Do you drink a lot of coffee? Those beautiful spent grounds look so lush and healthy, like fresh soil ready to grow giant tomatoes.
But what happens when you add them to your bamboo? Would it make a difference to add them to a bamboo patch versus in a pot? I wanted to know so I did some digging (pun intended).
Are coffee grounds good for bamboo? No, using spent coffee grounds directly in your bamboo patch or pot will inhibit its growth due to a phytotoxic compound in the grounds. Instead, compost the coffee grounds first using a standard compost pile or vermiculture. Then add the finished compost to your bamboo.
What Do Coffee Grounds Do For The Soil?
Coffee grounds, like any plant matter, adds organic matter and after they break down, nutrients to the soil. Until they break down though they actually bind up nitrogen.
A recent study found that spent coffee grounds (SCG) actually made things worse for the plant (source). Broccoli, leek, radish, viola and sunflower were grown in different concentrations of soil and coffee grounds (0%, 2.5%, 5%, 10%, and 25% SCG to soil).
In each instance that coffee was added plant growth was reduced. They weren’t able to attribute that directly to increases in pH or nitrogen being bound up.
Instead, they suspected it was due to phytotoxic effects from the coffee grounds. They weren’t able to devise exactly what compounds in the coffee had the phytotoxic effects.
The good news from this study though was that SCG in the study actually hurt weeds as well.
You can use SCG in the soil though. You just need to compost it first. Personally I compost all my coffee grounds and filters using red wriggler worms (vermicompost).
I’ll discuss how to do that more at the end.
Is Caffeine Bad For Bamboo?
So in the previous study, they mentioned coffee might have some kind of phytotoxic compound that could hurt your bamboo. Could it be caffeine?
Well after a little research the answer is not likely.
Two different studies found that low doses of caffeine actually stimulate plant growth (source, source). High doses of caffeine (over 11.2 kilograms per acre) inhibited both plant growth and weed growth.
Don’t expect to buy caffeine by the kilogram anytime soon though! If you could then yes, small amounts of caffeine in your bamboo pots or bamboo groves would actually get them to grow slightly faster.
Just to be clear, the studies above were for annual plants like corn, soybeans, and oats. The extra growth occurred during the initial growth of these plants.
Would the same thing work for older bamboo plants? Possibly but I wouldn’t count on it. Also, as discussed in the previous section, spent coffee grounds hurt more than they help.
While they could add a little caffeine to the soil which would help your bamboo. The other unknown phytotoxic chemicals in the grounds will hurt more than they will help.
Do Coffee Grounds Lower the pH of Soil?
No. Spent coffee grounds have been leached of the compounds that make them acidic (e.g. cholorgenic acids and other phyto compounds). Adding SCG to soil will not lower the pH of soil.
Instead, if you want to lower the pH to 6 (ideal for bamboo) then you’ll need to add 4-6 inches of peat moss and till it into the soil. That should last for 2 years.
You can also add elemental sulfur. Do this the year before as it will take time. Soil bacteria will break downt the sulfur creating sulfuric acid which reduces the soil pH. Aim for a soil pH of 6. (source).
|Sulfure needed to lower pH to 6 (ideal for Bamboo) [pounds per acre]|
|Current Soil pH||Sandy Soil||Loamy Soil||High Clay Soil|
Since you likely aren’t trying to reduce the pH in a giant grove of bamboo that’s several acres, we’ve recalculated the above into grams of elemental sulfur per gallon of potting soil.
|Sulfure needed to lower pH to 6 (ideal for Bamboo) [grams per gallon of potting soil]|
|Current Soil pH||Sandy Soil||Loamy Soil||High Clay Soil|
What Ph And Soil Conditions Do Bamboo Like Best?
Bamboo prefers a soil pH of 6.
Be careful when changing your soil pH though. It’s really easy to overdo it. They’ll you’ll be stuck only growing azaleas, blueberries, and other acid lovers. Or spending a ton on lime trying to raise the pH back up only to add a bunch of salt to the soil in the process.
Can You Use Coffee For Bamboo Pests and Weeds?
Yes, as discussed in the study above, spent coffee grounds mixed into the soil will reduce the growth of any plant at first included weeds. Coffee isn’t an herbicide though and will not kill weeds.
The study was not able to deduce which compound in the grounds actually hurt plants. Plus it only slowed the growth.
You’re better off tilling or removing weeds by hand and sending your used coffee into the compost bin.
Also, no, coffee grounds do not deter slugs or other pests. Caffeine itself when sprayed on plants will deter slugs and snails.
Spent coffee grounds do not have a lot of caffeine left. Informal gardener studies have shown that slugs don’t mind crawling over spent coffee grounds at all.
The most common pests you’ll find on bamboo (aphids, scales, mealybugs and mites) are best controlled using a real insecticide or via a diluted soap spray.
Just mix one tablespoon of soap per quart of water to make a quick anti-pest spray for your bamboo.
How To Use Coffee Grounds To Fertilize Bamboo
The best way to use coffee grounds to fertilize your bamboo is to compost them first then add them to your bamboo pots or your outdoor bamboo grove.
Worms love coffee grounds as they are easy for them to eat (small pieces). Coffee will break down in a vermicompost bin indoors in just a few weeks.
An outdoor compost bin if aerated can be used to break down coffee in a few weeks as well.
Hi, I’m John Stephens, chief editor and writer for Totalgardener.com. I’ve been gardening and raising animals for over 15 years starting with a small backyard plot in Northern Virginia where I grew corn, potatoes, squash, and using a high mulch technique called the Ruth Stout Method. I also raised ducks and small mammals for meat and eggs in a movable pen similar to the ones used by Joel Salatin. I later moved to Colorado where I experimented with growing greens using aquaponics inside. I eventually added a microgreens setup and home sprouting operation. I’m excited to share everything I’ve learned plus more from the other local gardening and animal raising experts I know.