Sunday, October 13, 2013

Seedling and Cutting Grow Box

After increasingly using thyme, marjoram, oregano and rosemary in my cooking recently, I resolved to purchase a plant of each, knowing they were on sale at a local grocery store. While I purchased a thyme plant--Thymus vulgaris, specifically--I forwent purchasing individual marjoram and oregano plants in favor of a hybrid of the two--Origanum x majoricum. Regarding the rosemary, I've noticed multiple rosemary plants near my home, and decided to take cuttings of the rosemary in lieu of purchasing a plant that I understand to be easily grown by clonal propagation. While in the past I've simply put cuttings I've taken in a bag under a light, I decided to convert an amazon shipping box to help these cuttings take root.

The box is a size 1BA (19" x 12.25" x 11.25"), that I received from Amazon for a moderately large delivery. I took said box and cut in half the front flaps, taping the top halves together and leaving the bottoms free to serve as doors. On the bottom of the top flaps, I used a strip of folded aluminum tape to serve as a sealing/light blocking strip which I duplicated for the right door, the latter of which is barely visible in the following picture of the unit with its doors opened.

When the unit is sealed, very little light escapes through the doors as a result of the previous sealing strips and the inner flap of the box, which was retained in the final design, and which is held closed over the bottom of the doors by way of strips of duct tape that are fastened to the sides of the box. As you will see, there is also an upper, tapered flap that I attached for the purpose of duplicating the benefit of the bottom flap with regard to its light blocking potential, as well as its role in helping the doors stay shut, as pictured below.

Also included is a food-grade thermometer, pictured above, that is pressed through the tape above the door to provide a measurement of the temperature inside the unit. I've also glued a piece of white drawing paper to the front of the box for the purpose of recording when plants have been put in (which you'll notice I have forgotten to use for this first batch). When in use, the light that I've selected provides a sufficiently intense, even illumination for the plants.

The light I have selected is a Philips LED flood bulb with a "Daylight" color profile (5000K white). This provides a very blue-tinted white light (as was typical with early "white" LEDs), that I understand is well-suited to vegetative growth. 

As an aside, the emission spectrum of these white LEDs (which are the same as "Royal Blue" LEDs, but with additional phosphors to even the light out to blueish-white by adding green-yellow-orange light) corresponds roughly to the lower absorption maximum for chlorophyll b (with peaks at 453nm and 642nm) while almost completely missing that of chlorophyll a (with peaks at 430nm and 662nm). Conversely, the red LEDs popular in flowering bulbs are usually red at 660nm, corresponding to the upper absorption maximum for chlorophyll a. To extend this briefly into speculation, a page on planted aquarium lighting indicates that red light stimulates "long, leggy growth" while blue light stimulates "compact, bushy growth", which, given the use of red LEDs for flowering and blue LEDs for sprouting, leads me to believe that chlorophyll a is mostly responsible for plants growing towards light and flowering, while chlorophyll b is more responsible for root formation and growth thickening.

That said, the bulb that I selected, while using LEDs, produces enough heat that I felt I should vent the box somewhat to allow the heat to escape. To do so, I cut holes in the left and top of the box, and covered the holes with lengthwise-cut halves of toilet paper tubes, taped down with aluminum tape.

This mitigates the problem well enough, with observed temperatures inside the unit (after having it on and closed for some time) being only 2-3 °F over ambient, thought the heatsink portion of the bulb is decidedly quite hot. As I expected that even an LED bulb would still run quite hot in an enclosed space, I used a mountable ceramic lamp socket purchased from a chain hardware store, mounted through the top of the box with a disc of cardboard used as electrical insulation. The hole near the pictured socket is the top vent.

While I have yet to confirm that the cuttings will be viable (as I only took them 3 days ago), I feel positively about the execution and design of the unit. Having been made with a cardboard box, the total cost of parts is around $25, with the LED bulb responsible for about $20 of that figure. I also feel positively about posting again, having taken a significant break after moving from College Station to another Texas city. As I've been engaged in more creative ventures, like this one, I hope to provide more regular updates. 

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