Strawbale cold frame

[bennelson]

Hi everyone,

Recently, I tested some old seeds to see if they would germinate or not. Then I foolishly planted those seeds in a seedling tray.



I know... what was I thinking?

Now I will need some place for those seedlings to go, but of course it is still way too cold outside.

Perhaps some sort of cold frame?

First thing I did was shovel some of the snow out of the way.


Fortunately, most of the snow has melted. It was 3 feet deep here last week.

Next, I hit up Craigslist to find who was selling straw bales, and then went to pick up a load of them. This is the kind of situation it's nice to have a pickup truck for!



All I really did was measure out the size of scrap greenhouse glazing I had, and then start laying straw bales on the ground to match that size.






Once I had the ring of bales, I just flopped the glazing on top. Since I had a couple spare bales, I set them on top in the back, where they won't block the sun, but they will keep the wind from moving the glazing.

If the glazing was angled to go up to the "second-story" bales, it would be a better sun angle for this time of year. I would need to fabricate some sort of side walls though.

Perhaps a simple wooden frame, which would set ON the bales, and cover the ends?

I'll let this sit in the sun for a few days and see how it warms up. Ooo! That reminds me, I need to get a thermometer to put in there...

[RobertSmalls]

Just a few thoughts come to mind.

The colder your plants are, the slower they'll grow. At this point, colder = better. Move them to the attic or porch?

Once you've laid down the bottom layer of straw bales, you're not going to gain any additional solar area no matter what you stack on top (exception: mirrors).

Which reminds me, don't you have a stack of old plastic mirrors? Perhaps it's time to build a solar oven for your garden.

There's one thing I learned the hard way is it's much better to throw out seedlings than it is to plant them too close together.

Good luck!

[bennelson]

There is not accessible attic space in my house.
The back porch is completely open. It's just the outdoors with a roof overhead for shade, so neither of those two things work.

For stacking the bales, I was referring to just the back wall, so that the glazing is angled. That makes is more square on to the elevation of the sun.

I DO still have some mirrors around. (I donated most of them to a Burning Man project.) They would be too tall for the back wall of a single bale, but would fit vertically on a two-high bale back wall.

I'm also hoping that I can container-garden some of these seedlings as well.

[basjoos]

You might want to add some water filled containers (gallon milk jugs) for heat storage inside the cold frame and place them around any especially cold sensitive seedlings. Another way to improve nightly heat retention is to place vertical glazing on the southe side and have insulation with heat reflective foil (foamboard) on the inside of the roof covering. Those bean and tomato seedlings in your photo can't take any below freezing temps.

[bennelson]

I saw the "Wall o Water" at the local garden store. I thought maybe a homebrew (inexpensive) version of that might be a good idea.

I wonder if dark-colored plastic jugs of water would be better at absorbing and releasing heat.


I also did just scrounge up some free radiant barrier material. It was used as a shipping/packing material - bubble wrap with a silver aluminum finish on the one side. I thought that might make a good "north wall" material.

More things to try experimenting with!

[bennelson]

In my travels today, I stopped at my favorite materials salvage facility. (A dumpster with a friendly owner, my father. Whatever I pull out of the dumpster is less materials they have to pay for to remove!)

In the dumpster, I found 3 dual-pane storm windows with wood frames, and some chipboard with 1x2" wood screwed to the edge, which was part of a shipping crate.



Look at that in the back of my truck - it looks like something I would have spent money on!

The windows had screens on the one pane. I had to bend/kink them to get them out, as they were "built-in". They had to come out as screens provide a fair amount of shading.

I didn't notice it, but one of the windows is a little taller than the rest.

I put the windows over the top of the bales to see how it looks.


The three windows together are not quite as wide as the poly cover I had, but the glass is much more clear than the plastic as well.

Here's the same windows propped up onto the second story of bales.



I should be able to use the two sheets of chipboard to make triangular ends and some sort of front and rear base for the windows.

I would like to build something similar to this:

Only it would be larger, and the back wall would be straw.
(Check out the builders blog at ONE STRAW.)
Here's another great photo of that same cold frame.


That's made by the same guy who I was recently helping build a 8' tall arched greenhouse.

[bennelson]

We've had a couple of warm days lately. Enough to melt the snow AND get some good sunlight.

It was 35 degrees today. Still above freezing and nice and sunny. I had put my outdoor half of my wireless digital indoor/outdoor thermometer in the strawbale coldframe.

Temperature in my house (on the north windowsill) was 64 and it was almost 55 in the coldframe!


I did still want a slanted top for the cold frame, so I started working on that today. I started with one window, figuring that the ends would be the same no matter what, just the middle would be longer.

I may end up moving all this to a different part of my yard as well. The spot it's in gets great sunlight in the afternoon, but is shaded too much of the morning. Last week, the spot I would have liked to set all this up was under 5' of snow....

I measured the height and length of the window when it was slanted on the second story straw bale. I then cut a pair of triangles that size from the salvaged plywood. Inside was another scrap of wood to support the window. Near the top corner, I put a screw through the end into the window to act as a partial hinge.



Once I had all that worked out, I simply extended it by adding a 1x2 slat the length of all three windows across the upper back. Straw bales still make up the back of the structure.



And here it is from the front.



I still need to add hinges to connect the top of the windows to the upper cross member. This will allow me to prop open any of the windows. I also need to add another cross piece on the bottom (to keep the bottom of the end triangles from spreading out.) I also plan to add battens - as in "batten down the hatches!" - vertical wood strips between the windows. That will help seal between the windows to keep the heat in.

Speaking of plastic mirrors.... I did find that I had a pair of them in my garage, so I put those inside the back of the coldframe as well.

[arcosine]

If you make the inside a dark color, it will reflect less light out the windows.

[bennelson]

The dark color will be the ground itself.

There's not much else that I can easily change the color of. (Not going to paint the strawbales!)

I was thinking of using some salvaged silvered bubble wrap to line the wood triangular sides.

[Ryland]

How about this for an idea, put the windows near upright, so they are on the front instead of the top of the cold frame, the sun is still really low in the sky even at noon, so if the windows were at the front instead of the top they would let alot more light in and thus heat it up faster, if you have enough windows and bales and another indoor out door thermometer you might try so you can compare the two.