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If the soil is too dry, it will soak up all of the water from the jug before you leave on your trip. By the time you get back, there may not even be any water left in the jug. Water the soil before making the string drip system to avoid this issue. Position the jug so that it is out of direct sunlight; this will reduce the amount of evaporation. If you are only going for a few days and have a small plant, a mason jar will be enough. Don't fill the jug with water yet. This method will keep your plants watered for up to a week. The twine needs to be long enough to extend from the bottom of the jug to the base of the plant. If you can't find cotton or nylon twine, or if it is too thin, braid 3 strips of cotton fabric together, and use that instead. The string must be able to hold water. If it can't hold water, this method won't work. The string must reach the bottom of the jug. If you wish to water more than 1 plant, it might be a good idea to set up more jugs, 1 for each plant. This way, you won't run into the risk of the jug running out of water while you are away. If you have a few plants that don't require a lot of water, such as succulents, you might be able to get away with a single jug for 2 or 3 plants. Even if the jug does run out of water, your plants may still survive because of their water-retaining properties. The string needs to be about 3 inches (7.62 centimeters) deep. Also, make sure that the string is out of direct sunlight. Partial sun is fine, but if there is too much sunlight, the string will dry out before it can get the water to the plant. If your plants need fertilizer, you can also add some liquid fertilizer into the water at this time. If your plant is in a sunny spot, consider putting a piece of duct tape over the mouth of the jug; be careful not to cover the string, however. This will help slow down the rate of evaporation. If the jug is too low, put it on top of a book, a block, or an upturned pot to raise it up a little. This way, the water will be able to drip down the string.

Summary:
Saturate the soil before you begin. Place a gallon-sized (3.79-liter) jug next to your plant. Cut a long piece of cotton or nylon twine. Place 1 end of the string into the jug. Poke the other end of the string into the soil at the base of the plant. Fill the jug with water. Make sure that the mouth of the jug is above the base of the plant.