Gardening in cold climates may require that you get a jump-start on the season. Cold weather and long winters may also leave gardening fanatics with an itch to plant something. Both of these issues can be resolved (at least partially) by building a grow light. While many grow lights are designed and built for indoor use where the climate is controlled, I was able to build a grow light that works well in my garage even during the winter.
Grow Light Size
The size of your grow light will depend mainly on three preferences that will vary from person-to-person:
- How much do you want to grow?
- How much space to you have?
- How much do you want to spend?
The first two of these can be mitigated using the grow light design that I used (modular). Spending can also be mitigated depending on how patient you are and what types of scraps you happen to have laying around.
I designed my grow light to be approximately 2′ x 4′ x 3′, or two feet wide, four feet long, and three feet tall (with only about half of the height available for the plants). However, the design is also modular, so after my first module was successful, I added a second level which was 2′ x 4′ x 3′, with most of the height available for the plants. I’ve found that this size is pretty reasonable. It allows about 8 square feet for plants and the height is enough to grow basil, lettuce, onions, tomatoes, and many other crops so that they’re tall enough to transplant into the garden.
Grow Light Design and Materials
The grow light design is fairly straightforward.
List of Materials (these can be altered depending on your preferences, but this is basically what I used for my grow light):
- Four 2×4’s at 36″ long — these form the four vertical corners
- Two 2×4’s at 45″ long — these run lengthwise about a foot off of the ground
- Two 2×4’s at 24″ long — these run width wise
- Two 2×4’s at 27″ long — these go across the top, width wise
- Three 2×4’s at 48″ long — these go across the top, length wise
- A piece of chicken wire approximate 2′ by 4′ — attached to the level where the plants will sit on
- Metal strips used with chain-linked fences
- Two 12″ x 48″ T8 fluorescent light fixtures OR Three 7″ x 48″ T8 light fixtures (the more light the better)
- Either four or six 48″ T8 fluorescent light bulbs (depending on how many fixtures you want to use
- A 5-6 light incandescent fixture, the type that are used for lighting bathrooms
- A couple 60W Halogen flood lights and or a few 60W incandescent lights (before they are outlawed…)
- A timer to shut the heat on and off
- A piece of clear plastic about 10′ x 8′ to cover the whole thing
The 2×4’s will basically form the structure of the grow light. This has been described a bit above. Basically just use the 36″ pieces like legs of a table. Then you will have 2×4’s connecting these legs on the top side, and another set of 2×4’s connected them about a foot off the ground.
On the 2×4’s that sit on top of the contraption, connect the fluorescent light fixtures. Use adjustable chains so that you can keep the light close when the plants are sprouting, and then move the light higher as the plants grow. You want the lights to be about one inch above the plants, but be careful because the plants will quickly burn and dry out if they touch the lights.
The chicken wire is used to form a level platform to place the plants on. It is stretched and nailed to the 2×4’s that are about a foot off the ground. However, since the chicken wire flexes, you first need to place some stronger strips of metal across the 2×4’s every foot or so, then put the chicken wire on top. This way, when you have a tray full of heavy, water-logged dirt, it won’t cave down the chicken wire. You can kind of see the chicken wire in the photo below — it’s doubled over (two layers). If you look at the photo at the very top of the post, you can see one of the strips of metal just under the tray of yogurt containers.
Under the chicken wire (on the ground), you will place the 5+ light fixture and put a couple of halogen or incandescent light bulbs in it (just regular bulbs, you don’t need reptile bulbs or anything). These provide heat for the plants resting on the chicken wire. This method is way cheaper and easier than warming-mats. It also uses less power (I think). However, I’m not sure about the fire hazard. I place it on my cold cement floor in my garage, so I’m not too worried about the fire hazard. When I was thinking about how to warm my plants, a guy at Home Depot didn’t think this method would work. But it does! Especially if you place your plants on metal trays or cookie sheets. They warm up quite nicely. In fact, I recommend placing a simple $10 timer on the plug that connects to the light fixture so that the plants don’t burn — just cycle the fixture on and off every hour or so. You’ll get a good idea of how warm it is when you check the plants every day or two. Look at the photo on top of this post and you can see the light fixture under the plants.
The photo below shows the plastic covering. The cover keeps the heat inside — most of the heat provided for the grow light comes from the halogen/incandescent light bulbs below, but some also comes from the fluorescent bulbs.
Just fold it back to access the plants.
I’ll let the pictures provide some other detail. Basically, the dimensions aren’t super important, it’s a very easy design.
One nice thing about this design, is that you can easily expand it vertically by building something similar right on top of it, as I have done. I also added some wheels so that I could move it without having to drag it around.
I water the plants in my grow light every two days or so. Basically just moisten the dirt whenever it starts to get dry. As you can see from the photos, I’ve tried many different containers. My favorite containers for single plants are yogurt containers. They keep the moisture in really well, the plants and dirt slip right out of them, and they are free if you eat yogurt anyways. Just cut a few holes on the bottom edge to let them drain a bit (make it look like one of the black pots you get at the nursery). I don’t like the peat pots — although you can see that I’ve tried them. They dry out too quickly and are harder to plant unless you’re willing to plant the whole thing (I just don’t trust that the roots can get through them…). For onions you can just plant in a big, ~2-3″ deep baking sheet. If you want to plant basil, plant about 6 seeds in a ~4″ deep aluminum sheet. You can harvest the leaves under the grow light a few times. When the frost has past, you can just plant the whole tray of dirt into your garden (try to keep it all in one chunk when you take the tray off). Then they’ll grow into a big bush.
Lettuce (great to give it an early start), cilantro, and onions:
Flowers in back-left, basil in back-right, carrots in front-right (these didn’t really do great — maybe I could have transplanted them, but I’m not sure), and some tomatoes that haven’t sprouted yet.
I switch off the fluorescent bulbs in my grow light every night when I go to bed and let the warmer lights cycle about every hour depending on the temperature in the garage. Contrary to what some may say, I don’t think plants actually need a “night-time” to grow properly. You can probably just leave the lights on all day and night. Photosynthesis has a “Light Reaction” and what is sometimes called a “Dark Reaction.” However, the “Dark Reaction” is more properly a “Light-independent Reaction” — it can happen in the light or the dark. Nevertheless, I figure the plants don’t need more that 16 hours per day and I don’t want to kill my electricity bill.
Cost of Running the Grow Light
To calculate the cost of running your grow light, just add up the watts of all your bulbs. For example, I think I use six 30W fluorescent bulbs, and two 60W halogens. So the total is 6*30 + 2*60 = 360. Divide this by 1000 to get the kilowatts/hr –> so 360/1000 = 0.36. Now look on your utility bill to see how much you pay for electricity. I pay about $0.09/kilowatt hour (electricity is cheap in Idaho). Therefore, my hourly cost is $0.09 * 0.36 = $0.0324. Assuming I run it 16 hours a day, that’s 16*0.0324 = $0.51/day, which is $15.55/month. Not too bad. You can grow enough tomatoes, peppers, and onions to justify the expense of running it. Also, if you extend it vertically, it gets a little cheaper per square foot.