Beyond Straw Bale Gardens: The Six-Week Greenhouse

How to Condition Straw Bales to Generating Heat

Beyond Straw Bale Gardens: The Six-Week Greenhouse

Reading Time: 7 minutes

A new gardening trend gathered steam in 2013: grow vegetables out of an agricultural waste product, with a method that eases the back while building soil for future gardens. Straw bale gardening drew a lot of skepticism. But it works.

I tried my first straw bale garden in 2015 after meeting Joel Karsten. I purchased his book, found some clean rice straw, and got to work. At the same time, a disabled friend gave it a try and discovered a way to cultivate food without relying on help from others after the initial garden setup.

Since then, I’ve moved away from that tiny city plot and onto an acre of land. I have about 1/5 of an acre, just dedicated to gardening. I also planted 40 bales this year. Why? Because I had the old hay that had gotten wet, so I couldn’t feed it to my goats. I had the space. And all these years of straw bale gardening proved how much soil it creates. Even if the gardening year is sub-par, decomposition within the bales will boost my in-ground beds next year.

The straw bale gardening method can be used on existing soil, whether good or bad. It works on top of driveways, gravel, hard clay, or pallets. The bales can even sit on raised surfaces to bring the gardening surface even higher.

The Six-Week Greenhouse

Gardening where I live in Northern Nevada presents challenges, one of which is the short growing season. We’re lucky if we get 120 frost-free days in a row, so frost-sensitive plants MUST be started ahead of time. I tend to plant 50 or so tomatoes, 30 pepper plants, 30 eggplants, and a lot of basil, so I’m not willing to spend $600 for plants. But seed-starting is another challenge. Those seeds all want specific temperatures for germination. Plus, once they sprout, they need good light FAST, or they get weak and leggy. Plant lights usually aren’t enough; they crave the sunlight.

In Straw Bale Gardens Complete, Updated Edition, Joel describes a cost-effective way to use the gentle heat created from decomposition as a way of warming those seed-starting trays. The clear plastic of a budget greenhouse frame provides sunlight right when the plants sprout.

It’s a win. And it’s something I had been doing for several years. Why didn’t people know about this?

Joel calls it the Six-Week Greenhouse. Count back six weeks from your area’s average last frost date. That’s when you build a frame using two cattle panels, lumber, clear 4-mil plastic, and a few bales of straw. Condition the straw to begin decomposition — set seed-starting trays on the bales, filled with the sterile medium and the seeds. Lift the trays whenever you need to fertilize or water the bales, then place them back down. Decomposition provides that comfortable 70-80 degrees F for tomatoes, peppers, and eggplant.


In the old days, Joel explains, pioneers had no greenhouses, so they went on the south-facing hillsides, dug them out, filled the bases with fresh horse manure, and put window frames on the top to make cold frames so they could start seedlings. As manure decomposes, it gives off a lot of heat. The decomposing bales give off similar heat. Adding cement blocks, rocks, or concrete inside the greenhouse helps absorb heat during the day and radiate it at night.

At the end of that six weeks, if the weather looks good, peel the plastic from the greenhouse if you wish — plant tomatoes or vining crops in those bales and allow them to climb the cattle panels.

No, it’s not a beautiful glass greenhouse. But it costs less than $100 to build, and if you reuse the frame next year, you only have to purchase more bales and more plastic.



• Two cattle panels: 50” x16’
• Two 2” x4” boards: 104” long
• Two 2” x4” boards: 84” long
• Two 10’x25’ rolls of 4 mil clear plastic
• Two 16’ lengths of polyethylene pipe or old garden hose
• Sticky-back 6’ zipper, such as Zipwall brand
• 3” wood screws
• Zip ties
• Staples and staple gun
• Roll of clear packing tape or greenhouse repair tape


1. Arrange the boards into a rectangle, with the boards resting on the 2” sides. Nail or screw them together, so the 84” boards rest inside the 104” boards.

2. Stand your first cattle panel inside the wooden perimeter, so it forms an arch, with both ends of the panel touching the ground. Be sure the smooth side (long wires) is to the outside, and the crossbars of the panel are to the inside. The panel ends should rest against the 104” side, forming a 6’ arch.

3. Position the second cattle panel beside the first to create a 9’ tunnel. Zip-tie the two panels together, with the sharp zip-tie ends pointing to the inside.

4. Use the fencing staples to attach the bottom edges of the cattle panels to the wooden frame.

5. Use zip-ties to attach one length of hose or plastic pipe to the edge of your front cattle panel. Repeat with the back edge and the second hose.

6. Set the frame in its permanent location. If wind is an issue, stake the frame to the ground. Or fix boards along the bottom, connecting the two ends, and set the straw bales on top of these boards to hold the greenhouse down in the wind.

7. Carry your straw bales into the frame and arrange them along the edges with room to walk through. You can fit six two-string bales inside or four to five three-string bales.

8. Covering the arch: Unroll one roll of plastic, so it lays across the arch. Attach the end of the plastic to the wooden perimeter, then pull the plastic taut over the frame, trim it to fit, and attach the other end. Now carefully unfold the plastic sheeting to neatly cover both cattle panels and staple it securely to the wooden frame, pulling the plastic snug and stapling every few inches. Now staple the front and back ends of the plastic to the hose.


9. To create the front and back walls: Using a few staples, attach the second roll of plastic to the top of the arch, at either the front or the back. Unroll it and trim at ground level. Unfold the plastic to either side and staple along the perimeter, into the hose and the wooden frame. Repeat on the other side to create both a front and a back wall. You can use the folds in the plastic as guides to be sure you have it on straight.

10. Seal the seams, where sheets of plastic meet, with the packing tape or greenhouse repair tape. This is important since the staples won’t hold forever.

11. To build the door: A Zipwall is a huge, sticky-back zipper. Peel off the first few inches of backing at the bottom part of the zipper, then stick it to the top-middle part of the front wall. Work your way down, peeling off backing and adhering the zipper to the plastic, all the way down. Then open the zipper and slit the plastic through the gap, creating the door.


Was this confusing? You can see a video at:

StrawBaleGardenClub. com/6WeekGreenhouse

Conditioning the Bales

12. Sprinkle 1/2 cup of a high-nitrogen fertilizer onto each bale. Lawn fertilizers are great but do not use fertilizers with weed and feed. Water that fertilizer into the bales very well.

13. Just water down the bales.

14. Repeat step 1.

15. Repeat step 2.

16. Keep doing this for about 10-12 days.

17. Sprinkle on 1/2 cup of 10-10-10 fertilizer — water in.

If you insert a compost thermometer into the bales, you will see the temperature rising after six or so days. Within the greenhouse, it takes even less time. Microbes, stimulated by the fertilizer, start to consume the straw and turn it into soil. This creates heat which warms the greenhouse. Once you feel a little heat coming off the bales, you can set your seedling trays on top of them and let the natural heat warm the planting medium.

For more complete instructions and explanation, visit our story at Countryside: growing/straw-bale-gardening- instructions-how-it-works/ or visit Joel’s website Straw Bale Garden Club

Need a Boost?

These instructions can be confusing, especially when it comes to gardening in straw bales when you’re used to gardening in dirt. After a while, you will master the learning curve, and it gets simple. But until then, there is plenty of help available.

Since publishing his book and spreading the word about straw bale gardens, Joel has received many questions. One of the most prominent regards the type of fertilizer to use. What, exactly, does he mean by a “high-nitrogen” fertilizer, and just how bad for plants is fertilizer with weed and feed? (It’s deadly.) And how can you do this organically? To address that, Joel’s team created BaleBuster in both refined and organic formulas to take away the guesswork.

BaleBuster sells in bags portioned for specific garden sizes: BaleBuster20 provides enough refined (conventional) fertilizer for 20 straw bales, while BaleBuster5 provides enough organic fertilizer for five bales. Both fertilizers also contain bacterial strains Bacillus subtillis and Bacillus megaterium, to aid decomposition, and spores for Trichoderma ressie, a fungus that helps plant roots absorb nutrients. The bacteria and fungi give bales a boost that you won’t get if starting with clean, dry straw. The organic fertilizer uses blood meal for nitrogen, while the refined fertilizer utilizes conventional NPK. Both eliminate the need for the 10-10-10 fertilizer at the end of the conditioning process.

For additional questions, you can join the Straw Bale Garden Club. A free membership gives you access to videos, a community forum, and your questions answered by Joel himself. Paid membership levels also give you access to webinars and discounts for purchases such as BaleBuster. The top membership tier unlocks a half-hour live presentation by Joel, specifically for your group or class via Zoom.


Though the straw bale gardening trend seems to be on a decline, those who have tried it are still believers. I am. And I advocate any method that turns those old, “waste” bales into good soil for the future.

Have you experimented with straw bale gardens? Were you successful? We would love to hear from you in the comments below!

Originally published in the January/February 2022 issue of Countryside and Small Stock Journal and regularly vetted for accuracy. 

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