Why is topsoil specifically "NOT FOR CONTAINERS"?

May 17, 2020 5:58 PM

I'm trying to buy some dirt to fill holes in my yard, and multiple products on bigbox.com that are marked "topsoil" have specific warnings that say "NOT FOR CONTAINERS". Why would that even be a thing? Does something awful happen if you put topsoil into a container?
posted by mccxxiii to Home & Garden (8 answers total)

Best answer: Potting mix for containers generally has perlite in it to stop the soil compacting. Topsoil does not, so may just become compact and poorly draining in a container. Not a big deal, but it's not optimal.
posted by Jimbob at 6:20 PM on May 17, 2020 [6 favorites]

Best answer: Topsoil is wicked heavy and as JimBob said it will compact, making it difficult for plants to root and for the containers to drain properly.

If you can't get perlite for some reason: if you have some lightweight material, like dried grass clippings, mulch, etc. lying around where you live (or you can get hold of it), you can mix that in.
posted by Sheydem-tants at 6:31 PM on May 17, 2020 [1 favorite]

Response by poster: That's good info, thank you! I actually DO need it to compact so it will fill up these holes, so I guess I'm on the right track. :)
posted by mccxxiii at 6:32 PM on May 17, 2020 [1 favorite]

Best answer: Too much compaction the roots of your plants will not have enough oxygen to thrive. If the topsoil isn't full of clay you can add sand and/or spent coffee grounds. The grounds for extra nitrogen.
posted by Arctostaphylos at 7:49 PM on May 17, 2020

Best answer: It probably says it in such big letters because the stuff is way cheaper than potting soil etc., and therefore looks very tempting if you don't know the difference.
posted by teremala at 7:51 PM on May 17, 2020 [2 favorites]

Best answer: It is a very different mix for different circumstances. It really will cause problems for potted plants if you use topsoil without knowing the ramifications.

Conversely, using potting soil in the ground can be okay because most soils are too heavy or too sandy/clay for bedding plants unless you are lucky enough to have good loamy rich soil. For bedding plants, I usually recommend mixing in compost or the equivalent.

To fill holes, topsoil is the perfect medium.
posted by mightshould at 4:37 AM on May 18, 2020

Best answer: Does something awful happen if you put topsoil into a container?

Yep, terrible if you're a plant. They grow at first and then wane in health.

(Seconding teremala that the big warning is because it's cheaper than potting medium.)
posted by desuetude at 8:45 AM on May 18, 2020

I can personally attest to the problem of topsoil in containers; it doesn't drain well and compacts to the point that many plants have trouble thriving in it. Mixing 1:1 with proper compost will make it behave more like what you want.
posted by aspersioncast at 5:12 AM on May 21, 2020