Zoreiah 11 (Klal 11 Siman 4) Hilchos Shabbos - S0342

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We are continuing in siman 4, where we learned about the concept of a flowerpot with a hole. The hole makes the flowerpot considered connected to the ground, so placing or picking up the flowerpot from the ground will be zoreiah or kotzair, respectively. 

Next, we need to discuss a vessel which has no hole, but is made of material which may allow for absorption. On the one hand, there is no hole, but on the other hand, the plant still may be able to absorb from the ground.
The Chayei Adam writes that this question is a machlokes. One opinion is that earthenware vessels are not a barrier to the ground, since they are from the ground themselves. Another opinion is that wood should not act as a barrier since wood is a material which grows, so it inherently allows for the absorption of nutrients. On the other hand, this opinion holds that earthenware is not alive, so it will serve as a proper barrier.
The Chayei Adam writes that this question is a question of an issur deoraysa (kotzair or zoreiah). Therefore, one should be machmir. 
It is important to note that Rashi and Tosfos understand that the concept of a flowerpot with a hole absorbing nutrients from the ground is not deoraysa, but an issur derabanan that Chazal extended since it approximates the issur. If so, one could argue to be meikil. However, the Chayei Adam follows the approach of the Rambam, that this case is a question of a safeik deoraysa, and therefore one cannot be meikil.

Summary
It is possible for a plant to absorb nutrients from the ground without directly touching the ground. Therefore, removing a plant which was already absorbing nutrients in such a manner is kotzair, and placing a plant to absorb nutrients in such a manner is zoreiah. 
Similarly, these halachos apply to materials which are porous, such as earthenware and wood.