I agree with Earnest Sealey's review. The bottles must be taped in order to function consistently. Also, filling the bottles with sand (to a line you can't see) is messy and imprecise. A few stray grains of loose sand clog the holes and stop the water flow. Sadly, I ended up paying $$ to waste time. A better fix: going onto YouTube and looking at the videos about how to use soda bottles effectively to irrigate for free.
I have used earlier versions of these in gardens that are too far for my hose or I want to feed with liquid fertilizer. Worked well, but I left out over winter and the portion where the bottle connects have split. So, don't be lazy- take them in at the end of the season if you live up north.
I used these with 2 liter bottles and they worked great. I put them in my root pouches and loved the results. Obviously not all plastic bottles are made the same but I would say a majority would fit these. Good value.
This product is bogus. Please do not buy it. First of all the spike does not fit the bottle neck of any water bottle. Had to tape the bottle neck in order for it to fit. Having the spike screwed on properly and ensuring no leaks around the bottle neck plus following the instructions as written on the package, the water in the bottle (16 oz size) lasted only 10 minutes. I was expecting the water to drain out of the bottle for at least 30 minutes or greater. Gardener's Edge responds: For best results when using the watering spikes to gradually release water while you are away, thoroughly water the potted plant prior to putting a watering spike into the pot. If the planting mix is dry the watering spike will immediately release water and will continue to release it until the soil is fully dampened. That may use most of the water in the bottle very quickly, thus considerably reducing the watering duration. If the soil is pre-dampened, the watering spike will then release just enough water as the soil dries to keep the pot dampened.Many water bottles have been re-engineered to make less waste. Their screw tops are no longer as large and may not fit the spikes. Most soda bottles have the standard larger threading that will fit the water spikes well.