How I built a drying box:
Here's a rundown of my new drying box. First a little background. I usually harvest 2-4 plants at a time (6-10 oz per plant on average depending on strain). I cannot dry them outside my grow space, so I could choose between veg or bloom.
In veg, I tend to be lax about conditions. Temperature and humidity can vary and vegging plants are still happy. In my bloom space I am much more careful about conditions, carefully controlling temp, humidity and CO2 levels. Therefore I chose the more stable environment to site my dry box. It's slightly less convenient, but it will work (I've done this before).
In my bloom room I have an "AC tower", mentioned in the last post. Since I can't put plants under it anyway, it's a great spot for the dry box. In fact, this time around I built the tower with the dry box in mind. The tower holds the AC unit 6'4" off the floor so there is plenty of space underneath. The legs are 2x4. When I needed to brace the legs diagonally for stability I used (mostly) 3/4" plywood panels instead of diagonal braces. I built a box with a 42" x 28" floor space and 48" high. One side is open and framed with 2x4 at top and bottom. I didn't build to the floor because I want to be able to sweep and mop the space underneath without too much trouble.
I made a door out of 3/4" plywood and a piece of 1x4, and hung it on heavy duty hinges. For a latch I used a hasp and I put 1/2" stick-on foam gasket material on the inside side of the door to make it air-tight:
I needed a way to hang bud in the box for drying. Up till now I have used binder clips to attach stems to plastic hangers, but this eats up 9" of vertical space for the hanger itself, which would seriously limit how much I can dry in my box. I came up with a plan to allow me to work with 2" of overhead instead, allowing more than one tier in the box. I bought a nice piece of 1x4 hardwood 8' long. I marked a center line lengthwise and made ticks on the line every inch:
I then drilled a 5/8" hole at 71 of those tick marks. This took a while:
I used a table saw to cut the board in half along the line, bisecting the holes. I also cut the pieces into 18" lengths:
I then screwed these to the sides, with a gap at the front and about halfway back. I attached binder clips to 1/2 dowels the right length. Now I can clip the stems to the dowels and hang them in the box. This let me put an upper and lower tier. I allowed for 16" stems on the upper tier and 20" stems on the lower tier. I think I may reduce those lengths to get a third tier in there.
With this setup I can dry as much as 2 lbs at one go:
I used a 2-1/4" hole saw (meant to drill doorknob holes) to put a hole in the center at the bottom of the box:
I cut a 2'x3' piece of plywood and screwed pieces of 2x4 to one side at the corners. These will act as standoffs to hold the panel off the dry box floor:
I bought some flat black spray paint, a section of 4" duct, a 4" 'T', and a 4" elbow. I sprayed the inside of the duct pieces. This is easier before you snap the straight piece into a tube:
I also painted the center of the underside of the raised panel:
I painted the floor around the hole as well:
I shortened the straight piece of 3" duct, put the 'T' on the elbow and put the elbow on the straight. I cut a 3" hole in the back panel at the top and strapped the duct in place on the 'ceiling':
On the back of the box I sealed the duct to the panel with foil tape and attached a regular 120mm fan from a computer over the hole. The fan is turned to blow outward:
I used a computer power supply to power the fan. You can hot-wire and ATX power supply to stay on by jumpering the green wire the goes to the motherboard to one of the black wires on the same connector:
I centered the raised panel I made earlier in the bottom of the box. I then placed a 2'x3' mirror I bought at Home Depot for $30 on top of the panel:
Here is the result:
The fan stays on all the time. This draws an almost imperceptible flow of air in through the hole at the bottom. The air flows under the mirror and around the edges, further spreading the air. The air is drawn in through the two ends of the 'T' at the top and out the back. All the black spray paint prevents light from getting in. I tested this by climbing in (without the mirror in place of course) and having my wife close the door. It is absolutely dark in there. I then used a flashlight to see and hot-boxed the dry box. I watched the smoke to verify that it does not flow quickly anywhere. In fact it doesn't flow much at all. This is perfect.
I got a bucket of water and a rag and saturated all the wood surfaces inside the box, then closed the box and let it run. When it dried out I repeated this. I wet it down and dried it a total of three times. More would have been good, but I was out of time. Ideally I would repeat this until the wood suddenly takes a lot longer to dry on a cycle. Then I would open the door to help it finish drying and it would be in good shape. This saturates the wood and prevents it from absorbing moisture from the bud without the box actually being damp. This will let me avoid drying the bud too fast. I want it to take at least a week. Later I plan to line the box with spanish cedar or hemlock like a proper humidor.
Eventually I will use a humidistat to control the fan and hold a constant humidity in there, but for now this works fine. In fact, the first plant in was the first Super Lemon Haze I've grown. I have been monitoring the humidity and temps in the box and it is getting a range of 54-58% r.h. and 70-72 F, which is perfect. The temps will stay in the 70's and the humidity will drop when the room goes active, but it will be fine.
I'm planning to finish the dry box tomorrow, so I'll take pics and explain it in detail then.
