Construction of the cold frame begins with building three identical frames using decking lumber. (I'll provide dimensions and other details on my blog.) Each corner is connected with three 2 1/2" screws. Each frame is not too heavy to carry, but are stacked to make the completed cold frame.
One of the frames is cut on an angle, like this. Each end is cut from the center of the top edge to one inch above the bottom left corner. Then the saw tilt is adjusted to a matching angle, and the long side is cut lengthwise one inch above the bottom edge.
When the smaller part is stacked on the larger part, we get this sloped shape for the top frame. We will show the completion of the top frame later.
The bottom side of the bottom frame is covered with 'hardware cloth' (wire mesh with half-inch spacing), held down with door-stop moulding. The center piece of moulding helps to prevent sagging of the hardware cloth.
Here's a close-up of the door-stop moulding.
A frame is made of 1/2" x 1/2" moulding, and "weed-block" fabric is stretched over and stapelled to this frame. ("Weed-block" fabric is typically used under stone pathways to allow drainage while blocking weeds.) In this case, we want drainage while blocking soil from falling through.
Here the fabric frame is inserted at the bottom of the bottom frame.
Looking from the bottom, you can see the "weed-block" fabric through the hardware cloth.
Here you can see that nine seedling trays fit inside the bottom frame with a little slack.
The niddle frame has a vertical piece fastened in each corner with 1 1/2" screws. These pieces are made of decking planks cut in half lengthwise. Each vertical protrudes one inch above and below the middle frame to lock the middle frame in place on the bottom frame, and the top frame in place on the middle frame.
The outer edges of each end of each vertical is bevelled with a rasp (coarse file) to make it easier to fit the frames together.
Here we see how the vertical in one corner of the middle frame locks onto a corner of the bottom frame.
Along the inside top edge of each short side of the middle frame, a rail is fastened to support the watering system. These rails, and the frame of the watering system, are made of an aluminum extrusion with an L-shaped cross-section, 1" x 1".
Here's the watering frame in place, spray heads down, in the middle frame.
One end of each side rail is cut and bent like this to form half of a hinge.
Two ends of the watering system frame are each slotted like this to form half of a hinge.
When the slotted end of the watering frame is dropped over the turned-up end of the support rail, a hinge is formed like this, that allows the watering frame to pivot at this joint.
Here is the watering frame pivoted up, providing access to the seedling trays.
Here is the watering system, built on a frame made with five lengths of the same aluminum extrusion seen earlier. The frame holds nine spray heads connected by 1/4" tubing to a length of 1/2" tubing. The watering system parts (other than the frame) are from RainDrip irrigation supplies.
From the 1/2" supply tube, nine lengths of 1/4" tubing carries the water to each of the nine spray heads.
This close-up shows the end of the 1/2" supply tube that connects to regular garden hose. Also one of the spray heads is seen here. These are "mister stakes" cut short and inserted in X-shaped holes in the aluminum frame. Each 'mister' head has eight little holes that squirt water in eight directions. The water flow can be individually adjusted for each head.
This shows the end of the 1/2" supply tube that is dead-ended.
Here is a close-up of some of the connections of 1/4" tubing to the 1/2" supply tube.
Where each mister stake comes through the aluminum frame, a small hole is drilled through the plastic stake, and a small nail (or cotter pin) is inserted through this hole to lock the stake in place.
Where 1/4" tubing crosses an aluminum rail, two holes are drilled in the rail and a loop of stiff wire inserted through these holes. Then ...
.. The ends of the wire are twisted to hold the tubing in place.
Here is a close-up of one of the 'misters', or spray heads, and a wire loop that joins two pieces of the aluminum frame.
The dimensions of the watering frame are designed so that each of the nine spray heads is centered over one of the nine seedling trays.
Two ventilation holes are formed in the rear wall of the top frame by notches in the facing edges of the two planks of the rear wall.
Here is a close-up of one of the notches, one inch deep and four inches wide, The bottom of the notch was made by drilling a series of 1/4" holes and finishing with a chisel and file. A 7-inch circular saw was dropped into the center of the edge of the plank 2 1/4" deep to make the thin slot across the notch.
A 3" x 5" rectangle of hardware cloth (with 1/2" wire spacing) is cut for each ventilation hole, and the corners trimmed as shown here.
The piece of hardware cloth is slid into the sawn slot. (First, it is used to scrape sawdust out of the slot.)
When the two rear planks are assembled with facing notches, the hardware cloth is captured in the slot above and the slot below. No fasteners needed!
A vertical piece near each rear corner holds the two rear planks together. These verticals of the top frame rest alongside the rear verticals of the middle frame.
Here is the top frame in place over the middle and bottom frames. The verticals of the top and middle frames work together to lock each rear corner completely.
When the top frame is tilted back, the verticals of the top and middle frames work together as hinges.
I cut a notch in the top edge of the middle frame at the back of the right side for the garden hose that connects to the watering system. But I later moved the notch to the rear wall, because there was less tension when tilting up the watering frame.
Here we see the notch for the hose at top edge of the middle frame at the rear wall, directly behind the connection to the watering system.
A frame of 'stop' moulding is nailed to the top edge of the top frame. Then a plastic window piece is laid on top, cut to overlap only half the width of the 'stop' moulding. Then 'ply cap' moulding is nailed over this to lock the window piece in place, All these mouldings are mitre-cut at the corners.
Looking through the top window, we can see a length of 1/2" x 1/2" moulding fastened to the inside of the front edge of the top frame with two screws. Below that are two pivoting pieces of 1/2" x 1/2" moulding fastened to the inside upper front edge of the middle frame with one screw each. The pivot screws are off-center, so that pointing the short end of the shorter pivot piece upward props the top frame open with a 1-inch gap, and using the longer end of the shorter pivot makes a 2-inch gap. Similarly, using the longer pivot piece provides 3-inch and 4-inch gaps when propping open the top frame.
Here is the top frame propped open four inches.
A larger piece, that can be stowed inside the cold frame, is used here to prop open the top to provide working access.
A second identical prop is used here to hold up the watering frame. Now there is full access to the seedling trays.
For an alternative support for the watering frame, four short rails were fastened to the top frame. This allows the watering frame to be lifted up when the top frame is lifted up and tilted back.
Here is a closeup of one of the short support rails, seen through the window.
With one motion, the top frame, with the window, and the watering frame are lifted together, and only one prop is needed to hold open the cold frame.
The inside of the cold frame was painted black. This increases the heat energy absorbed from the sunligth coming through the window. The seedling trays and the soil in them are also black. If we used any other heat source besides the sun, it would be a 'hot frame'.
Here is a closeup of the mouldings used. On the left is 'ply cap' moulding on top of 'stop' moulding. These are used to frame the window, the edges of which are held in the gap between these mouldings. 'Stop' moulding typically has one rounded corner, but I prefer as little rounding as possible. The moulding on the right is nominally 1/2" by 1/2", but doesn't need to be perfectly square.
Tools needed or suggested for construction of the cold frame include a variety of ways to measure length, a square, and a carpenter's pencil. The yardstick is also used as a straight edge.
A circular saw will do most of the cutting work.
A saber saw will make it easier to cut the bottom of the notches.
The finer teeth of a hacksaw will do a better job of cutting the mouldings. A hacksaw blade is better at cutting the plastic for the window, but the handle gets in the way. The solution is to hold the hacksaw blade with an all-purpose handle (below), which can also be used to hold files.
The two clamps on the left are designed to hold two pieces of moulding or lumber at right angles. (One of these clamps is turned over so you can see both sides.) Clamps like the one at right can manage a wide range of thicknesses.
It is handy to have two cordless drill/drivers, one set up for drilling and the other for screwdriving. It will save a lot of time.
Here we show the 2 1/2 inch and 1 1/2 inch screws used for the project. For each size of screw, choose a drill bit that matches the diameter of the solid core of the screw, for predrilling holes for the screws. Also shown is the 1 1/4 inch nail used for the stop moulding and a thin 1 inch nail used to construct a frame for the 'weed block' fabric out of 1/2" by 1/2" moulding.
One way to cut the bottom of the notches is with a quarter-inch drill and a chisel, then finishingwith a rasp, or rough file, then a smoother file. The rasp and file are also useful for shaping the tips of the verticals, or just eliminating any splinters.
The hammer is needed for the nailing, of coarse. But the mallet is better for striking the chisel, because you need to watch the chisel blade, and because the mallet is so fat, you can't miss hitting the chisel. My dad and I made this mallet on a wood lathe many years ago.
Since making the cold frame, I thought that it could be used during the winter as a shelter for the birds that visit our feeders. So i removed the seedling trays, added a bed of leaves, small pots on their sides, and branches for roosting. The vent holes in the back were modified as entry holes.
The cold frame / roosting shelter was also placed on saw-horses to make the birds safe from predators.
I also made these seed-catchers from 1x4 lumber. Each half is 3x5 ft, -- overall size is 6x5 ft. The bottom is covered by porous plastic and hardware cloth, and the top with just hardware cloth, so seed falls in, but mice and rats can't get it. The closely-spaced boards at center front support me when I refill the feeders.
