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I'm having tomatoes in a little greenhouse. I water them by using plastic bottles where I cut of the bottom part, put them a few cm into the soil and fill them each two days entirely with water (+- 1 l). I fill the either in the morning or in the evening.

Now I had a discussion with my mom about the details of watering with bottles.

  1. She recommended me to fill the bottles with soil, for water to infiltrate more slowly. I was thinking that when the bottle heats up during the day, much water would evaporate and would not be used by the plant. At the same time, if water infiltates deeper, roots of the tomato plant will have to grow deeper, creating a stronger plant. But she told me that water would drain very fast too deep and would get lost that way. It is important to know that we have a very sandy soil and from a depth of 20 cm and deeper, organic matter content is very low.. (as I added compost only in the upper soil).
  2. She also recommended me to direct the bottles towards the plant... for more or less the same reason, so water can be more used for the plant and drains less. While I thought it is better for the plant to have to need to grow deeper.
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My assumption is that your question is something like "what' the best way to water these tomato plants using a water bottle system?"

So what you want, I believe, is a slow release of the water into the soil. Your mom is right that a slower flow is best. If the flow of water is too fast it'll just wash right through the soil. That doesn't do the plant any good and just wastes water.

An alternative idea that I've used in the past is to punch some holes in the bottom of a plastic milk jug or a plastic 2 liter soda bottle. I leave the lid on the top of these and that helps slow down the flow and minimize how much evaporates. I used this method through the garden one year and it worked pretty well. I punched holes only on one half of the bottom of the bottles and put that side closest to the plants. Worked pretty well.

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Tomatoes have two sets of roots. The roots near the surface take in nutrients, and the deeper roots bring in more water.

So the purpose of burying bottles, or pipes, is usually not to slow-release water, but simply to deliver water to the deeper soil where the lower roots are.

A common approach is to cut the bottom off a 2 litre drink bottle, then bury that neck-down (lid off!) its full depth, so it acts as a funnel carrying water to the bottom. I've seen other people use perforated drainage tubing, cutting it to 16" lengths and burying vertically.

Don't worry too much about water draining away. Deep roots are a good thing. Even sand will hold in a fair amount of water, and the plants will slurp up water before it drains away.

Don't add feed to the water you deliver this way. Water with feed at the surface, or add a compost mulch, because it's those shallower roots that take in nutrients.

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