I wouldn't add coffee grounds at all. Indoor plants rarely if ever have soil pH issues, so adding acid isn't going to cure anything, and coffee grounds will break down into fine, small particles that will impede drainage and suffocate roots. Plus the caffeine will make them irritable and jittery, not that you'll be able to tell. (Joke.)

There will be differing opinions presented here, I can just about guarantee, but still: I wouldn't if I were you.

I agree with the PP. There are many more good reasons to avoid using coffee, tea, and coffee grounds in container culture than to include them.

Al

I see I should clarify my question - I don't intend to use coffee grounds, I just want to know how often those people who do so are pouring cooled down liquid coffee onto their houseplants.

thanks for the tips, though; I'll remember that in case I was going to get a wild hair...

I think your question was clear enough - I just wouldn't include coffee OR tea, nor coffee grounds as any part of container culture. ;o)

Al

Cooled coffee is probably okay, though I doubt it's necessary. I think I've seen the claim (probably true?) that coffee is approximately equivalent to a very, very light fertilizer (like 0.2-0-0 or something). But I don't know that there's any compelling argument to be made in favor of doing it, or any reason to do it more often to some plants than to others.

I have reported elsewhere, long ago, that I had a Sansevieria in an office that got nothing but leftover black coffee for 13 years and it did just fine for an office plant. [The link has further discussions by other persons too.]

After retirement I took it to a better location and started watering and it put off pups as would be expected.

A man can survive a good long while with coffee as his only liquid intake, but does the fact that he survives make it wise? Similarly - that a plant survives a particular watering regimen with coffee is no testimony to its benefit.

From a recent post: "There's a lot of conversation on the forum lately about adding dilute coffee/tea to plants. I replied on one thread & got beat up pretty bad for offering the reply, but Arabica (coffee) and Camellia (tea) are known for their toxic alkaloid (caffeine) content and their allelopathic affect on plants as well as autotoxic (to their own seedlings) effects on future generations. Caffeine interferes with root development by impairing protein metabolism. This affects activity of an important bio-compound (PPO) and lignification (the process of becoming woody), crucial steps for root formation.

We also know that the tannins in both coffee and tea are known allelopaths (growth inhibitors). There are ongoing experiments to develop herbicides using extracts from both coffee and tea that cause me to want to say they might serve better as a nonselective herbicide than as a tonic. I would not use either on my plants."

Al

The thing is if you drink a lot of coffee and wish to make use of the grounds....or tea leaves if you are so minded...then throwing them into your compost is what you should do.
An expert I acknowledge knows something about horticulture suggests since houseplants like a little acidness, then giving them some diluted coffee or tea every 3rd or 4th watering will be liked.

If you accept the fact that coffee and tea are acidic, then you have to believe that feeding them occasionally what acidness they can and what acidness you believe the plant might appreciate, then you will make a habit of watering with the addition of such at intervals.

To give a plant at every watering such pH enhancer is I think going overboard. With so many proper fertilizers at hand, coffee and tea should be left on the table to stain the cups they're in.