When to Start Using Fertilizers with CannabisIn this article we’re going to talk about when to start using fertilizers with cannabis. People always ask us when they should start using fertilizers on their plants, but honestly it depends on your grow method, the strain and the phase that the plant is in.

Depending on the phase your grow is in your plants are going to need certain nutrients in higher proportions; they need more Nitrogen in growth, and phosphorus and potassium for the flowering period. Cannabis plants absorb large quantities of these nutrients as well as others, so if they don’t get them through irrigation then they’ll probably end up showing deficiencies through stains on the leaves.

To start using nitrogen during the growth phase you’ll need to wait for your little plant to grow the roots out enough so that it becomes slightly stronger. It won’t need much more than some humidity to germinate and grow during the first few days, but once it begins growing aster then you’ll need to start using a growth fertilizer.

When to Start Using Fertilizers with CannabisYou should begin off with small dosages; if your product says 4ml/L for adult plants then you need to start off with 1ml/L, and only begin using it once the leaves on your plant have three points. Once those leaves appear you can start using your growth fertilizer in the irrigation water. Once the plant begins growing more then you should raise the dosage until you reach the maximum milliliters allowed, and always use it with every second watering.

For the rest of the grow, regardless of what products you use, you will need to use them on every second watering or else you’ll burn out the roots. If you notice the plant getting yellow then you can use fertilizers twice in a row, but if it gets a dense dark green color then you’ll need to lay off on the fertilizers for a couple of waterings.

Once the female flowers begin showing then you’ll need to begin using flowering fertilizers. Just like in the growth period, you’ll need to start off little by little until you reach the maximum milliliters stated by the fertilizer manufacturer, alternating between pure water and fertilizers.

When to Start Using Fertilizers with CannabisEach brand has a different range of products, so depending on the brand you go with you’ll need to use more or less products for both growth and flowering, although in this article we’re just talking about WHEN to use them.

If you buy a product with root stimulants in it then you should use it during the first two growth weeks and for two weeks after every time you transplant. If you have a flowering stimulant then you’ll need to use it once you flip the lights to 12 until the first flowers start appearing.

If your chosen range of liquids has a fattener with a high PK you’ll need to use it during the last phase of the flowering period, the fattening period.

Author: Javier Chinesta
Translation: Ciara Murphy

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Erik Collado

With more than 10 years of background in the cannabis sector, his experience and knowledge are the base of GB The Green Brand’s success

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34 replies on “When to Start Using Fertilizers with Cannabis”

I purchased 3 different fox farm fertilizer and had no clue which to use when. After reading your article I was able to make sense of the fertilizers. Thanks. Robert

We’re glad we could help, Robert! This article’s a bit on the older side, we’re updating our blog weekly with new posts so be sure to get back to us if you have any other queries!

Fox farm.. love big blooms for sure… Strawberry Gary from lice 52 Strand unfeminist

Need to know what fertilizer to use on my pot plant during the growing season in my garden. Also during the time when buds start to form.

Hey Richard!

There are an enormous amount of fertilizers designed for cannabis plants, but to keep it simple, you’ll need something that contains nitrogen, phosphorus and potassium. A fertilizer high in nitrogen is perfect for the growing season, and another high in phosphorus and potassium should do you for the flowering period. Check out some of our feeding schedules if you want to use a complete range of professional fertilizers for the best results.

Is it possible to grow my marijuana without using fertilizer? I’m using Dr. Q’s Filthy Rich (Organic) soil to grow it. Also, if I do have to use fertilizer, can I use miracle grow as a substitute considering how rich it is in nitrogen and minerals?

Hey Sammy, you don’t have to use fertilizer or nutrients as long as you’re using soil with plenty of nutrients. We haven’t tried that particular brand, but as long as it has a decent amount of nitrogen, potassium and phosphorus you’re good. If you’re going to use any sort of additive we recommend using base fertilizers for the growth and flowering periods too, as some additives can cause an increase in nutrient demand and your plant may not be able to keep up.

Long story short is that you can grow without adding any extra fertilizers or nutrients to your water as long as you’re using decent soil. I know of a few people that grow as organic as possible, simple soil and just water – you may get less yield but the plant will still grow. I hope that helped!

Hi I’m growing my first plat indoors what do I need to start off with and what brand product is best for cookie seeds.

Hey Raymond!

You can check out this post on everything you need to get started growing indoors.

There’s no brand that’s best for a particular type of seed or strain; it’s more of a learning and experience process until you find the right brand for you. We also have plenty of posts on different nutrient brands and their specific feeding schedules, make sure to check them out. We do recommend uding organic nutrients if you want to improve flavor and aroma, although mineral products can increase yield.

I have this espoma organic start, plant food and was wondering if and when I could use this on cannabis, and which stage I could use it in? IF SO!?!

Hey Raymond, we’ve never used that product but I did a bit of digging and it sounds okay for cannabis (if you’re growing in soil)! That particular product is specific for vegetative periods and root growth, so you’ll need to find an equivalent for when your plants are in bloom, as they require different amounts of nutrients for each phase. Keep in mind that if you’re going to use this product, everything else used should be organic (soil, other products etc.) or else you’re wasting all of that natural goodness, and you should try keep your products in the same brand.
I highly recommend getting yourself a small nutrient starter kit, we stock plenty of different brands on our webstore if you want to check them out – https://www.growbarato.net/en/126-fertilizer-packs?order=product.price.asc
Hope we could help!

So I have these tiny little (I guess) clay flower pots, I didn’t germinate my seeds as I was told I didn’t have to and that it would only take longer to see a sprout, also they said it was more risky to damage the root…..anyways like I said I didn’t germinate, and I have a bag of SCHMIDT water soluble plant food, do I use the plant food with my first watering?? or do I wait??? if so how much do I use?? I mean do I do like the package says, and fill the pot till the water starts to flow out of the bottom??

Hi Les,
If you haven’t germinated your seeds before putting them in your clay plugs, do NOT water. They must go into humid plugs – seeds and seedlings are much too frail to deal with that amount of water, it would rot them, and they also don’t need any nutrients until they have 2-3 pairs of leaves. I’m not sure who told you not to germinate them, but although it does take longer, it’s a much surer way of guaranteeing success, as this method is often prone to failure, especially if you don’t have much experience.

How soon should I start ferterlizing my plants in using a fish a thank emulsion I bought at home Depot and steer and chicken manuer is this good to use during growth and flowering

Hi Ismael,

Could you give me the exact name of the fish emulsion product?
Chicken manure contains high amounts of nitrogen, and lower amounts of phosphorus and potassium, meaning that it can be used both during growth and flowering, however we always recommend using growth and flowering-specific products for cannabis.
Your plants should start feeding normal amounts of nutrients once they’re a week or two old, depending on their size – you’ll need to increase their feeding schedule as they grow, and use bloom-appropriate products once it begins to flower.

I hope this could help, don’t hesitate to give us more details regarding your grow (indoors, outdoors, strain, product names and composition)

Yesterday I gave my autoflowers the first dose of bio grow, 0.5 ml / liter, but I think I made a mistake because they are only nine days old and the second set of leaves is just popping up, should I continue to give only water? Could I have damaged them?

You should continue to give them water until you can see the results from your feeding. If they seem okay, you can continue with the feeding. It’s all about reacting based on your plants’ reaction.
Kind regards,

How old do my bud plants have to be before I give them miracle gro all purpose plant food.my plants are 30 ‘days old

Hi Ricky!
It’s always best to measure when you can start feeding your plants by size rather than age; if your plant has 3 or 4 nodes, which is to say, 3 or 4 pairs of leaves, you can start using small doses of nutrients, which you’ll have to gradually increase.
Kind regards

I’ve just went into 12/12 lighting schedule, I water (1gal/plant) every 3rd day, fertilize once a week basically a 5:1 ratio with my vegetative mix and a flowering mix. Too early to tell if it’s enough or not enough fertilizer. Curious if I should lessen the mix and fertilize more frequently or continue on the same path?

Hey Steve!
Fertilizing once a week is the best bet; if you accidentally go overboard, they have plenty of time to absorb and get rid of any blockage by the next time you use nutes. I’d recommend keeping on the same path of fertilizing once a week, increasing your flowering mix progressively as the plant begins to show its flowers.
Kind regards

Is there any problem in changing the brand of nutrients being used….been using Mills A & B nutrient products…was considering switching over to a Humbolt Gold brand starter kit which also contains an A & B nutrient. Thanks

Hi Chuck!
You shouldn’t have any issues but we highly recommend checking the composition of both products and comparing them; if there are any drastic differences, we’d recommend holding off and using your new nutes for your next grow, in case you accidentally stress your plant out.
Kind regards,

i am growing early skunk and northern lights, both autoflowering, suppose to be 90 days from seed to harvest they are just starting to flower after 110 days, i used mostly compost with with some soil mixed with it and miracle grow 20 20 20, massive plants. i fimed them which i’m told i should not have done with autoflowering but it’s done now. my question is do i need to fertlize any more in the flowering stage or will the compost be enough? we have frost in another month and i am growing outdoors in 5 gal buckets, too big to move inside

Hi Milton
90 days is more of a guideline, the thing about autos is that they’re not entirely stable and can vary in flowering times.
During the flowering stage, cannabis plants need a bit more of certain nutrients to fill out their buds and not as much nitrogen as during the growth phase. If you can, switch to the Bloom version of miracle grow which is 10-52-10, much more adequate for plants during the bloom stage. Regarding the frost, if you can’t move them in try and see if you can put them somewhere with cover or place a tarp over them so that morning dew can’t settle.
I hope this helps!

Good Morning
Can I use miracle gro plant food spikes ? I’m 13 days in . All 3 of my babies have at least 12 leaves. I started growing in the miracle gro soil .


Yes, you can use it but do not put it really close to the roots.

Best regards.

Hi, first time pot grower.
I germinated, and planted them in cow manure in a small pot. Some leaves are turning yellow. I was wondering if I can use 20 20 20 fertilizer? I bought a ph meter and it said 7. Debating transplanting to an intermediate pot or the last big pot for them.
Is 20 20 20 ok as a fertilizer?


According to our team, 20N 20P 20K it’s too much, particularly for small plant, you will kill them.
Later when the plant will be taller, maybe the half of this.
But now they are too young for that.


I have some small cannabis in my garden probably 2 weeks old. Can I use any fertilizers to increase their growth or should I wait for them to mature and then apply any fertilizers?

Hello, 2 weeks are enough to start to use fertilizers in the plants.
Always consider the dosage indicated by the manufacturer of the product.

Hello, I have a seedling that was germinated u til it had a 1/2 inch tap root, then placed in a 6” pot with organic soil. It has only grown about .5 – .75 inches above the soil in 5 days. It has a small pair of flat round leaves and a larger pair of spikey leaves. All green. It’s in an enclosed controlled environment with led lights, humidifier and on a seedling mat. Should it have grown more by now or is it ok? No nukes added yet. 68dg with 64% humidity and 18/6 light schedule as well as an air filter 24/7. Thanks

Without pictures is noy easy to judge, but it seems that the problem is that it needs to be in a bigger pot to continue developing.

Kind regards.

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