AFAIK, in Theravada, ordained monastics are prohibited from growing their own food. Even hydroponics would likely be prohibited by vināya due to probability of harming small unseen life (algae, etc) in maintaining a hydroponic system.
Are there any ethical concerns for Buddhist laity, including those moving towards but not yet fully ordained, especially from a Theravada perspective?
As a side issue do ordained monastics maintain houseplants or gardens, or outsource this work to laity?
There is no prohibition for laypeople to involve farming activities. There are some wrong livelihoods for a layperson, but farming is not one of them. Theravada monks are prohibited from involving in any farming activity.
As a lay person, I grow food both hydroponically and in the garden. I also study the suttas and have found nothing contrary to these practices. Indeed, I have found quite the opposite. The following quote from the Buddha resonates totally with "No-Dig" in permaculture
MN81:18.12: He’s put down the shovel and doesn’t dig the earth with his own hands.
The Buddha was quite familiar with agricultural practice:
SN22.54:1.2: “Mendicants, there are five kinds of plants propagated from seeds. What five? Plants propagated from roots, stems, cuttings, or joints; and those from regular seeds are the fifth.
In that very sutta, the Buddha continues with the agricultural metaphor, and almost addresses hydroponics with its lack of reliance on soil:
SN22.54:1.5: Suppose these five kinds of plants propagated from seeds were intact, unspoiled, not weather-damaged, fertile, and well-kept. But there’s no soil or water. Then would these five kinds of plants propagated from seeds reach growth, increase, and maturity?”
SN22.54:1.7: “No, sir.”
Notably, in my own hydroponics, I actually do use soil with great benefit, but that's a separate discussion.
The suttas are rich with agricultural metaphor and farming certainly is not included in the lists of wrong livelihoods given in DN1. That list, for example, does include accounting(!), but does not include farming.
DN1:1.24.4: Such is an ordinary person’s praise of the Realized One. ‘There are some ascetics and brahmins who, while enjoying food given in faith, still earn a living by unworthy branches of knowledge, by wrong livelihood. This includes predicting whether there will be plenty of rain or drought; plenty to eat or famine; an abundant harvest or a bad harvest; security or peril; sickness or health. It also includes such occupations as computing, accounting, calculating, poetry, and cosmology.
Even if a lay person aspires to become a monk, experience with farming itself provides a valuable introduction to the terminology of the suttas. In today's consumer world of newness arriving at our doorstep, we've lost the reality of our connection with the earth. In contrast, farmers know quite well the impermanence of all things and the role that a single seed can have as it puts forth roots and matures. Teachings such as the following are imbued with real meaning born out of that very personal experience with farming:
SN42.11:3.6: For desire is the root of suffering.’
