Yes, they will mold.......anything organic will mold as it begins to decompose but that is of little concern to the plant. Certainly no reason to scrape off the fertilizer (which is also derived from organic materials).

But you want to be very careful in what sort of organic matter you add to container/potting soil. The best container soils are created from very durable, unlikely or very slow to decompose ingredients. Adding things like coffee grounds, compost, worm casting, etc. can alter drainage to the point where it raises the perched water table and slows drainage significantly. This leads to root rots and other disease issues. Not to mention that container soils do not contain the populations of soil microorganisms necessary to breakdown these organic components properly and release the nutrients to the plants.

Keep the OM for inground plantings. And the dry organic ferts like Rose Tone. That's where they belong.....not in containers :-))

I agree with gardengal48 (PNW Z8/9)....

Plant as you'd normally do, except leave a bit more "lip" of the pot at the top. If you want to add coffee grounds, put a layer up to an inch thick on top, then cover with another inch or two of mulch. Make sure there's still between a half and one inch between the top of the mulch and the rim of the pot.

I put my pots directly on the ground (or deck, if that's where I have them). Doing so, I always find earthworms in my pots. They seem to be attracted to the coffee grounds -- which I used as I described above -- and they pull them down from below.

Having experimented with coffee grounds for a few years, I've come to the conclusion that they do best when covered with mulch, or if repeatedly added lightly on top of mulch so that it filters down. I used to pile them on thick in the garden, and things worked fine, but I later found that once dried and crumbly, those grounds became like sand and took a lot of water to get wet again. That was fine for things with their roots far below, but shallow-rooted perennials and self-seeding annuals started fading away from thirst. Elsewhere, I piled the grounds on thick and covered with mulch. There, the grounds never dried out, and became "black soil" more quickly.

If I'm able to resume my daily collections from Starbucks, I'll be sure to be layering coffee grounds and mulch from now on. From what I've seen of the improvement in my garden, these two ingredients are enough to make for amazing garden soil. You could speed things along with some dry organic fertilizer and/or alfalfa meal now and again, but it wouldn't be necessary.

:-)

~Christopher

I read on another thread here that coffee grounds aren't good for the plants. Can't remember why. I used to put lots on...this year I'm hesitant. ???

Also, Garden Gal - did you mean that the Tones aren't good for potted roses...only in the ground? I bought some Plant Tone this year.

Carol

Carol I think all the organic matter in your rose pots seem to be successful.

Carol, I find worms in my containers as well and add myccorhizal fungi when I pot things up, and later on I use molasses for the organisms so as not to compete with each other and cancel each other out. The mycorrhizae do indeed make the roots take off, because when I repotted my tiny gallon EA rose from being potted up at the beginning of April, it's roots were to the edge of a half barrel and very thick. I use rosetone in my pots because I hopefully have created an environment in the pot for it to be broken down properly.

roseloverinsf I heard coffee grounds aren't good to use directly on the garden in some circumstances; so I have since started composting in a cheap garbage bin with the coffee grounds instead. I have acidic clay soil and coffee grounds CAN be highly acidic if not washed properly before distribution. My soil had zero nitrogen when I tested it so I wanted to use coffee grounds but that's not how it works in soil as opposed to composting. Everyone has different preferences and it depends on your soil and plants. It depends on your soil, because like me, for instance, my soil is already highly acidic in some areas that adding more acidity could prove toxic to my plants. Again, it depends on your plants too, do they love acidity? Coffee grounds don't add nitrogen to the soil I have heard. They only help with aeration and help with adding organic matter to your soil.

Wow....lots of information...I'm not good at understanding these things. LOL I get soil that is this:

is comprised of a combination of black loam, peat loam, very-well-decomposed manure and a touch of mineral soil. These ingredients encourage microbial activity, which aid in plant growth.

What do you think of this soil for containers? Would Plant Tone (which I just ordered (sigh)) be okay for that? It sounds like the soil I use has too much organic matter? Which to me makes no sense :)

Carol

Thank you for all your responses! I just asked the questions about coffee grounds because I have them daily from k cups and thought of using instead of just throwing them away in the trash.

My roses live in miracle gro potting soil with no amendments. They have never been repotted or the soil replaced/added on. I wet fertilize them with miracle gro (bloom booster or all purpose) to replenish the nutrients. There are no earthworms as far as I can see. Maybe a couple of earwigs at best. I thought of adding organic matter through the coffee grounds until I can repot the roses. More as a pot filler than as nutrient source.

Considering all your highly informative and enlightening responses, I came to the decision of going ahead and putting the coffee grounds in the pots. They are in tiny portions (k cup size) that hopefully, soil pH change (if any) will be negligible and soil crusting will not occur. The soil environment is not sterile so the coffee grounds should somehow decompose in time.

Carol, the soil you describe is perfectly fine for growing plants in the ground. It is not at all good for growing plants in a container :-))

I could go into a long dissertation about what makes a good container soil but it has all been discussed thoroughly and is best presented in this very long running thread from the Container Gardening forum - Container Soils and Water Movement. The author, a GW member, is a well-known authority on container gardening, has numerous publications addressing this topic and is considered an expert in his field.

The 'water movement' portion of that discussion is key. Water moves through a container much differently than it does in the ground and does not have access to the free and widespread drainage you will encounter in most inground soils. So fast drainage and good aeration are critical to the success of a container planting and you cannot get that with regular garden soil and lots of OM. Part of it has to do with particle size - ground soil has too fine a particle size for a limited drainage situation like a container - and part of it has to do with the decomposable nature of organic matter. Compost or manures (and worm castings, coffee grounds, etc.) will continue to decompose and become smaller and smaller in size until they are so small, there is no longer sufficient pore space (voids) between the particles and this adversely affects both aeration (oxygen penetration) and water movement/drainage. They will eventually turn into what is essentially a mucky, wet sludge.

A good container soil has both texture and durability. Texture is the size of the individual particles that make up the soil and durability is their ability to resist decomposition. An ideal potting soil is something like the 5-1-1 mix or 5 parts composted bark fines, 1 part peat or coir and 1 part perlite or pumice. And while both the bark and the peat are considered organic matter, the peat is already fully decomposed and the bark will hold up for years with minimal further decomposition.

Other organic matter is a great amendment to add to garden soils but is not appropriate to a container situation. That's one of the primary concepts that differentiates container gardening from inground gardening. Just get that "OM is a good thing" concept out of your head :-)) In a container it is NOT!!

Okay. I understand now. I am very grateful for your summation. I can't afford to redo my 60 roses in pots...but I will do your method from now on. Thank you!

Thank you roselover for letting me bump into your thread.

Carol

Gardengal - will you please check out my post in container gardening. :) I have a few more questions. Thanks!

Carol

I want to iterate when I had said coffee grounds are acidic what I had clearly stated was coffee grounds that are NOT rinsed properly. If they aren't rinsed they do test highly acidic. There was a research paper I had read and a study done on coffee grounds changing the ph of soil, and when they had said in their findings that the coffee grounds were not acidic they were referring to coffee grounds that were thoroughly washed and rinsed. When washed and rinsed well they do not change the ph of soil. They also said when NOT washed they tested very low on the ph scale and were HIGHLY acidic. Also when I said coffee grounds help with aeration in soil, in no way was I meaning that towards use in containers! Sorry for the misunderstanding, but what I had mentioned had to do with soil that does not have good aeration like clay soil IN THE GROUND not in containers. Coffee grounds are organic matter and do help with aeration in clay soils, as adding any type of organic matter helps with the aeration of clay soils. Whether that is applied moderately and directly to the garden and then broken down by worms and weather, or added as an ingredient to compost; it does the exact same thing in the end by adding organic matter to the soil.

Why are coffee grounds highly acidic if not rinsed? Grounds CAN be acidic because its like feeding your plants liquid coffee. Which liquid coffee is very acidic. Them not being rinsed and then adding water to your garden makes coffee. Well, you get the point I assume. So hopefully that clears up the information I had provided you.