The problems with using a plastic bottle as a clotch are that the bottle will fall over in any wind if the bottle is not pushed well in, and if it is pushed well in then the soil inside the pushed in bottle will dry out.
The following is an easy way to rectify both of these problems and an easy way to use a plastic bottle as a clotch. With a hot soldering iron, remove the bottom of the plastic bottle. While it is possible to cut off the bottom with a knife the action of the hot iron will create a ridge that stiffens the bottle end. Then again using the iron, create lots of holes in the base section that will be under the soil. The ridges created around the holes by the hot iron will actually stiffen the bottle, you can see the effect in the image.
The idea here is simple in that if you place this area of the bottle under the soil then the soil inside the clotch will not dry out as the moisture in the soil will feed through the holes and as the bottle is well down in the soil then this will also anchor it and work to prevent it from being moved by the wind.
