This is a big one...How much Miracle Grow blue powder mix per gallon


The most common miracle gro fertilizer in question(THERE ARE OTHERS) ALL PURPOSE PLANT FOOD NPK OF 24 8 16----------Okay, I consider this a big big question from those who have finally and ultimately figured it out, I would like to continue using miracle grow all purpose fertilizer, while I am a beginner to save my valuable and good booster and such I bought, and not waste the stuff while I have been “learning” through the school of hard knocks mistakes, later when I have successful clones, knowledge, I am going totally organic, probably four or more months from now or who knows. So on a couple plants I want to use miracle grow, maybe all of them instead of using slow release fertilizer soil I just bought, but use miracle grow like I do outside on other plants. The problem is there are stories all over the internet, the instructions are bad, mainly cause folks generally use a hose with a dispenser where you put the blue powder in a quart cup and water flows over it into a spray.
Now, the “one gallon quandary”, the bogus instructions for “one gallon” is use large end of plastic spoon which is 1.5 tablespoons per gallon and a half for outside plants. Or use small end which is 1/2 teaspoon for “indoor plants”. I think maybe plants in three or five gallon buckets are beyond “indoor plants”, to get a full effect of NPK of 24 8 16. I was using 1/2 teaspoon, and I think I was under nuting them in the five gallon containers, apart from other problems.

If a person does a search on the internet, there are opinions all over the place, I believe lots of bad stories from over nuting/too much powder or such. Now I know there must be a formula for how much soil, I’d think maybe two teaspoons per gallon of water is fine. I may already have damaged plants, I gave a tablespoon for gallon of water, my tap water, the fertilizer fixed the ph balance perfectly, and distilling water is getting tedious. Then I worried, so I poured another large quantity of water on all the plants, to thin out the mixture in the soil.

I swear I think when I am growing mainly in my shed later, I am gonna be so organic, the rooms will stink of either composted organic matter, and manure compost(maybe the sterilized steer manure my mother told me about(hey, what are elderly mothers with a lifetime of gardening experience for but to advise their 47 year old son how to maybe grow better pot!).

Anyway, calling out all those successful users of miracle grow blue powder or similar, its beginning to be an internet legend, I have read posts where one person says one tablespoon per gallon, then right after someone says one teaspoon per gallon, and then two more people with the same alternating opinion. If I had about thirty plants, I’d just find out with by figuring with a sampling which kills and which doesn’t. But wow, word to the wise, and I was not that day, never, never, after a successful first week, water clones again that are still wet, with a weak solution of miracle grow and water, …boom, heavily damaged and wilting, along with plants were drowned in excess water, I read that new clones, you can forget about fertilizing for a good long time, ah, doy ralph, I wasn’t feeling well that evening.

(of course, there are many users who are religiously against miracle grow, they either had bad experience, they have lots of “experience” now, or the all purpose aint good for complete veg/flowering cycle no doubt, but there are other ratio miracle grow they sell. Plus the fact that a chemical fertilizer needs to be stopped from use at least two weeks before harvest or it will affect cured taste quality).


Sorry. I did nbot read your entire post. If you want to know how to use Miracle grow; I suggest you read the directions; On the bag. Peace :slight_smile:


I’ve seen when using Miricle-Gro on marijuana that a lot of peeps seem to be using 1/2 of the measuring spoon that comes with the a gallon of water,then use it for a regular watering schedule.I would step that up to a full spoon once the plant gets larger.


Russ1, you must mean the 1/2 teaspoon end of that that plastic spoon. Problem is the instructions call to use the small 1/2 tsp for “house plants”, which I consider like prayer plats and other small potted decorative plants. Then the other end is for “outdoor plants” at 1.5 tbs per 1.5 gallon of water. That is the instructions given on the side, and I was unsure, but I swear that 1/2 tsp meant for “house plants” was giving a nitrogen deficiency, meaning not enough fertilizer to my plants.

I’m just looking for who has had success, and what were the measurements that worked for “you”. Anyway, the instructions given are not precise enough, and I don’t believe three to five gallon container weed plant are totally “indoor houseplant”, as I don’t believe .5 tsp per gallon of water is strong enough. Dunno.


No I meant the big end of the spoon.You’re only using it for regular watering schedule,and a gallon goes a long way.So don’t worry about overnuting the plants


WEll, ironically, I may have over nuted my plants, though, I had experimented with letting the plants get as dry as I could get them before I watered/nuted, and already had noted the weaker leaves going bad here and there, and I may have went to far on that and already damaged some leaves. Yeah, I think, step two would indeed using the large end, but half of it as you may be doing. I almost feel like going out on my porch right now, well, maybe my back porch for privacy, and replanting all the plants right now in pre fertilized soil.

Ya know, I’ve always been good with composted fertilizers, like an expert, I mean, lots and lots of experience, but “chemical fertilizers”, it has always been so easy to over do it, very easy, the only times it works out is with a garden hose hooked up with a reservoir sprayer. Then there is my water, a well water that has excess iron, maybe sometimes, a ph of 4, I used it for the first time the other day, the fertilizer brought the ph to the proper level of 6.

But they don’t look too bad, the most frequently previously damaged plants look the worste, but they are weak anyway, I’ve been reading a Jorge Cervantes encyclopedia, and planning my next moves, probably downsizing to three gallon pots down from five gallon pots. Somehow or another, I feel marijuana plants for the small time medical marijuana card grower are indeed the ideal, especially for watering control, meaning not staying wetter, longer. And I don’t trust the soil mix I did for them about three weeks ago.


I ended up just repotting all my plants, seven of them, to three gallon pots and with low nutrient slow release fertilizer pre mixed of 13 04 13 NPK. Not that I don’t still want to use Miracle grow as a cheap and effect grow fertilizer, and every so often something added with it.

I believe my soil medium in five gallon pots was improperly mixed up with too much of something, besides finding clumps of additions I made of dolomite lime and then some clumps of Epsom salts…

That large end of the “spoon”, Russ1, that is 1.5 tablespoons, I mean, I hope you are right about that measurement not wiping out marijuana plants. I’d have run some experiments myself, but as of tonight, I have about ten viable clones, maybe two or three more I reset. I have to do more clones, this time mistake free, so I can do “experimentations”, fertilizers, my ideas on composting, etc.

But really, this miracle grow fertilizer is important to me, I’ve read that miracle grow lacks “magnesium”, and raises the ph of the water, which can cause phosphorus and iron definciencies, needing chelated iron to be added. I don’t remember what chelated iron is. Of course, for myself, I have low ph well water, and adding miracle grow raises ph to 6 to 6.5 ph, just ideal for me, no wonder my outdoor frutis and vegetable plants have thrived with miracle grow and the water.

till the pre mixed slow release fertilizer wears off, I’ll probably use what I consider a weak mixture of miracle grow, the 1/2 teaspoon measure. Frankly, I want to get one of them test kits that test the water or soil for what nutrients and what level are present, I used something like this a few years ago helping my mother figure out why her rose bushes were dying off(the new place had a lot of sand, and it had salt and alkalynities above average come to find out)a seemingly foolproof way of “knowing”, anything and everything, and once I know, I can repeat what works.


Bud for indoor and small plants(seedlings to 12") I use 2 of the little spoons per gal.water. For outdoor plants over 12 " I use 1 large spoon per gal. More can be used if indoor grow are medium to tall strains.
When I used just one small spoon on indoor grow it wasn’t enough,and tried 2 and got great results.


NPK 24 8 16 is way too high in Nitrogen, in my opinion, and I would only use Miracle Gro for tomatoes, if I was going to use a miracle gro product for cannabis, and yes, as Latewood said, I’d follow the recommendations on the package and do a good flush the last week of flowering, at least.


I just had a big scare using MG on my flowering plants. It was marked especially for flowering plants and veggies. I used it at half strength and my WW ended up with Nitrogen Toxicity ! I am switching to Bloom (0-10-0) and adding NO nitrogen for the rest of the grow. I hate to damage a plant in Flowering as it may not recover fast enough to be as good as it could have been. I have pics of mine under “Flowering Problems?”

This is just my experience, take from it what you want. That is the cool part if this support site, you get a lot of opinions to consider.

Good luck and good buds to you! Keep on posting and let us know how it works, we all learn from you. Maybe some pics if you can. It helps everyone and it is nice to show off your work!



Forget about it M.G get What Roberto" recommends!


I used the MG tomato fertilizer during the veg stage. Just used it as the directions on the box indicated. For the flowering stage, I used the MG Bloom fertilizer. My outdoor potted plants were really healthy. Something I also did was put those tomato wire thingys around my seedlings just in case they needed support as they grew. I also used my hair (really long) and tied it around the wire thingys to keep the rodents away. You can also use your dogs hair too. I tied green ribbons that would blend in with the surroundings on them as well. I didn’t have any problems with pests last year.


I’m not familiar with the miracle grow tomato fertilizer, what I have been using is a “all purpose” mg, unless what you are saying is that all purpose is technically used for tomatoes?


Bud … the MG I use for veg is called MG Tomato Plant Food with a 18-18-21.

The MG for the flowering stage is called MG Flower Food Bloom Booster with a 15-30-15.

Last year was my first year growing outdoors … so maybe I’m using the wrong stuff. My 3 plants were on the small size, but I thought that might be because I didn’t plant the seeds until the first week in July and I used 5 gallon pots. I harvested the first week of October. I did yield enough for one daily smoker and another guy for six months.

Hopefully, if I’m using the wrong fertilizers someone will let me know.


Who knows if the “18” was wrong, someone already stated that “24” for nitrogen was too much, so maybe you are “right on”. Seems like I compared the “booster” sold on this site that I bought three sets of, and I thought it compared real close in npk to the miracle grow all purpose, but he says miracle grow for tomatoes is probably the best, I probably should order some up, its sort of limited around here in my neck of the woods, except I do have a Walmart supercenter, unsure if they carry tomato miracle grow.

I’ll be glad when I get my first indoor grow under my belt, and hopefully not have killed my seed started plants,…by over-nuting, over-watering, or “over” everything else. I too wished I could grow a few plants outdoors, just a few plants mind you, with my license of okeeedokeee for medical, but there are so many things attacking my garden the last couple years, …moles, white powder mold I need to spray on kiwis right now, bugs, snails, you name it. Then, I live in an area near the Oregon coast that the coast guard flies right over, I mean, like real close cause they monitor the dunes national recreation area, so close I thought they were checking someone out for whatever one day, and even though I am “legal”, I worry about hassles, apart from neighbors, etc etc. Actually, in Oregon, if the coast guard saw like four plants growing outside, by july 1, ha, oh well, its legal recreational then, but then there would be the “thieves” etc. I wished I had a greenhouse, nothing fancy, that could be lockable but unable to see inside what is inside, maybe a plexi glass roof, all my neighbors know I try to grow strawberries, raspberries, tame blackberries, rubarb, even did tomatoes year after year till I can’t hardly look at tomatoes anymore, and many other things, but really, I can forget about growing outside, where I am at, of cannabis.


So far, well, I am awaiting on a “clone king” aeroponic 36 station cloner, my plants, most of them, are very bushy, the five oldest, requiring watering more frequently, now every two or three days with miracle grow added in, likely the smaller amount added every watering is good instead of one weekly larger feeding(maybe), but it corrects the ph in the water, though I have a ph adjuster solution up or down, and the plants are using a lot of nutrients due to them being untrimmed yet. I have been using miracle grow blue powder, first I used 1/2 tsp and didn’t note any damage, other than a likely nutrient deficiency with yellowing of end of leaf, so now I am at 3/4 tsp, and maybe I might go to two 1/2 tsp(small end of measuring spoon) to make 1 tsp, still figuring it out. The plants are large-ish for the space they are in, and have a lot of branches I am waiting to snip, plus one or two of the plants are still recovering from previous damage. I now have repaired my diesel truck by clearing out of the fuel lines gelled fuel(from biofuels that coagulate in winter where I am at, if I don’t drive it all the time), and now I can go buy some two by four wood to frame me a my legal personal grow rooms in my shed.
After I know what I am doing, am set, I will use the grow booster sets I have, from this site, on my recovered plants, errrrr, if the heavily damaged ones are still “female” to be verified with small clones. If I do my reading, don’t redamage my plants heavily with mg powder, and they are still female, and I use properly the three piece grow set, my plants will be flowering when they are over four months old, maybe as a flunkie I’ll get a lot of ounces for my health issues, diligently reading these pages, my books, and being careful from now on.

Like I said previous, I’ll likely get away from using miracle grow powder, going with the organic nutrients, and even composts, for “quality”.


It is not a deficiency(not enough), not likely, it was a toxicity or over dose.

The blue powder means nothing to me. I don’t know what that means other than some are different colors and I believe the miracle gro for tomatoes is red.

The miracle gro powder for tomatoes is the only one that even comes close to having a well balanced nutrient proportions close to what cannabis needs. The problem with halving the strength means that all other nutrients besides nitrogen are also less, and cannabis needs lots of potassium and phosphorous. Miracle Gro in and of itself is not really the problem and not necessarily bad for cannabis if used correctly.

Also pH is a huge factor, pH can cause certain nutrient to become more available or less available, this in itself can cause a nutrient toxicity or deficiency.

Think about this, MG for tomatoes is 18-18-21 and more close to the ideal ratio for cannabis at full strength, and you are using 24-8-16, so at half strength, you only have 12-4-8, and at a 1/4 strength you are at 6-2-4. You don’t have anywhere near the right amount of phosphorous or potassium.

I’ve seen cannabis grown healthy and with thick oozing buds, grown the entire lifespan on something with as little as 4 or 5 in the nitrogen range and as high as 15 or even 18 for the phosphorous and potassium, and so an NPK of something like 5-15-14, and as you can see, your nutrient proportion just can not supply those nutrients at the right ratios no matter what you do.


Yeah, and of course, I have the plants in the pre fertilized soil of 13 04 13 turf king brand. Seems when I use the miracle grow, say, 1/2 teaspoon small end for “house plants” as described for the “all purpose plant food” by miracle grow, the leaves gained more green color, from where the top most leaves on the most previous damaged plants started turning yellow on the ends, lots of reddish purple stemming of leaves and leaf stems.
I was originally gonna just use very little of any fertilizer or hopefully none at all for weeks or a month, but the plants started looking damaged, is when I started with the miracle grow thing. I should have used just regular potting soil with no fertilizer.

Yeah, I’ve been concerned about the lower numbers for phosphorus and potassium. I think I might hang up the use of miracle grow, and start using the grow booster, but then there is that soil I used with pre fertilizer, of which I was almost sure that it wasn’t doing anything in a fertilizing way, from what I was seeing, or not enough. I do know that if I don’t kill all my plants before my aeroponic cloner comes, the next generations will be in non pre fertilized soils, unless I go composting real serious.

I’m quite possibly or most obviously giving too much nitrogen, which is why the weak plants show some yellowing in places.

**$Ya know, I really don’t think I know what the optimum npk for vegging is, unless it is the npk rating on the grow booster I received from here, it says 20 5 4 of npk for vegging, and that doesn’t seem a lot of P and K. I thought the “mass booster” of 2 4 15 was for flowering stage. I have me one of them test sets for testing npk, when one knows the optimum range, then they can add up what is used as a “fertilizer” and add up the numbers what is expected in the soil if pre fertilized. Though the soil that was prefertilized is like about a month of use now, sooner or later that pre fertilizer mix will have been used up, I’m stupid for using it, I am sort of thinking.

I’m gonna use the test kit on a half teaspoon of blue miracle grow mixed in a gallon of water to figure out npk of it mixed per gallon. I’ve been thinking about the likely lower levels other than nitrogen, especially phosphorus, a local store sells a phosphorus only mix, but I think it was supposed to be mixed with the soil upon potting.

I mean, I have a small book collection and download collection of growing cannabis, but I for the life of me can’t find the “optimum” npk ratings for vegging and flowering, in print.


I agree, I have been trying to figure that out also. One reference says to use NO nitrogen during the flowering stage and another says use 15-30-15. Was using 0-0-22 and 0-15-0 together to get a usable flowering mix but it did not seem to work after I used the 15-30-15 even after two flushes. I got some wicked Nute Burn from the 15-30-15… Not sure where to go right now. I’m going to try to max soil nutrients and only add flowering nutes this time. Still searching for the “Gold Standard” for flowering. Maybe Mr Latewood could drop in a thought on this. Thanks.

Good growing and Good Buds to all.


Last year I used MG for Tomatoes the one with the 18-18-21 for the veg stage. And they seemed to be okay. I was using garden soil in the pots. I used MG Flower Food Bloom Booster during the flowering period, which is 15-30-15. The plants did well and I had a pretty good yield out of 3 plants grown outdoors.

I blew it this year though … just realized I used MG Potting Mix with some kind of long-lasting fertilizer in it. I need to check the ratio on the bag … 21-11-16. I used seedling potting soil in the center of the pots to start the seeds.

Since the potting mix has fertilizer already in it … should I forego the MG for Tomatoes during the veg period?

BTW - Bud … the blue MG mix is for blooms and the red MG mix is for tomatoes.