Planting for water purification
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I recently began working at a company that builds ecological swimming pools (eco pools) and ornamental pools. The water passes through large planters inside the pool containing tuff, gravel, and organic material where aquatic plants and ornamental plants grow (not edible plants), cleansing the water. These pools and purification systems are outdoors. Furthermore, there is a need for work in an open hothouse (roofless) to prepare new aquatic plant seedlings in special planters from existing shoots, and plant them in the pool garden.
It is possible that there will be a need to uproot plants around the pool to set up the pumps and replant them after the completion of the installation process. It is also possible that it will be necessary to plant flowers around the pools as well. In order to advance at work, it is necessary to commit to work for at least two years. I was wondering what the status of these melachot are during shemitah that will begin next year.
Your question contains several questions:
- Is it permissible to cultivate plants that will be used as a biofilter for pool water?
Halachically, this is forbidden since causing plants to grow is prohibited unless it is grown a detached platform with a roof above. Even if the plant is not grown for food or aesthetic appeal, rather for another use, the very act of causing it to grow during shemitah is forbidden (see Rambam, Hilchot Shemitah VeYovel 1:21). The only way to permit it is when detached platforms are used, indoors.
- What about plants that grew in a permissible manner, whose sole purpose is to strain dirt? Is it possible to put such plants straight into a pool?
In this case, one can be lenient, since the plant is not being planted in the soil, rather in a pool, which is an unperforated pot. Furthermore, there are sources that are lenient about planting in water (hydroponic systems). For this reason, it is possible to take plants used as filters and plant them in the pool. However, it is important to ensure that there is no soil whatsoever in the planters containing the roots of these plants (and to first wash off any soil stuck to the roots before placing them in the pools).
- Ornamental plants that are uprooted around the pool may not be replanted after the end of the work process and completion of the pool. Certainly it is forbidden to add more plants for aesthetic appeal, unless they are raised in a nursery and transferred with their clod of soil to a new location, set on a nylon sheet or a detaching surface. After shemitah they can be replanted into the soil.
- The most convenient possibility is to perform heter mechirah. If you are aware of future activities slated to be performed during the shemitah year, it is best to perform heter mechirah prior to However, it is possible also to perform the sale during the shemitah year itself (but it is complicated).
- You should check what it is possible to do, and based on this you can decide about working in this field.