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I was told to add coffee grounds to my blueberries. After I did the leaves on two of them turned dark red and they all fell off. Leaves have returned and loads of flowers, but the berries seem to not be developing well. It is also about a month after my berries should have been picked. I am in Largo Fl. Is this due to coffee grounds and why?

Jeff T
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  • I have no clue about the blueberries, because I'm new to them this year, but I can tell you that they recommend fertilizing Nepenthes with coffee, because it helps acidify the potting media and add trace nutrients. I'd assume it's doing the same thing for the blueberries on a larger scale as they like acidic soil. – Dalton Mar 22 '16 at 19:28
  • I had the same issue although I did not put coffee grounds. My leaves turned dark red and fell off and eventually the plant died. – JStorage Mar 22 '16 at 20:54
  • What season did you apply the coffee grounds, and does your plant normally drop leaves once a year? – Graham Chiu Mar 23 '16 at 18:32
  • Did you also test the soil pH before doing this? – Graham Chiu Mar 23 '16 at 18:33
  • Blueberries need boat loads of water to thrive, the soil need to drain well because they don't like to sit in water, but they do need to be watered a lot and often. I am not telling you to water them some more, but are you aware of this and having you watering them enough? Under watered blueberries bushes will turn red. – Escoce Mar 30 '16 at 14:09
  • It sounds unlikely to be an under watering issue if he has lots of new leaves and flowers. But small berries does sound like a lack of watering. – Graham Chiu Mar 30 '16 at 20:22

2 Answers2

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Reddening of the leaves of blueberry plants can be caused by a lack of phosphorus. Although coffee grounds contain phosphorus, they are also highly acidic. If your blueberry plant were already in acidic soil as it should have been, you could have made it even more acidic rendering phosphorus insoluble and unavailable to the roots.

Nitrogen (N), Potassium (K), and Sulfer (S) are major plant nutrients that appear to be less affected directly by soil pH than many others, but still are to some extent. Phosphorus (P), however, is directly affected. At alkaline pH values, greater than pH 7.5 for example, phosphate ions tend to react quickly with calcium (Ca) and magnesium (Mg) to form less soluble compounds. At acidic pH values, phosphate ions react with aluminum (Al) and iron (Fe) to again form less soluble compounds.

http://www.nutrientstewardship.com/implement-4rs/article/soil-ph-and-availability-plant-nutrients

That's why it is suggested that if you're adding a lot of coffee grounds to your compost pile, you also add some agricultural lime.

Graham Chiu
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One teaspoon of sulfate of ammonia to 9lt of water water twice a week.

Jared Blackburn
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  • Jared, welcome to Gardening SE! Please note that Stack Exchange and its sites works differently from the standard web forum you may be familiar with: we have a “one question - multiple answers” format and each answer should a) answer the question and b) be phrased so that it works alone. It’s also a good idea to add “why”as and a bit of explanation to an answer. I suggest you take the [tour], browse our [help], especially [answer] and then consider an [edit] to add a bit more details. As it stands, it may get more downvotes and possibly even be removed by the community. – Stephie Jul 18 '18 at 18:58