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Is it OK to repurpose plastic glasses as seedling containers for the mid-phase between initial development in trays, and final planting in the garden?

(I am going to make holes with a cigarette at the bottom of the each glass; this is the cheapest solution that I know)

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The glasses are available in sizes 200-500 ml.

EDIT: I read (see, for example, this question and this question) that light affects microlife in soil, and even that root can think it is a branch (!), so transparent or semi-transparent glasses would be in that sense unsuitable, but I hope, since this is only temporary, this won't have significant impact.

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  • I've done this a few times for that interim period, using the instructions that @Alina has provided. It has worked really well, and I feel good about re-purposing plastic. If for any reason the cups are too deep, or you come across deeper cups you'd like to use, just cut around the top. That way the roots will get the soil they need, and there won't be a problem with light. Also, as Alina said, smaller holes have been better for me, and a larger heat source, like a cigarette, can make a hole too big, and compromise the structure of the cup.
    – Sue Saddest Farewell TGO GL
    Commented Mar 20, 2018 at 21:23
  • @Sue OK, I gather a candle, a nail, and a pliers would work better than a cigarette. My first seedlings, of black-eyed Susan/rudbeckia, have slight tendency to develop tap root, and the more depth would be good for them, I guess. Thanks.
    – VividD
    Commented Mar 21, 2018 at 9:59

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Yes, it's ok to use them, and you can also make smaller holes with a hot metalic nail that you can hold with pliers. Just don't forget to trim the roots of the seedlings you are transplanting in plastic cups, especially if you have tomatoes. If the seedlings have a tap root, try to place them vertically.

And try to fill the cups with soil as much as you can, because rims may cast a shadow and lead to etiolation. If the soil becomes more compact after a week, push upwards the bottom of the cup in its center in order to raise the soil level, even if the plastic bottom becomes wrinkled.

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  • Thanks for so many useful hints! I updated the question with some concerns about light affecting the soil, hope this is not a significant problem.
    – VividD
    Commented Mar 20, 2018 at 20:31
  • @VividD I'm not good at aspects of microlife and soil, so I can't say anything about it, but I have used transparent ones to keep grapefruit and passionfruit seedlings for a few months and they grew well. And I have kept Hoya carnosa plantlets (from leaf cuttings) in transparent plastic cups for almost a year, again with no problem. What I like about the transparent ones is that I can grow plants without making holes at the bottom because I can see how wet or dry is the soil and I know when to water. This was because I didn't use saucers (lack of space, lots of plants).
    – Alina
    Commented Mar 20, 2018 at 22:42
  • Right, transparence has its pros, and perhaps some cons, but those cons are not so serious, I guess. You success with grapefruit is encouraging. Thanks again.
    – VividD
    Commented Mar 20, 2018 at 22:45

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