Grow Mediums Re-using organic soils and heavy metals

[CannadaJ]

I started growing cannabis about a year ago. I made a decision to grow using organics (Gaia Green) and to re-use my soil. I till and re-mix my soil after each grow but mostly wanted to do this for sustainable reasons related to peat moss harvesting (and also the impacts of coco coir that are often not talked about).

I've been reading a lot about heavy metals, and want to get a better understanding on how to reduce the risks when re-using soils and using dry amendments. So far, it seems that a few dry amendments can introduce heavy metals in soils (kelp meal, rock minerals, poor quality composts and earth worm castings, etc.). There are also products and practices that can reduce the plant uptake of heavy metals such as;

1. Silica
2. Humic/Fulvic acids
3. Rich biodiversity
4. Proper Ph levels
5. Bio accumulator cover crops

That being said, wouldn't re-using soil lead to a greater accumulation of heavy metals over time? If we're using amendments and practices that prevent the plant from absorbing them, they are essentially increasing in our soil each grow.

Would love to hear how some of you are approaching this issue when re-using soils and dry amendments.

Cheers,

J

 

[JP1]

I started growing cannabis about a year ago. I made a decision to grow using organics (Gaia Green) and to re-use my soil. I till and re-mix my soil after each grow but mostly wanted to do this for sustainable reasons related to peat moss harvesting (and also the impacts of coco coir that are often not talked about).

I've been reading a lot about heavy metals, and want to get a better understanding on how to reduce the risks when re-using soils and using dry amendments. So far, it seems that a few dry amendments can introduce heavy metals in soils (kelp meal, rock minerals, poor quality composts and earth worm castings, etc.). There are also products and practices that can reduce the plant uptake of heavy metals such as;

1. Silica
2. Humic/Fulvic acids
3. Rich biodiversity
4. Proper Ph levels
5. Bio accumulator cover crops

That being said, wouldn't re-using soil lead to a greater accumulation of heavy metals over time? If we're using amendments and practices that prevent the plant from absorbing them, they are essentially increasing in our soil each grow.

Would love to hear how some of you are approaching this issue when re-using soils and dry amendments.

Cheers,

J

You can have your soil tested. Also kis organics nutrient packs are treated for metals and they'll also decipher your test results for you. Plus @KIS is a member on here and full of great info for organic growing

 

[eprotege]

Cannabis is a bioaccumulator. I know that in Canada, some First Nations are using Cannabis to remove heavy metals from contaminated soil. I assume they aren't consuming it afterwards. If you are composting the whole plant into the soil after each grow, then yes, I can see an accumulation of metals. Conversely, if the plant composted into soil used elsewhere, then the accumulation isn't necessarily consumed in the flower. In that scenario, the plant pulls the metals out of the soil and you are removing the plant material.

I'm interested in what others have to say on this as I'm just a noob.

 

[Hog_M@Gundy]

Heavy Metal Testing Best Practices Living Soil Growers

Heavy Metal Testing and Best Practices for Organic Living Soil Growers We must stick together as a community and handle these problems out in the open for the betterment of all those that are going to grow in living soil and don’t want to be forced into hydro for fear of heavy metals. When we do...

buildasoil.com

 

[CannadaJ]

Thanks. I do not compost my cutoff leaves so that could help. I'm interested in a "avoid heavy metals 101" for organic growers since I'm thinking of mixing a new soil with this in mind. The Build a Soil article was good differentiating between organic and inorganic arsenic.

It does seem, however, that my use of Kelp should stop if I intend to reuse soil.

J

 

[Mañ'O'Green]

@CannadaJ based on the above article I think is has more to do with the content of your inputs and I would look at the arsenic content of the water you are using. As long as you are using nutrients and composts with known low levels of arsenic I don't think you would ever run into trouble. You could also do a soil rotation with a Chinese Ladder Brake Fern.

I do strict crop rotation in my vegetable gardens for so many reasons.

 

[CannadaJ]

Has anyone using Kelp and re-using their soil (no till or other) had their flower tested? Would love to know how much of a problem it is, if at all.

 

[KIS]

I started growing cannabis about a year ago. I made a decision to grow using organics (Gaia Green) and to re-use my soil. I till and re-mix my soil after each grow but mostly wanted to do this for sustainable reasons related to peat moss harvesting (and also the impacts of coco coir that are often not talked about).

I've been reading a lot about heavy metals, and want to get a better understanding on how to reduce the risks when re-using soils and using dry amendments. So far, it seems that a few dry amendments can introduce heavy metals in soils (kelp meal, rock minerals, poor quality composts and earth worm castings, etc.). There are also products and practices that can reduce the plant uptake of heavy metals such as;

1. Silica
2. Humic/Fulvic acids
3. Rich biodiversity
4. Proper Ph levels
5. Bio accumulator cover crops

That being said, wouldn't re-using soil lead to a greater accumulation of heavy metals over time? If we're using amendments and practices that prevent the plant from absorbing them, they are essentially increasing in our soil each grow.

Would love to hear how some of you are approaching this issue when re-using soils and dry amendments.

Cheers,

J

It's all about soil management. You can reduce heavy metal inputs and lower levels in the soil. Some keys to this are to remove roots, run a higher pH, use a high quality biochar, limit mulches, check your water and make sure it is truly clean, and then know what you're adding every cycle based on your inputs. We are successfully managing heavy metals in many states using this approach. It's a complicated issue and requires you to look at your SOPs and everything that comes in contact with your plants, all the way down to the dust from outside. It is possible though. If you're not being tested by a regulatory body, then the simple changes are just to reduce inputs high in heavy metals.

 

[CannadaJ]

It's all about soil management. You can reduce heavy metal inputs and lower levels in the soil. Some keys to this are to remove roots, run a higher pH, use a high quality biochar, limit mulches, check your water and make sure it is truly clean, and then know what you're adding every cycle based on your inputs. We are successfully managing heavy metals in many states using this approach. It's a complicated issue and requires you to look at your SOPs and everything that comes in contact with your plants, all the way down to the dust from outside. It is possible though. If you're not being tested by a regulatory body, then the simple changes are just to reduce inputs high in heavy metals.

Thanks KIS.

My tap water if very clean and usually use that and once in a while some distilled water. Although I believe that the Gaia Green is from quality sources, I think reducing the amount of Kelp is something I'll likely do moving forward.

That being said, it seems to me that most of the heavy metals would go in the vegetative structures of the plant (not just the flowers), and defoliation would certainly help remove some heavy metals by discarding the leaves. I also remove my roots, and use a high quality biochar along with a few amendments known to help reduce absorption (silica).

Mostly starting to wonder if re-using soil over 5 or 6 times might not be the best idea purely in terms of heavy metal concerns.

 

[KIS]

Thanks KIS.

My tap water if very clean and usually use that and once in a while some distilled water. Although I believe that the Gaia Green is from quality sources, I think reducing the amount of Kelp is something I'll likely do moving forward.

That being said, it seems to me that most of the heavy metals would go in the vegetative structures of the plant (not just the flowers), and defoliation would certainly help remove some heavy metals by discarding the leaves. I also remove my roots, and use a high quality biochar along with a few amendments known to help reduce absorption (silica).

Mostly starting to wonder if re-using soil over 5 or 6 times might not be the best idea purely in terms of heavy metal concerns.

Re-using the soil allows you to lower heavy metals if you're able to manage your inputs and know what's in them. You are correct that most heavy metals accumulate more in stem and root and leaf matter than in the buds. This is useful to know when submitting samples for testing and also when re-amending your beds by removing as much root mass as possible.

Keep in mind that 'clean' water is all relative. 1.3 ppb of arsenic in your water for example (which is totally a safe level for drinking), will add way more heavy metals to your soil than adding some soft rock phosphate or kelp meal, which is closer to 10-30 ppm of As.