Set Your Garden on Fire

April 23rd, 2013

I’m being quite literal, the title of this blog post is “set your garden on fire” and I literally mean that. Burn it down. Why? Well, let me explain….

In the vegetable garden weeds are horrible, no one likes weeds, they compete with our crops. Also, unless you’re practicing no-till, you’re going to turn the soil every Spring to loosen it up and aerate it, giving plant roots an easier time of things. Unfortunately this soil turning brings new weed seeds to the surface, and you might particularly be susceptible because you bought a bag of questionable compost at some point that was just full of weed seeds. What you need to do is stop those weed seeds from sprouting. You could use a natural or synthetic pre-emergency herbicide, but that will also stop your vegetable seeds from growing. You can deal with the seeds after they emerge, but that can be a losing battle, so what is a good gardener to do?

Option 1 is solarization, this refers to cooking your soil with sunlight. You simply put a layer of clear plastic or glass over your garden (raised beds work best) and let the sunlight soak in. Ideally the air space in between the plastic/glass and the dirt will rise to a high temperature, high enough to kill weed seeds on the surface (while also warming the soil). This works, if you have the plastic/glass, want to mess with securing it, and get adequate sunlight early in the growing season.

Option 2 is setting your garden on fire. Different method, same result, you cook the top inch or so of soil, killing any dormant weed seeds that you just turned up. If you use raised beds and are worried about the wooden sides, don’t be, the soil will keep them cool enough. Fire has the additional added benefit of potentially adding nutrients to the soil, as well as bio-char. Bio-char is a fancy word for essentially natural charcoal or carbon, as we all know from the use of activated charcoal filters charcoal bonds to other chemicals, like say nitrogen and phosphorous, holding such minerals in the soil. It is theorized the use of charcoal to create the soil called terra preta is what allowed the indigenous people of the Amazon to grow food in what is otherwise a wet desert, thousands of years later the soil is still fertile.

I’ve touched on this topic before in my fertilizer from the ocean post where I mention taking the used activated charcoal from aquarium filters (now blissfully bonded to nitrogen) as a soil amendment. There are lots of bio-char advocates out there who would have you build hardwood fires in your garden every year and till the resulting charcoal into the soil, and indeed you can do that, though it is more work than I have in mind.

Of course, there are some minor PH issues with ashes, but it is a small amount and I’m not wholly concerned with it, and it can be corrected easily if you discover a problem.

So, what I did this weekend is first amend my soil. Last fall I emptied out my compost tumblers (link is the model I have), and put that in the garden, so I didn’t add more compost this Spring, instead I added fish bone meal (also mentioned in my fertilizer from the sea post) and azomite, which is a mineral amendment. I would have also added some nitrogen fertilizer in the form of blood meal or fish emulsion, but I didn’t have any. I then work it into the soil and turned the soil over to looser it up, and raked it smooth. Next step was to put down a layer of corrugated cardboard, on top of this I tossed a bunch of wrinkled newspaper, some various dry sticks, twigs, and leaves lying around, and on top of it all I poured about a gallon of used vegetable oil from my deep fryer (the oil helps it to burn longer/better).

You can’t really light this well with a match, the cardboard is in direct contact with soil and needs more than that it get it really going. I used a propane torch which I got for Christmas, and it is an excellent gardening tool. Imagine, weeding with fire instead of chemicals? I wanted it specifically for this garden prep application but it is a multitasker. This sucker gets hot and sounds like a jet engine. In addition to lighting the top of the pile, I was able to direct the flame underneath the layer of cardboard, superheating the air between the cardboard and the soil and creating combustion, that really got it going, and probably 95% of the flammable materials burned up. So I consider it quite successful.

Now, this did not produce a lot of charcoal, so the bio-char value is limited, but I wasn’t going to re-till the soil (thus bringing up more weed seeds) to work any big pieces of charcoal in, otherwise I would have added more large wood pieces. I do put charcoal I produce in my fireplaces etc into my composters. If you want to experiment more with charcoal and bio-char, the best way is to collect a bucket of it, then pee into the bucket. This way, you’re pre-seasoning the charcoal with nitrogen, rather than have it pull it from the garden once you add it to the garden.

I’ll update this post if I notice a reduction of weeds this season, but I think it was successful, it got really really hot.

When I was done and it was cool I planted carrots, lettuce, kale, beets, and spinach. Gardening has begun (hopefully).

I used this to prep my vegetable garden, but it also works to clean out an ornamental garden if you take over one that has been neglected, gone to weeds, and you just want a blank slate.

PS. It goes without saying, fire is dangerous, be careful, keep a hose handy, possibly wet down the areas around your garden, don’t do this in dry conditions, and check to see if you need any sort of permit.

Posted in: Edible Gardening, Gardening, Troubleshooting »

8 Responses to “Set Your Garden on Fire”

RHGentry Says:
April 29th, 2013 at 12:05 pm
I’ve done something similar in the past. I raked my fall leaves into the raised garden and burned them. The only problem was it did burn the wooden boarder and the smoke kept shifting in direction that were not pleasant. I like the plastic cover idea better.
joyce Says:
April 30th, 2013 at 8:28 pm
this really makes me want to go right out and start
layering paper and cardboard,etc. I would love to start a fire but here in N. CA its a little dangerous after May 1st. thanks much for these articles. joyce
Spencer Nitchie Says:
May 15th, 2013 at 2:28 pm
Instead of cardboard and paper (which might have weird ink and glue) maybe use instead, old christmas trees and clippings from rosemary bushes, or other oily evergreen branches.
Administrator Says:
May 18th, 2013 at 5:07 pm
That stuff would be good too Spencer, old christmas trees sure do burn nice. But never fear the inks and glue, they’re plant based biodegradable on those products (for instance, black and white newspaper uses soy inks).
Linda Says:
May 26th, 2013 at 11:07 am
I had the same concern as Spencer as I was reading your article. Thanks for clearing that up. Lots of great info. Thanks again.
Kris M. Says:
June 27th, 2013 at 8:37 pm
Cool! I don’t think my wife would let me do this, just because I can be a bit of a pyromaniac 😀 but it’s good to know this, Thanks for sharing!
Gary Says:
July 19th, 2013 at 5:57 am
I have struggled with the solar method to burn the weed seeds and when I read your blog I thought that was a very good idea. I hope it works well with devil grass as that is my biggest problem. Thanks for the idea.
Yourgardenstop Says:
September 4th, 2013 at 6:43 pm
This is a great idea. I changed over to a raised garden bed. I also gather the leaves and cover the soil in fall. I have a yard vac/mulch that i suck the leaves up first with. This breaks them down making it easier to try. This way the leaves will dry faster.