Why is "Slow release fertilized soil" bad?

I’ve seen it recommended to stay away from slow release fertilized potting soil such as Miracle Gro.

I’m wondering what specifically is the reason? I started some seeds in some of this over the counter soil and did notice some nute burn but they seem to be overcoming that. I took two others and re-potted them in natural compost mixed in and they look great.

Just wondered what the science is, in regards to “staying away” from this type of soil and whether or not there is something I can do to counter any bad reactions from here on out.


Time released fertilizers of any type are too strong for cannabis. Plus people tend to start their own supplement program ignoring what’s already in their mix. Lastly, it’s usually found in peat based mixes that are highly acidic (low pH) and then pushes the pH let every time you water.
Add all that to the new moisture control technology and your have a mix that’s going to be too wet, too acidic and too highly fertilized.
Lastly, when it’s time to switch to a high PK ratio to initiate blooming, you will still have high nitrogen fertilizer being released in the pot. It’s just a recipe for disaster.


I tried to combat this by cutting the Miracle Gro with an equal amount of Ocean & Forest but the plants still suffered. Now I have six 1.5 cu ft bags of Miracle Gro that I will probably use as mulch under my mango trees.
Miracle Gro makes a decent product. It’s just wrong for cannabis.

Hmmm I was advised that it was just right for growing weed on this sight as a matter of fact?? Like I said earlier experimentation is the best teacher…

Well, I’m seeing the results of what Sir_Charles is describing. I had already put the seeds in peat pots to germinate using the pre-fertilized soil before I read Bergman’s advice against it.

I noticed it immediately. I did transplant two into a natural soil and they seem to be adjusting very well. The others are still in peat pots and are suffering.

I was just wondering the science of why and now I know. Thanks, as it sounds like a losing battle to try and work with it. It’s the first time I’ve done it this way and was fooled by the marketing on the bag.

Time to go back to basics and the way I always did it. It takes away too much valuable growing time to try and adjust your way out of it.


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I agree with @Sir_Charles_Kane that was well explained.
I always used that type of soil and it could have very well have been me @bulldog1 who spoke highly of the soil. ( Some one else mite hide ) from a statement like that. But not me
If I’m wrong i’ll admit it ! and after @latewood set me straight on the soil issue ( I am hard headed lol )
I changed to ProMix BX and now have much better results. So even us seasoned growers are still learning.

B Safe

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Never too old to learn! Especially in an era where info and technology are constantly changing. When I first started growing all that was recommended were fish fertilizer and some good dirt, ha. Guess what? It made pot. Good fundamentals are always key. With the Internet and Google information is always right with you. I love that.

I’m not one to throw names around but I was told that the Miracle Grow for seedlings and The Miracle Grow Moisture Control were 2 good products for growing. No big deal at all again it goes back to opinions and trial and error. Keep On Keeping On…

Thank you both and I am and will keep on keeing on…:grinning:



Believe it or not; I learn from you guys too.

One thing I want to say about advanced technology. There is no new better way to grow anything. No new science…really, and Nothing that has not been done or tried. you can dtill grow the highest grade of MJ wiith fish emulsion and worm castings…etc.

It is all about the grow; Not what you add to it. (As long as you have the necessary components to your medium and or nutrients.

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Yes …exactly what I have learned from both you and Stoner.
Thank you very much.


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Thanks for helping us! :smiley:

I’m new to the outdoors grow got some great seeds looking for the right soil mix to maxamiz my grow time any help on this would be great

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If you search the forum you’ll find tons of recipes for soil mixes and how to amend soil outdoors as well. Here’s just a quick link for you to a thread of one of the best growers I know


Hey thanks for the in put I have a very good strained of skunk I have access to any kind ferterliz their is I just need to figure out soil ( pounds) to nitrogen and maybe some potash?

I’m looking for the right mix of soil and nitrogen level got good strains of skunk would pot ash help mellow the harshness of high ph level

I use osmacote for years yes it can burn at first if you don’t have a healthy plant.Be aware when it says 3 months these ferts are tempature activated and in a warm room will only last about half the given measure of time,plants love it and grow like crazy. use whatever is easy to aquire you can grow great pot with just about any available ferts.