There is nothing wrong with putting flowers, plants and tree seedlings in bathrooms, so long as there is no extravagance or waste involved in that, both of which are blameworthy. Allaah says (interpretation of the meaning):
“And let not your hand be tied (like a miser) to your neck, nor stretch it forth to its utmost reach (like a spendthrift), so that you become blameworthy and in severe poverty”
This is a prohibition on both miserliness and extravagance.
And Allaah says (interpretation of the meaning):
“and waste not by extravagance. Verily, He likes not Al‑Musrifoon (those who waste by extravagance)”
“And give to the kinsman his due and to the Miskeen (poor) and to the wayfarer. But spend not wastefully (your wealth) in the manner of a spendthrift.
27. Verily, the spendthrifts are brothers of the Shayaateen (devils), and the Shaytaan (Devil‑Satan) is ever ungrateful to his Lord”
[al-Isra’ 17:26, 27]
Extravagance means spending too much money on permissible things, and waste means spending money on things that are inappropriate.
It is said that waste means spending money on things that are inappropriate and extravagance means spending too much on things that are inappropriate.
In other words, extravagance means overstepping the mark in spending money, and waste means spending it inappropriately, which is worse than extravagance. Hence Allaah says: “Verily, the spendthrifts are brothers of the Shayaateen (devils).”
And it was said that extravagance (israaf) is not just in terms of money, rather it applies to everything that is done inappropriately. Do you not see that Allaah described the people of Loot as being extravagant because they put their seed in a place that is not for tilling. Allaah says (interpretation of the meaning):
“Verily, you practise your lusts on men instead of women. Nay, but you are a people transgressing beyond bounds [musrifoon] (by committing great sins)”
And He described Pharaoh as being extravagant, as He says (interpretation of the meaning):
“verily, he was arrogant and was of the Musrifoon (those who transgress beyond bound in spending and other things and commit great sins)”
Then he said:
From these texts we learn that extravagance (israaf) is of two types: haraam and makrooh.
The first kind includes wasting money etc on things beyond the norm.
The second kind includes wasting something useful for no purpose, such as pouring away what is left of a drink of the water of the Euphrates etc without putting it back into the water. End quote from al-Furooq al-Lughawiyyah, p. 114-115.
See also Fayd al-Qadeer (1/50) and al-Mawsoo’ah al-Fiqhiyyah al-Kuwaitiyyah (4/176).
Examples of extravagance include: buying something decorative for hundreds of riyals, because adornment is allowed but paying a lot of money for it is blameworthy extravagance.
An example of waste is buying something that is of no value or that will not last, for a large amount of money.
This, like the example given above, comes under the heading of wasting money that is forbidden in Islam: “Allaah hates three things for you: gossip, wasting money and asking too much.” Narrated by al-Bukhaari (1477) and Muslim (593).
Conclusion: we must beware of both things and realize that wealth is a blessing that should be guarded; we will be asked about this wealth tomorrow: “From where did he earn it and on what did he spend it?” as it says in Sunan al-Tirmidhi (2416) from the Prophet (peace and blessings of Allaah be upon him).
We ask Allaah to keep us safe by His bounty and grace.
And Allaah knows best.