Introduction: Rooting Greenhouse Pots From Two Liter Soda Bottles
Several years ago, my wife and I made the move from suburbia to some acreage a few miles from town. Over the years, I've developed an interest in growing fruit trees and berries for our own use. So far I have been purchasing the plants I wanted, but that can get a little pricey if you have the room and inclination to plant more. Now after some research into propagating the plants I have, I began making single plant greenhouses from soda bottles for rooting the cuttings I take from our existing plants. Self-watering pots are frequently covered in other peoples instructables, so I'll leave that to the reader to investigate. I will show my method of making them, however, as it speeds the process quite a bit. I'll also share the mixture I use in the pots to encourage root growth. Now on to the process.
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Step 1: My Bottle Cutting Jig
Since I planned on making a substantial number of these, I started by making a jig from some scrap boards I had around the shop. The cutting tool I use is your average Dremel Rotary Tool, which I clamp to the front strip on my jig to position the fiber-reinforced cutting wheel where I want the bottle cut. I experimented with the dimensions of my jig so that the wheel just cuts through the plastic. As I have two different cutting positions for my pots, I marked the wheel position for quick set-up of the cutter.
Step 2: Cutting the Bottles
I make my rooting pots from two bottles, one for the pot and another for the cloche or greenhouse top. It's not particularly important, but I prefer the green bottles for the pots and clear for the tops. I haven't been able to determine if it really matters. I plan my cuts at the place on the bottles where the straight walls meet the curved top/bottom. The Dremel tool cuts best using the fiber-reinforced cutting wheels and I have cutting several hundred bottles without breaking one, while I broke the non-reinforced ones regularly.
The edges of the bottles are a bit rough, but nothing to be concerned over. After cutting the green bottle, I remove the cap and then insert the top upside down into the bottle to form a funnel at the bottom. I doubt this is necessary, but I find that with it I can see any water that pools in the bottom if the pot is over-watered. If using these to actually grow plants without the greenhouse, some drain holes an inch or so above the bottom can be added to the bottle walls to allow proper drainage. I just use the Dremel and cut small slits spaced around the bottle.
Step 3: Heat Forming the Top to Fit Into the Pot
My next step is also my preferred method for having the bottles fit together snugly to retain moisture while the cuttings form their new root systems. To do this quickly and reasonably accurately, I use an old wine bottle which the top bottle fits over loosely. The wine bottle is only just smaller around than the soda bottle, giving me the desired step-down when the plastic is heated. Since I don't want too much of the plastic to shrink, I cover the plastic bottle with a piece of drain pipe that I split down the side. This shields the plastic from the heat while I'm shrinking the bottom inch or so. Using the heat gun on low, I rotate the plastic bottle on the glass bottle until I have shrunk the bottom inch all the way around. It's a good idea to remove the cap of the plastic bottle either before this step or at least before trying to remove the plastic bottle from the glass bottle. The seal is pretty impressive on the glass bottle! In the last photo, you can see that the bottom edge has been reduced just a bit. Some type of glass bottle or similar cylindrical object is necessary to limit the size the plastic shrinks to, as trying to freehand this with the heat gun produces a wavy, crazy looking edge. The first picture shows the two bottles nested together.
Step 4: Starting Your Cuttings
Sorry to the folks that tried reading this step before. Guessed it fritzed out during the upload and I didn't catch it. Anyhow, I'll get to the bit about starting your cuttings. The mixture I found online that works for us is equal parts of sand, composted sphagnum peat moss, and vermiculite or perlite. I used vermiculite with the first batch, but have found the large bags of perlite at my Home Depot to be a little cheaper, so that's what I'll be using next batch.
After mixing and filling your bottles, moisten it well, but don't drench it. There are quite a few pages out there on how to take and handle your cuttings, and after finding what you need for your plant type, place them in the bottles and tamp it down a bit. I use a powdered rooting hormone on the cut end before inserting it into the rooting mixture.
The photos above show our first try at blueberry cuttings. We started with approximately 6" cuttings from the tips our donor plant, picked all but the two top leaves off, and nicked the outer layer at the cut end before dipping in the rooting hormone. The plants can be misted through the top just by unscrewing the cap or you can easily lift the top bottle off. The last photo shows the new growth beginning after about 4-5 weeks...ready for repotting into a new pot of prepared acidic soil to grow a bit more before we plant them in our raised beds.
Rooting times vary according to plant type. We have had some ornamentals root in two weeks, others are taking much longer. So far we had a failure rate of about 20%, but new cuttings are fairly easy to start and we are learning as we go on what our plants need. Good luck to you and happy gardening!