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I was using old clear (transparent) plastic meat packaging to grow plants in. Is that a good idea? Are there any side effects of roots possibly being exposed to the sun?

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6 Answers 6

up vote 14 down vote accepted

Roots exposed to the sun might think they have reached the surface and start to put shoots out.

Those particular containers don't look very strong - don't underestimate the weight of wet soil. Ideally you should have some more rigid that does not collapse under the soil's weight or when you move them.

Do these containers have holes in them? Holes in the bottom are required for drainage, but holes in the side could wet (and degrade) black paper/card as recommend by @shanna.

Plastic pots can be okay, but you need something stronger and opaque. All plastic pots will eventually degrade with the UV from the sun. Perhaps not a significant problem at high latitudes, but here in Texas, they definitely have a limited life (as does plastic garden furniture!) and some are better than others.

@gunbuster mentions plasticizers. I suspect in this application they are less of a problem than in food containers, but this is another good argument for containers that are sold as plant containers.

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If you're stuck for containers and this is your only option (or you want to be environmentally friendly and re-use those pesky non-recyclable food trays), you could glue something like black paper or cardboard to the outside to keep the light from getting through.

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Plastic is not a good medium. It traps heat, melts in high temperatures and contains plasticizers (especially in soft plastic like yours) which may dissolve into the soil.

In addition, your container is too shallow for most plants. It can only be used as container for plant germination.

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What do you mean when you say that you are using clear plastic containers to grow plants?

Starting from seed, as seedlings, indoor plants that don't want direct light and whose roots aren't totally root bound?

I suspect all of the above would be fine, although the indoor plants may have problem with not enough soil depending upon the plant. Similarly, there may be some seedlings which need deeper soil level than that.

The other replies are all applicable, but I can think of situations where it would not be a problem, and there are probably others. What is your goal, and what are the specifics?

curious

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Clear pots can be great for plants, especially transplants. Plants vary a lot, but in general, the roots reach the edge of a clear container, feel the sun, and stop growing. This prevents them from getting root bound. Once transplanted into the ground the root start growing with a minimum of transplant shock. Broccoli is an example of a traditionally transplanted crop that can really root bind and benefits from clear containers. Better yet is soil blocks...no pot. Blocks work great for large operations. Gardeners may find clear cups more convenient and economical.

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I have been using plastic shoe boxes with transparent fitted covers or with plastic wrap covers, plus salad green boxes and other such transparent boxes for 5 years now with:

  • never a box lost to disintegration into the soil
  • never a problem with plant's roots
  • with care about ventilation and placement such that plants would not overheat
  • care to inspect the contents frequently enough to verify that there would be enough moisture in the box
  • place drain holes through the bottoms of some boxes that contained plants that needed watering as opposed to misting with rainwater or distilled water
  • care that tap water salts from the dissolved solids in most of our tap waters did not concentrate in the potting medium as moisture evaporated from the boxes
  • care that boxes that were not adequately vented for pressure changes with changes in ambient temperature did not suck in misting water that was too high in dissolved solids, etc.
    I would further say that I had to learn some of what I mention above the hard way, after inspecting plants, the contents of the boxes too infrequently.

Another thing to consider with transparent boxes is the tendency of algae, including some species that you might really not want, and also cyano-bacteria to grow in such boxes if the bases are exposed to light. Therefore, consider shielding the bases in many situations with aluminum foil wrapped up to the soil or planting medium line. If sunlight is to shine on the box during warm weather, avoid dark foils and avoid black paper, unless your objective is to cook the plants.

I acknowledge that there are some plant genera and species that would not do so well with too much light getting into the pot sides...so shield those roots from light with something that reflects light, unless you have a particular reason to need to warm up the roots. There are plenty of plants that like that, too, but don't let them reach cooking temperatures, which can be as low as 65 degrees for some species that I've grown or well over 100 degrees F for others. Get to know your plant's requirements, first. Some will want lids on the boxes and some won't.

Another point well made in response to the original question was that one can often use recycled containers. I have found reasons to use 1/2 gallon plastic milk boxes on their sides, plastic clam shell produce boxes, both those with ventilation slots and those without same, plastic meat boxes that have fitted transparent lids and black bottoms, etc. I have used cupcake boxes, both new and recycled, plastic cake boxes, etc. I only buy the new ones for use as very large community pots or very large germination flats.

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