Three Real Uses For Coffee Grounds And Gardening

Coffee grounds and gardening might not seem like a match made in heaven as there’s some evidence to show that we should be using this very abundant waste product in our gardening efforts.

And most of us have lots of this product so here’s how to work both ends against the middle and use this product.

The first thing to be aware of is there’s a lot of misinformation and unproven data out there about coffee grounds in the garden.

The Research on Coffee Grounds & Slugs

The research on slugs and caffeine shows that concentrations of caffeine as low as .01 % reduces feeding by slugs (they avoid caffeine treated leaves) but that it doesn’t kill them at that rate.

A 1% solution can be expected to kill 60% of slugs while a 2% caffeine solution will knock out 95% of all slugs. This 2% solution is more effective than the chemical normally used in slug control. (metaldehyde)

The 2% solution also damaged some foliage on the tropical plants being used to feed the slugs. This calls into caution the use of caffeine on more tender leaved plants.

So where does this leave you with your morning coffee grounds – and your garden uses?

Fresh coffee contains approximately .05% caffeine. Which is a heck of a long way from the 1% solution you need.

This means that coffee grounds and fresh coffee will not kill slugs.

Coffee Grounds In The Garden Mulch?


Used coffee grounds make an excellent mulch. Note that they are acidic with a pH of between 3.0 and 5.0.

BUT when they finish decomposing, they will be neutral (finished compost tends to be neutral) So they do not turn the soil acidic.

They can be used thinly all over the regular garden as organic matter so you can simply toss your used coffee grounds onto the garden if you like. Unless you’re adding inches of this stuff (in truckload quantities) to the garden, you’re not going to see a difference in your soil pH.

If you do add a massive quantity in one spot, you may want to dig them into the garden as there are reports that they will develop a fungal layer if left exposed to the air.

Coffee Grounds and Worms

Coffee grounds are beloved by worms. I used to have a worm bin and you could almost hear the cheer when I toss in the morning’s makings of used coffee grounds.

So if you have a vermiculture setup, use the grounds as a food source. If not, simply toss them onto the garden and the worms will find them.

Toss them out daily into the garden or into the compost bin to avoid fly buildups.

Composting Coffee Grounds

And they should go into your regular compost bin because they compost very well in the compost bin. They have a carbon-to-nitrogen ratio of 20:1, roughly the same as grass clippings. After making the morning wakeup, coffee grounds contain up to 2% nitrogen. So for composting purposes, consider coffee grounds “green” material similar to grass clippings.

And one of the interesting things about composting coffee grounds is that the microbes that do the composting will turn the coffee from acidic to a neutral pH.

So coffee does not make compost acidic.

So that’s all the real news about coffee grounds and gardening.

You can see all of Doug’s Ebooks here.

Doug’s Summary Notes

I hope this clears up some of the worst of the coffee ground garden rumours.

The one I hear the most is that the grounds will kill slugs or deter insects. If you get lucky, they “may” deter (and I wouldn’t even count on that) but they surely don’t kill.

But they are excellent organic matter to add to the garden.

Click here to read more articles about garden compost

What Can Go Into The Compost?

Questions and Answers About What You Can Compost

Image by Joke vander Leij Pixabay

What about composting leaves?

There are many recommendations that I have seen for composting leaves, putting them in green garbage bags for two years, making a leaf pile all by themselves, but I prefer a simpler way. I try to mow my leaves and then rake them onto the garden. I get a mulch with no work, and the worms and other soil microorganisms turn these leaves into great soil.
 But yes, you can compost leaves — they make excellent compost.

What about composting grass clippings?

Not this lazy gardener. I leave grass clippings, right on the lawn where they fall, so they’ll feed the lawn. A significant amount of nitrogen is in those cut tips, we want to leave those if possible to feed the grass.
 The only place to collect and compost grass clippings is in the South where the grass gross so quickly and there is a danger of thatch developing.

What about composting diseased plants?

The deal is fairly simple. If your plant is suffering from a soil-borne disease such as club root, then the diseased plant should not be added to the pile. If your plant has suffered from any other problem. It can be safely composted in a hot pile.

I note that the microorganisms in a compost pile will feed on the various molds, mildews and pathogens. They will simply not get them all. But most of these problems exist outside of a compost pile naturally, so we’re not really creating problems by adding small amounts of diseased material to the pile. Hot compost piles kill more than cold compost piles.

There are diseases that require living tissue to survive, e.g., tomato and potato blight, so these are fine to add to the compost pile.

Rule of thumb for beginners

  • If the root is diseased, don’t add to the compost
  • If it’s the tops, you’re fine.

What about perennial weeds?

Many of the very troublesome, perennial weeds require a very hot compost pile to kill them. These plants are so tough that cold compost piles simply gives them a place to grow. A simple trick is to dump all your perennial weeds (like pulled grass with roots attached) into a green garbage bag and tie it tight. Tuck the bag out of the way for a few months until the weeds are no longer recognizable or alive. Once they are truly dead, you can add them to the compost pile.

What about weed seeds?

Unless you have a very hot compost pile, do not add these. Mind you, I don’t know anybody who deliberately adds weed seeds to their compost. Weed seeds will not be killed except in very hot compost piles. I live with this and accept I’ll have some weeds from my cold compost bins. Don’t get bent out of shape by it — instead, put mulch on the gardens to stop the weed seeds from germinating.

What about hard stems or woody prunings?

You can add these materials to a compost bin, but they will not decompose quickly. They decompose better if shredded and mixed with grass or other high nitrogen materials.

Can I add animal manure?

Manure mixed with wood shavings should be composted until the shavings have decomposed.

Household pets such as guinea pigs and hamsters don’t produce a lot of manure,and while generally considered safe, I’ve never done this.
 Cat and dog feces should not be added to the compost.

Can I add sawdust and wood shavings?

These are very slow to compost; they are the ultimate “brown” or cellulose material and require significant amounts of green or nitrogen material to turn them into useful compost. Generally, we say don’t add them to compost piles.

What about tree trimmings?

Tree trimmings that have been chipped make an excellent mulch. As a mulch, they will slowly break down into compost. Frankly, I try to get as much of this free material as possible.

You’ll often see “Green ingredients” recommended for compost piles. Here’s what that means and what they are.

Green ingredients are quick to decompose and are high in nitrogen

  • Urine, diluted with water 20:1.
  • Comfrey leaves, nettles and grass clippings.
  • Raw vegetable peelings.
  • Tea bags, leaves, coffee grounds.
  • Young green leaves or weeds, avoid plants with seeds.
  • Soft green pruning.
  • Animal manure.
  • Grass clippings from lawn
  • Poultry manure.

Similarly, “brown ingredients” have their role in the compost cycle.

These are carbon rich or slow to decompose materials.

  • Cardboard such as cereal boxes and egg cartons
  • Waste paper or junk mail, I personally enjoy shredding income tax forms.
  • Cardboard cubes.
  • Glossy magazines. While these compost is often better to recycle them than compost.
  • Newspaper. This is the same as for glossy magazines.
  • Any bedding from veggie-eating pets such as rabbits or guinea pigs.
  • Tough woody clippings. Note these will compost faster if chipped up with a shredder
  • Old bedding plants.
  • Sawdust or wood shavings.
  • Leaves in the fall.
  • Other things you can compost.
  • Very small amounts of wood ash. Very small.
  • Hair.
  • Crushed eggshells.
  • Natural fibers such as 100% wool or cotton

If you have questions about Compost, I wrote an ebook answering the most commonly asked questions. Check it out here

How To Make Your Own Grow Bags of Compost

Yes, you can use old pantyhose or garbage bags to make your own grow bags. Here’s how.

OK, so it’s silly season in the greenhouse research area.

Use Old Pantyhose

Some researchers have taken old nylons (looks to be about that size anyway) filled them with compost to make their own grow bags and started growing in them.

Their results indicate that this indeed might be a good way to grow plants. They state that this might work in areas where there is no soil.

Ah yes. We’ve been doing this for years folks.

Use Green Garbage Bags For Inexpensive Grow Bags

I used to grow tomato plants in green garbage bags back in the early ’80s because I couldn’t afford the fancy grow-bags.

Lay the bag on the ground, fill it with a minimum of 12 shovels of soilless mix and away we’d go. After the crop was done, pick up the bag and old stems (carefully because it would be wet) and dump it into a compost pile for recycling onto the garden. Re-use the bags if they were OK (hey, they cost me a dime each!) :-). This was inexpensive gardening using what we had.

I’ve even taken bags of soilless mix (the 30-litre size) cut a hole in them and grow on the greenhouse floor rather than ground. This was rather more expensive than the old garbage bags but I wanted to see if it was workable. (it was).

Poke holes in the bottom of the plastic bag to allow the water to drain.

Real soil or potting soil in bags does compact so if you want to try this, stick to the peat-based soilless mixes.

If you’re looking for container gardening tips, click here

Put the garbage bag in a funky container

Image by RitaE from Pixabay

Can you use straight compost as a growing media?

Yes, you can *if* your compost is fully composted.

If it is not (or you’re in doubt) then only use it at 10% of the total volume of the soil (in other words, 1 shovel of compost for every 9 shovels of a peat-based soilless mix).

Fully composted material is fine — partially composted material may contain too many salts and burn tender seedlings. Here are the posts on how to make compost

As always, if you’re not sure try growing some tomato seedlings as they’re the most sensitive plants in the home garden. If they grow well, you’re fine.

But yes, a researcher has just figured this out. Good to know. And if you do have lots of extra old nylons around, you might give them a try. The only issue is to ensure you have adequate soil, support, and water for your intended crop.

Check out the other garden solutions on my Amazon ebook list here.

Why I Don’t Recommend Mushroom Compost

Mushroom compost is, in my opinion, one of the most over-hyped gardening products on garden shop shelves

Let’s examine the data.

How Are Mushrooms Grown

They’re grown on compost made specifically for this purpose.
This compost is made by mushroom producers from material such as

  • hay,
  • straw,
  • corn cobs
  • poultry and horse manure

Or any combination of organic material that is 1) inexpensive and 2) readily available.
Mushroom facilities do try to create a consistent compost so their production will be standardized.

  • The compost is made in large piles on concrete pads and when done, is loaded into dark buildings and mushroom spawn is sown.
  • The heat of the composting will kill off most weed seeds and other problems if it is done properly.
  • The mushroom crop is grown and normally 3 harvests are taken.
  • The spent compost is then removed, the buildings cleaned and sterilized and the process begun anew with the next batch of compost.

So – what are we left with.

What Are We Left With Afterwards

This is essentially organic matter

Research into using this material as a substitute for peat moss or other organic material in commercial nursery production systems have had to use a regular feeding system because the nutrient levels are too low to produce a crop.

If you purchase this material, you are not getting a nutrient level high enough to grow a good crop of plants.

There is also a high salt level in most spent mushroom compost that has to be leached out before the crop is planted.
General analysis of nutrient levels are (N=0.7% , P= 0.3% , K= 0.3% ) which is to say – negligible.

By contrast, bagged manure sold in most garden shops is N=1%, P=1%, K=1% (bagged manure has approximately 3X more nutrients than this compost)

You will not get a major nutrient benefit from mushroom compost.

Will Mushroom Compost Burn Plants?

See the “high salt level” above so if it’s not leached out and you pile it around a salt-intolerant plant, you *may* see some burning.

That’s a lot of “ifs” I understand, so if you purchase some, let me suggest you turn the hose on it to soak it and drive any salts out the bottom. I also note this will reduce the N (nitrogen) level of the compost significantly.

Chemical Residues

Mushroom farmers have major problems with flies and fungus gnats in their growing facilities and are licensed to spray regularly with such products as methoprene, cyromazine and diflubenzuron, Dimlin and Diazanon.
There are also fungal infections that can wipe out a mushroom crop and require control by such chemicals as benomyl, thiabendazole, and chlorothalonil.

Naturally, if treated with any chemicals or having used any kind of artificial nutrient to create a composting action, mushroom compost will not qualify for use on certified organic farms.

Some of these chemicals are what is termed “persistent” in that they do not break down quickly or under microbial action.

Leaf Compost Versus Mushroom Compost

Finished compost from any source has “roughly” the same nutrient content. There are differences to be sure but for the most part, I use compost as organic matter to feed soil microbes. In other words, organic matter feeds soil microbes which in turn make nutrients available to plants.

The major difference between the leaf compost you make yourself and mushroom compost is going to be in the chemical residues.


Every time I see this stuff for sale, it is sold at very high prices (often for fund raising ventures). Compared to the cost of a bale of peat moss or a bale of straw, spent mushroom compost is extremely expensive. This compost is not cost effective .

As with many things, readers have written to say mushroom compost is not expensive in their neighborhood. It’s a big world out there and I simply suggest you compare the cubic foot cost versus other organic matter.

I regularly get letters

I routinely get letters from mushroom producers saying “yes but”

  • Yes but – I know gardeners who use my compost and get great results
  • Yes but – I don’t use chemicals (or not many)
  • Yes but – you need to update your understanding of modern mushroom growing.

But not one of them can disagree with the chemical registrations and the fact that they are used in the majority of commercially produced mushrooms.

So yes, if you want to garden expensively and don’t care about possible chemicals in your garden – you can use mushroom compost.

Apply a lot of it and you’ll probably get a good looking but expensive crop of plants. The vegetables won’t be organic but as long as you don’t eat the flowers, they’ll look good.

Let me simply say this – if a mushroom producer is certified organic and is selling mushroom compost as certified organic – then I’d consider using it in specific situations if I required compost.

Without that certification, then my original message is the same. I assume it has chemicals, fungicides that will disrupt my soil ecology, and could be expensive organic matter when compared to other organic sources. As for the fertilizer value of this product, it isn’t close to other organic products in cost-value.

So nope, don’t recommend it. I write about the things I use and you can get those updates here.

What Do I Use Instead

I use compost made from our kitchen garden or garden wastes or composted manure from nearby farms. But most of you don’t live near farms so you’ll either have to make your own or use composted manure from local retailers.

For organic matter, I’m using old hay or purchased bales of straw as mulch in the vegetable garden. The ornamental gardens have wood chips we pick up at our municipal recycling area.

You can also create your own compost.

Compost Can Be Considered A Slow Release Fertilizer

The nutrient availability in compost is not going to be available quickly. As it breaks down over several years, it slowly releases its nutrients to the plants. If you need a fast acting fertilizer, let me suggest fish emulsion.

Here’s my ebook answering all the common questions and solving compost making problems.