seedlings and the dogs like to eat my young plants when I put them outside to harden off, I was limited in how much I could do.

I started seeds on the kitchen windowsill until Thor joined our family. He's a sweet cat that was dumped as a kitten in our front yard a few years ago. 

Unfortunately Thor refuses to stay off the kitchen counter no matter what I try, so the windowsill was lost to my seed-starting program.

That left the small bedroom that is my office. A card table in front of the window is all the space I have, and the closed door keeps cats at bay. 

Our 6'x8' greenhouse kit

This 6'x8' greenhouse kit was pretty easy to assemble.

Last year for Mother's Day the Chief surprised me with a greenhouse kit. 

I think he got tired of hearing me talk about my plans, tired of the stack of mismatched windows in the garden, and was worried that my project would be... an eyesore.

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It's a small greenhouse, but it's so much more space than I've ever had before. Dedicated space, where seedling-munching cats can't get into trouble.

He bought a 6-foot by 8-foot Harbor Freight greenhouse kit with an aluminum frame, sliding door and two vents.  

Disclaimer: this is NOT a sponsored post and that is NOT an affiliate link. Harbor Freight has no idea who I am. We bought this kit with our own money, and the opinions herein are our own.

Here in Oklahoma the summers are so very hot that nothing would be able to grow inside this greenhouse, even with the roof vents and the door open, so it's a seasonal solution for starting seeds and letting transplants grow out. 

In other words, for my purpose it doesn't have to be huge. And shelves will multiply the usable space inside.

How are greenhouses and hoop houses different?

Technically, a greenhouse is a large structure with heating and cooling systems, vents and possibly fans. They are designed for year-round growing.

A hoop house is usually built over bare ground, made of pipe frames set into the ground and covered with greenhouse-grade plastic sheeting. 

Instead of regulating the inside temperature with heat and cooling systems, the plastic sides of a hoop house are rolled up or even removed during warm weather. Crops are usually planted in the ground inside the hoop house.

By these definitions, my little "greenhouse" isn't technically a greenhouse but it also isn't a hoop house. Maybe it would be better called a freestanding sunroom. 

I plan to use passive solar heating to keep the inside warm in cool weather instead of a high-tech heating and cooling system. We'll talk more about that later.

Building the base for the greenhouse

The kit included directions to build a base that the greenhouse sits on, but the kit doesn't include the materials.

The photo of the finished greenhouse at the Harbor Freight website shows the structure sitting flat on someone's lawn without a base. I find that amusing - the grass would need to be mowed inside and the structure would, I'm sure, blow away in the first good windstorm. 

So build a base! Anchor your greenhouse well!

We modified the instructions for the base a bit. Concrete or gravel inside a wooden frame of 6x6's is recommended. 

We used bricks for the floor of our prefab greenhouse.

We used bricks inside the wooden frame of the base because we have a lot of them, leftover from the floor of an old garage we tore down many years ago. 

The bricks are also part of my passive solar heating plans. Concrete and gravel will do the same thing, so use what's easiest and least expensive for your situation. Our bricks were FREE.

We leveled the space, dug it down a bit and added a layer of sand before placing the bricks inside the wooden frame that we built according to the directions. The greenhouse is screwed into the wooden timbers.

Building the greenhouse frame

I'm not the first customer to say that the directions that come with the greenhouse kit are a bit vague. You'll find many more reviews online, and poor instructions are the biggest complaint.

But the Chief is a construction wizard and got it done. 

Our local-ish Harbor Freight had a small model of this greenhouse inside the store, so he made a trip back to the store and took pictures on his phone that he could refer to while building it.

A man putting together the aluminum framed greenhouse.

The aluminum frame is light and easy to put together. All hardware is included in the box. I helped for part of the building process by holding up the other end of the longer pieces while the Chief screwed the joints together. 

The vent panels were easy to put together. A very simple latching system inside is used to open and close the vents.

The roof structure of the small greenhouse is made of aluminum.

He installed the roof panels in the frame before adding the side panels so he'd have more "room" to work. 

This kit greenhouse could easily be put together in one day, with another day to build the base. In fact, building the base required the most labor. 

Is this greenhouse kit sturdy?

Although the greenhouse is very light, once we put all the polycarbonate panels in the frame and screwed the frame to the base, it's much sturdier than we expected. I'm pleased with that.

One of the roof vents of the small greenhouse. There is a gap when it is closed.

I do wish the vents were flatter when closed; there is a bit of a gap at the bottom. A better latching system would help. 

The vents have not blown open in the wind though. I'm going to call this gap "ventilation," which is very important in a greenhouse.

One of the roof panels had a curve where it met the side panel when we first put it together, but a few days later that seems to have straightened out as the structure has settled and acclimated to its location.

I'm 5'5" and the peak of the greenhouse is 6 feet high, so I can stand up easily in the middle of it. There will be shelves around the sides so the middle is the only place I could stand up anyway.

Will this greenhouse withstand the wind?

That remains to be seen, but we've had several very windy days without incident, and there hasn't been any "wiggle" when the wind gusts blew through the yard.

And Oklahoma is known for wind. So far, so good.

My tips

When you unbox the kit, be sure to locate the wrench and the special tool included for installing the clips. The special tool was mentioned in the instructions but ours must have disappeared with the packaging into the trash. The Chief modified a screwdriver to do the job.

The open door of the little greenhouse, before the side panels were installed.

The greenhouse door was a little tricky to put together and a bit confusing to install; the instructions could be better. 

I do wish the door would slide more easily, that's my biggest "thing" with this kit. But it doesn't blow around in the wind and is nice and tight to the frame, with good "stops" to keep it from blowing open. 

Maybe some WD-40 will help it slide better?

My plans for the greenhouse

I'm ready to move in! We have two metal shelving units in the mudroom that the Chief has wanted to relocate. I've claimed them and will be moving them to the greenhouse to hold my trays of seedlings. 

We located the greenhouse in the corner of my fenced garden. Yes, it takes up 48 square feet of my garden, but I have a reason.

When I open the greenhouse door on warm days, I don't want my dogs to be able to go inside. Locating the greenhouse inside my garden fence means the dogs (or rabbits or other critters) can't get inside. It's as simple as that.

So when it's time to harden off my little plants before planting them in the garden, I'll move them out of the greenhouse, inside the garden fence. Again, to keep them safe from the dogs. 

For some reason, chewing up young plants is irresistible to our dogs. I've lost enough transplants to know that plants must be kept safe!

I'm also hoping that I can keep potted herb plants alive over the winter inside the greenhouse. I've given up on growing rosemary because it dies every winter, even the ones that I bring indoors. So that might or might not work, but I will try.

Passive solar heating in the greenhouse

I've saved passive heating ideas for years in anticipation of someday having a greenhouse. 

Mine isn't large enough to keep chickens in during the winter (their manure and body heat would help to keep the temperature warmer), or to keep an active compost pile inside (which would use the same principle).

So I'm using the brick floor as a heat sink. It will absorb the sun's heat during the day and release it slowly overnight. 

I may also add empty cat litter jugs painted black and filled with water, which would also act as a heat sink.

Sheets of bubble wrap stuck to the polycarbonate panels is supposed to add another layer of insulation in the winter. I definitely don't have enough bubble wrap, but it's an idea I might try in the future.

While my greenhouse is too far from electricity to do this, keeping a poultry heat lamp turned on at night can also help keep plants warm when it's cold outside. (Don't put the light bulb too close to the plastic panels!)

And next spring? I'll be starting my seeds in the greenhouse at the optimum time for our zone 7b garden. More seeds than I've ever been able to start in the past. I'm excited!

A review of the 6'x8' greenhouse from Harbor Freight.

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