Cannabis Science

Is Weed Ash Good for Plants?

ash black and white photo

If you’re a plant parent, you’re always looking at new ways to care for your plants. And if you’re also a stoner, you’re probably staring at a pile of weed ash right now when the thought crosses your mind: is weed ash good for plants? You’ve come to the right place! Before tossing it in the trash, here’s what we know.

Photo: Unsplash

Is Marijuana Ash Good For Plants?

It’s not uncommon for stoners to try and use up every bit of weed. Stoners have found a use for weed stems, bong water, and seeded weed. 

There is no shortage of creativity in the stoner community!

But what about marijuana ash?

There is not a lot of research on whether marijuana ash is suitable for plants or not. 

However, weed ash can be good for plants according to cannabis experts. Winston Peki, cannabis expert and founder of Herbonaut, told us, “Small amounts of pure marijuana ash can be beneficial in some cases for some plants. This is because pure marijuana ash can contain some nutrients, especially potassium.”

But before you go throwing all of your marijuana ash on your plants, there are some things you need to be aware of. 

Peki says, “The key points here are ‘pure’, ‘in small amounts’, and ‘some cases’. If there’s any tobacco ash mixed with the marijuana ash, it’s already potentially toxic.”

In addition to that, Peki says, weed will increase the pH of the soil (if the soil is about pH 6-7). Therefore, depending on the needs of the soil this could be an awesome addition or a disaster. However, if you only add a small amount the pH won’t be affected too much. 

Therefore, if you want to add weed ash to your plant, bear these things in mind. 

Can You Add Marijuana Ash to Your Compost Heap?

Well, stoners have been adding marijuana ash to their soil and compost heap.

A Reddit user said, “I add mine [marijuana ash] and have never had a problem. Though the amount of ash I add is minuscule compared to the size of the pile. I also dump my bong water on my pile when I switch it out. Waste not, want not lol.”

Another said, “Yeah it’s burnt carbon. I don’t know why you wouldn’t be able to put any ashes besides carcinogenic in a compost pile.”

Peki agrees that you can add weed ash as well as other parts of weed to your compost heap. He told us, “things like leaves and stems from previous grows can definitely be used in compost. Just make sure they are only a part of everything you add and not the only major thing. Cannabis leaves don’t have an ideal carbon to nitrogen ratio, but when you combine them with stems, the ratio will be closer to the ideal of 30:1 (Carbon:Nitrogen).”

Is Ash Good for Plants? 

There is more research on using other types of ash, namely wood ash in gardening. The Royal Horticultural Society says, “Ash from wood fires, such as bonfires or wood burning stoves, can be a useful additive to the compost heap or can be applied directly to fallow ground and dug in. It can be a natural source of potassium and trace elements.”

Of course, you shouldn’t just add ash to your flower bed for no reason. Wood ash, for example, is used to remedy really acidic soil. Therefore before you add it, you may want to do a pH test. You should also check the pH levels after you add the wood ash because you don’t want your soil to be alkaline. That will present a different set of problems. 

As a matter of fact, it’s good practice to figure out exactly what your plants and soil may need before adding anything to them. 

At the same time, not all ash is worth the trouble. The Royal Horticultural Society, “Ash from coal or anthracite is best disposed of through the council rubbish collection since it has little or no nutritional benefit and is potentially harmful to soil, plants and consumers of edible produce.”

What Else Can I Do With Ash?

Besides your compost heap and soil, there are other things you can do with ash. This Old House says you can wood ash to:

  • Keep bugs at bay
  • Make homemade soap
  • Clean

Unfortunately, we’re not sure if marijuana ash serves the same purpose. 


Is weed ash good for plants? It can be! However, it depends. Marijuana ash can add certain essential nutrients to your soil such as carbon and nitrogen. When adding weed ash to your soil, make sure that you use only small amounts of pure marijuana ash. Therefore toss any ash you have with tobacco remnants in it. Finally, remember that marijuana ash can increase the pH of the soil. That’s great if your soil is a bit too acidic. However, if your soil was already too basic then you could have a problem if you added tons of weed ash. If you have other types of ash, you may be able to add them to your plants too. 


About Trevann

Trevann is Stoner Rotation’s Jamaica-based lead writer for the Science section of our cannabis blog. She graduated with honors receiving her Bachelor of Science degree in Molecular Biology from the University of West Indies, Mona. For the last three years, she has covered some of the biggest questions around cannabis and health underpinned with research from supporting studies, medical journals and scholarly articles. Got something on your mind? You can reach her at [email protected].