Effectiveness: Hard to judge
Once in a while I clean my coffee machine by ‘brewing’ a batch of water without using any new coffee grounds. I’m left with a pot of coffee-infused water.
I don’t like pouring perfectly good water down the drain, so I wait for it to cool, then water my plants with it. It’s easy to pour, and it will give plants an ‘extra shot of nitrogen and acidify their soil a little.’ That’s assuming the plants want their soil to be acidified. Many don’t.
Plants that love acidic soil include ferns, cilantro, lemongrass, gardenias, rhododendrons, magnolias and foxgloves. Stinging nettles also love acidic soil, but I can’t stand those things. You might think I’m really knowledgeable because I just pumped out that list, but actually I got it from this very thorough site. Judging by the list, most plants that like acidic soil originate from Asia.
It’s hard to tell how effective this really is. I’ve been watering all of my plants this way, when I should have been sticking to the ferns and cilantro. Next time I’m going to give the whole pot to the sad-looking ferns in my bedroom.