Print

[Auxin]

So I read about mixing used coffee grounds into potting soil for tea plants, to help with drainage and aeration. One thing I'm not clear on, after washing out the oils and such does the soil/grounds mix need to age for a month or can it be used right away?
Will fresh coffee grounds promote rotting?

[XDX]

I think it depends on the plant type...
and what ratio of coffee:soil- i think i use somewhere between ~2-10% coffee grounds, depending on the plant. just a guess, i hardly ever measure things....

in my experience, i dump fresh spent coffee grounds on top layer of potted plants. i get a flush of new growth, nice deep green color, but it seems relatively short-lived. it helps to kind of mix the grounds into the soil layer though, rather than let it build up on top. when it builds up, the coffee doesnt rehydrate well, and causes uneven watering issues, similar to coco fiber that has dried all the way- the water just rolls off the top, or drains but doesnt absorb. very rarely, if built-up coffee grounds stay wet too long, they can start to grow some molds-i dont think its harmful to the plant, i think its breaking down the coffee into more usable material for the plant, but i generally consider it not attractive nor ideal when mold sporolates indoors
using strait coffee grounds mixed in soil can help with draining, but too much can also make it hard to hydrate evenly. mostly i use it to drop the pH a lil and short burst of N.

Using composted coffee grounds is probably better all around, because i think it will hydrate more easily, mold less easily, and still provide good N source. and might be less acidic (not sure), which might be more desirable sometimes. but idk if a month is long enough to cause much change, unless expedited using worms or fungi or similar. If I fully compost grounds for 6mo-yr (usually goes a lil more anaerobic than i would like, but w/e), the coffee grounds will become thick dark black mud, something a kin to "mushroom compost" sold at stores, which i think is very rich in nutrients, but will now need to be amended for good drainage.

I mostly use coffee grounds (fresh and composted) on plants of Solanaceae and Ericaceae, as well as aya vines, fairly generously. with other plants such as slower growing tropical fruit trees, i usually mix a little in the top layer of soil once or twice a year. and then things like cacti and succulents, i hardly use any at all.

4 Likes Auxin, BubbleCat, plantlight and danzick like this.

[danzick]

Great practical information.  Thanks XDX!   

[BubbleCat]

Obswrve coffee pouring out of a coffee maker. The first portion will be very strong, it will begin to thin out until what comes last is barely anything but water. Add too little coffee and this last portion will grow and dilute te whole product to forma very light coffee. So you can assume that brewing coffee almost completely leeches out the coffee grounds.

Further composting it would break down whatever organic matter is left by means of microorganisms feasting on it. This includes oils.

I can not tell for certain but I wouldnt believe that even considerable amounts of uncomposted coffee grounds would harm a plant. Plants can deal with some amount of oil. Other things in there that might be of concern is what has been transformed during roasting. Again, remains of a fire, charred organic matter and such dont hurt a plant. You might have trave amounts of caffeine left. It is a plant product and remains mobile in plants. So your plant will pick it up. I do not think caffeine, especially in small amounts, would hurt a plant, even if it doesnt naturally produce it, much like you can spray aplant with nicotine, another nerve poison, and it will end up in the plants system and even benefit it. So again: I dont expect harm from teacea of caffeine, if any I could imagine positive effects.

The only thing that wpuld concern me is: Keep an eye on the percentage of organic matter in the mix for a type of plant, for most plants the share of organic matter shouldnt exceed a specific value.

Correct me if I'm wrong.

1 Like Auxin likes this.

[Auxin]

Right on, I'll just use as-is.
For some odd reason my town didnt get any good potting soil this year. The 'best' I found in any store was almost pure peat, lol
20% coffee grounds improves the texture so much, and tea plants like it around pH 5 anyway 

[nobody]

I sun dry coffee grounds then add them directly to my potted plants. Sun drying them, on an old shirt or something that drains, seems to cut down on any pH spike from the first watering. Other than nutrient help, coffee seems to be a great option if you have any issues with root mealys or other soft bodied root insects.



nobody

1 Like Auxin likes this.