I made three planting media: commercial potting soil, straight coffee grounds, and a half and half mixture of the two. In one test, I took some marigold seedlings that I had started in a paper egg carton and transplanted them into 4 inch pots containing each of the planting media. In another test, I started seeds of: tomato, kale, broccoli, chard, and lettuce in paper egg cartons, using each of the planting media.
The marigold seedlings in the various planting media showed a similar growth rate. The plants in the coffee grounds had a purple color to the outer (older) leaves. Those planted in commercial potting soil had green leaves, and those planted in 50:50 coffee grounds:potting soil were almost exactly intermediate between the other two.

Of the seeds, only tomatoes showed 100% germination. In every case, the seeds planted in the commercial potting soil germinated first, followed by those in the 50:50 mix, and then by those in the coffee grounds. In the tomatoes, the differences in germination times were within a day. Other plants showed more variation. The broccoli, kale, and lettuce showed little difference in germination success between the potting soil and the 50:50 mix with 91% and 89% of the seeds germinating. Only 61% of the seeds planted in coffee grounds germinated. The chard is slower, but seems to show the same pattern. The seedlings in each of the planting media appear equally healthy as the first true leaves appear.

Not surprisingly, commercial potting soil works better than coffee grounds in supporting seed germination. However, mixing this half and half with coffee grounds has little effect on the germination rate. Tomatoes germinate as well in coffee grounds as in potting soil.

I have one success that I forgot to report because I had given the plant to someone else. I put a Bougainvillea in a pot of coffee grounds about three years ago. It is thriving as well as we would expect for a Bougainvillea in a container that is inside half the year.

Nandina,

I've been here only a year and a half, and started putting coffee grounds on the ground within a week of my arrival (more fun than unpacking). I have hoped that coffee grounds would prove unpleasant to nematodes, and so far I have no confirmed nematode problem. I do have a couple of area where plants don't seem to do well, but I don't know that it's from nematodes.

Of all the seeds I started, only the tomatoes seemed to do as well in coffee grounds as potting soil. I looked at the tomato seedlings today and those in the coffee grounds appeared to be the largest.

I also recently put some cuttings in coffee grounds. We can compare notes in a few weeks.

You can actually buy coffee grounds if you have money to waste. (Copy and paste the following link into your browser's address bar)
http://growjoeplantfood.com/coffee.html

Also, I thought you might be interested in this:
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Posted by: lil_Rhody z6b RI (My Page) on Sun, Dec 29, 02 at 8:28

WOW! after a little effort in research I found this:
"Caffeine is present in coffee and cocoa beans to protect the plant against harmful insects, but it is pure chance that it has a toxic effect on molluscs (slugs). Researchers say that they do not know why caffeine killed the slugs. But they suggest it may act as a neurotoxin, since exposed slugs fell to "uncoordinated writhing" before dying. It could be very useful because coffee is not likely to harm people so it's far better than spreading the traditional products, which also harms beneficial insects."

Source: New Scientists
Journal reference: Nature (vol 417 p 915)

"After you brew your coffee, save your grounds. Put them in a canister like an ice cream bucket or coffee can. Scratch them into the soil. Coffee grounds are an excellent fertile source of organic matter of plant food. They contain about 4% nitrogen, 1% phosphorus, and 3% potassium. You can also dilute your coffee grounds with water. This makes an excellent liquid fertilizer that's completely organic. Keep in mind, coffee grounds are acidic, so you want to be careful how much you apply to the soil."

Source: Rebecca's Garden
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I disagree with the statement that coffee grounds are acidic, but otherwise, I thought the passage was useful.

http://www.starbucks.com/aboutus/compost.asp

1982-1994 Had a Sanseveria (? S. kerkii) in an office cubicle that was "watered" with nothing but black coffee, about thirteen years.

c.1992-1994 Transplanted tall single flowered marigolds into a planter of coffee grounds; were more red-orange than the same in soil.

1997 Planted a rooted Ficus benjamina cutting in nothing but coffee grounds as a planting medium. It is still thriving.

1998 Did the Bougainvillea mentioned above in this thread. It is still doing alright as far as I know.

2000-2003 Transplanted annuals into pots with coffee grounds as a planting medium; snapdragons, Martha Washington [whatever] and an unknown with tiny white flowers. They all thrived.

During this period I did the cottonwood seedlings. The one in coffee grew faster and larger, the control in soil grew slower and stronger.

Midwinter rooting of hybrid poplar cuttings in coffee grounds was a success.

Starting annual seed in coffee grounds has not been successful to date.

Attempts to root common veining houseplants that will root in water, a pathos(?) and the one with the purple and silver leaves have not been successful; but the latter will live in dilute coffee once rooted.

I am currently growing an Iris in coffee grounds.

Note: in each case above the coffee grounds had been accumulating in a container under the sink for months i.e. none or fresh. I wonder if that matters.

The excresso grounds form a hard crust around a bundle of "mud" in the middle of the pot. I just broke open one that had been setting in the sun on a deck since August and it still had mud in the middle.

My conclusion, expresso grounds must be treated differently in experiments to use them as a planting medium.

Is there a problem with mould on coffee grounds other than people seem to abhor moulds except in blue cheese?

I have limed and flushed plenty of clean water through to fix the problem. I had been feeding them liquid seaweed and coffee grounds, both of which can have a high level of manganese (see: http://www.ithyroid.com/manganese.htm), and coupled with a low pH can result in purple lower leaves, particularly along the veins. These plants have subsequently fruited profusely so I'm thinking lack of phosphorus is not a problem!

So If you're using coffee grounds, make sure you check the pH of the potting mix or soil and keep it from becoming too acidic, using lime or crushed egg shells (http://www.backwoodshome.com/articles/nyerges44.html).

Gena, people who mention tea bags usually don't give much additional information. Were I to get a gallon of tea bags I might try another Ficus cutting in just tea bags. I would expect it to grow and thrive if not given too much attention.

Use it if you got it - cautiously. Be careful and watch what happen and there will be no problem.

Coffee is and expensive way to get benefits unless you have to deal with waste or you are into helping Starbucks deal with their waste. Don't spend money on coffee hoping to help your plants somehow.

I was wondering if anyone can recommend a plant that might be well suited to growing off pure coffee and in the dodgey English spring-summer time!

many thanks!