Best fertilizer for cannabis plants 2025 – Our grow guide

Cannabis plants have high nutrient requirements – the right fertilizer determines the health and yield of your cannabis plants. But which fertilizer is best for cannabis ?

Why fertilizer is so important for cannabis

Cannabis is a heavy feeder – without sufficient nutrients , growth and flowering fall far short of their potential. In nature, hemp plants quickly extract nitrogen (N) , phosphorus (P) , potassium (K) , and trace elements such as magnesium and iron from the soil. A good hemp fertilizer balances these needs and prevents deficiency symptoms (e.g., yellow leaves due to nitrogen deficiency). Especially when growing indoors in limited soil, additional cannabis nutrients are essential for strong growth and abundant flowering.

Outdoor grows in natural soil also benefit from fertilizer: It improves soil quality and continuously supplies new nutrients. Cannabis plants can survive without fertilizer, but for truly fat buds and high potency, you need to feed them. In short: fertilizer boosts your plants and lays the foundation for healthy roots, lush foliage, and ultimately, heavy, resinous flowers .

Which fertilizer is best for cannabis?

Many growers ask themselves: " Which fertilizer should I use for cannabis plants ?" or " What is the best fertilizer for cannabis plants? " The truth is: There is no single "best" cannabis fertilizer – it depends on your conditions and preferences. Fundamentally, the best cannabis fertilizer should be optimally tailored to the plant's needs. During the vegetative phase, cannabis primarily needs more nitrogen for leaf and stem growth, while during the flowering phase, more phosphorus and potassium are needed for flower formation.

Quality and composition are also important: A good fertilizer – whether organic or mineral – contains all the major nutrients (NPK) and micronutrients that cannabis needs to thrive. Specialized cannabis fertilizers have an advantage here, as they are formulated specifically for hemp. In addition to the nutrient ratio, other factors play a role: for example, the soil/growing medium (soil, coco, hydroponic) and your level of experience. Below, we'll discuss which fertilizer is suitable for which plant. But first, let's get specific: Our top recommendations for the best grow and bloom fertilizers for 2025 for indoor and outdoor use!

Top Recommendations – The best fertilizers for indoor & outdoor growing

Granny's 2-Phase Grow & Bloom Formula: Perfectly tailored to the growth and bloom phases (Phases 1 and 2).

Below, we present the best cannabis fertilizers of 2025 – suitable for both indoor and outdoor hemp cultivation . From organic fertilizers to practical grow kits to proven brand-name products, we've got it all. Each fertilizer is briefly described, including its benefits, areas of use, and special features, so you can find the honest recommendation that's right for your grow.

Granny's Weed Grow Fertilizer (Growth Fertilizer)

This is our proprietary organic growth fertilizer for the vegetative phase. Granny's Weed Grow Fertilizer is 100% organic and was developed in collaboration with HESI, a leading manufacturer of cannabis nutrients. The NPK ratio of 4-1-4 is optimally tailored to the needs of the growth phase, with an extra-high nitrogen content for vigorous green growth. Its liquid form makes it easy to mix with irrigation water (dosage: approx. 7 ml/L) and won't clog irrigation systems.

Benefits: Promotes strong root and leaf growth, improves soil biology, and is suitable for all growing methods (indoor, outdoor, and hydroponic). It's also purely organic —without chemical additives—so it tolerates overfertilization and leaves no harmful residues. Application tip: Only plant in pre-fertilized soil approximately three weeks after repotting, as young plants initially find sufficient nutrients in the substrate.

Granny's Weed Bloom Fertilizer

Granny's Weed's Bloom fertilizer is the counterpart for the flowering phase . Also an organic liquid fertilizer, it provides an NPK ratio of 3-4-4 – extra phosphorus and potassium for lush flowering. It also contains magnesium and other trace elements to maximize resin production and flower density. Application is simple: approximately 7 ml per liter of water, about 2–3 times per week during flowering.

Benefits: Ensures larger, denser buds and improved flavor, as no synthetic nutrients are used. Ideal for environmentally conscious growers who prefer organic farming. Note: About two weeks before harvest, you should stop fertilizing to allow the plants to break down excess nutrients. This prevents fertilizer residue in the flowers (keyword: flushing ) and leads to a cleaner end product.

Granny's Weed Grow & Bloom Set (2-Phase Complete Set)

For those who want to cover both phases at once, there's the Granny's Weed Grow & Bloom Set . This contains one bottle each of Grow (500 ml) and Bloom (500 ml) fertilizer – perfectly matched as an all-in-one solution from cultivation to harvest. Each bottle (at 7 ml/L) is sufficient for approximately 70 liters of irrigation water, which is sufficient for several plants and grow cycles. This provides you with the complete nutrient program: During the growth phase, Phase 1 (Grow) supplies the plant with nitrogen for strong roots and shoots, and Phase 2 (Bloom) provides phosphorus, potassium, and magnesium for flower development.

Advantages: Simplicity – you always have the right fertilizer on hand without having to think too much. Both fertilizers are organic , improve soil fertility, and are also suitable for other demanding plants (e.g., tomatoes, chilies). The set is ideal for beginners who want to get started right away, but also for professionals who value a reliable basic supply. Tip: Follow the enclosed instructions – e.g., only add Bloom when the first flowers appear, and never mix the two fertilizers together (fertilize each phase separately).

Green Home Hemp & Cannabis Fertilizer Set (Grow & Bloom, 1L)

This * fertilizer set from Green Home is designed for both indoor and outdoor growers. The set contains two large 1-liter bottles: a growth fertilizer and a bloom fertilizer . The integrated pump dispenser makes it easy to measure the nutrient solution. According to the manufacturer, one set is sufficient for approximately 290 liters of water, enough to supply up to 72 plants (depending on the pot size). This will last you an entire season.

The Grow part, with its balanced NPK content, promotes strong roots and leaves, while the Bloom part , enriched with extra potassium and trace elements, ensures dense, resin-rich flowers. Both components consist of natural, organic nutrients and are versatile (soil, coco, hydroponic). Advantages: Easy application via pump bottle, targeted nutrition at every stage, and, according to the supplier, discreet shipping in neutral packaging – attractive for online buyers. The price-performance ratio (around €16 for 2 L) is also very attractive for the quantity.

Biobizz Try-Pack Indoor (Bio-Grow, Bio-Bloom, Top-Max Set)

The * Biobizz Try-Pack Indoor Box is a popular classic, especially among organic growers. This set contains three 250 ml organic fertilizers: Bio-Grow (growth fertilizer), Bio-Bloom (bloom fertilizer), and Top-Max (bloom booster). Together, they provide a basic supply for 1–4 plants throughout the entire cycle. Biobizz is known for its 100% organic, plant-based formulas that are easy to use. The Try-Pack is essentially a complete, worry-free package for trying out the Biobizz range.

Advantages: Very beginner-friendly – ​​an included fertilization schedule shows exactly when and how much of each component should be added. Bio-Grow ensures lush growth, Bio-Bloom provides the necessary key nutrients during flowering, and Top-Max , a humic acid-based booster, increases flower size and flavor. Many growers appreciate the naturally enhanced aromas of Biobizz in the harvest. Note: Biobizz products work best in soil (especially with Biobizz All-Mix or Light-Mix substrate) and less well in purely hydroponic systems because they contain organic particles.

420Flow Cannabis Fertilizer Set (Grow, Bloom & Booster)

The * 420Flow Cannabis Fertilizer Set is another complete package, especially interesting for beginners. It includes three 500 ml bottles – a grow fertilizer for the growth phase, a bloom fertilizer for flowering, and a booster for flavor and resin production. According to the manufacturer, the formula is vegan (no animal ingredients) and developed in Germany. However, this is not a classic organic fertilizer, but rather a mineral set (quickly available, but not purely organic). It can be used up to three times per week for maximum results. .

Pros: Everything you need is included – the kit covers the entire plant life cycle, and the application is clearly described in an enclosed diagram, giving beginners confidence. The booster is a nice extra to give the flowers an extra boost at the end (keyword: denser buds and a more intense aroma). The kit is also quite affordable (around €30 for a total of 1.5 L) and has been named the best value for money in several online comparisons. Cons: No measuring cup is included. – so you have to provide yourself with a suitable container or syringe for measuring.

Homegrow24 Cannabis All-in-One Fertilizer

For those who prefer simplicity, choose * Homegrow24 Cannabis Fertilizer (MyBuddy). This liquid all-in-one fertilizer is formulated for use in all stages of cannabis plant development —from propagation through growth to flowering. It's a purely organic, naturally-derived fertilizer (no chemical additives), enriched with secondary nutrients such as sulfur and magnesium, as well as live soil microorganisms. It comes in a 500 ml bottle, which is sufficient for numerous waterings.

Advantages: Simplicity – no need to switch between grow and bloom bottles. Smaller grows (e.g., 1-2 plants) in particular benefit from having to prepare only one nutrient solution. The organic composition improves the soil and reduces the risk of over-fertilization. Furthermore, the Homegrow24 fertilizer can be used both indoors and outdoors and, according to the manufacturer, is also suitable for other plants in the garden. Note: With all-in-one fertilizers, the dosage should be adjusted slightly depending on the phase (e.g., apply a slightly higher amount during flowering than during the growth phase, as recommended by the manufacturer) to achieve optimal results.

Hesi Blüh Complex (mineral flower fertilizer, optional)

As an optional tip for advanced growers, we'd like to mention Hesi Blüh Complex . This mineral fertilizer is a long-time favorite on the market and specifically designed for the flowering phase in soil. In addition to phosphorus and potassium, Hesi Blüh Complex also contains nitrogen, as well as important trace elements and vitamins to prevent deficiencies during flowering. Why is it optional? Mineral fertilizers like Hesi work quickly and can promote very high yields, but require precise dosing and pH control for optimal results.

Advantages: Proven quality – many experienced growers swear by Hesi for reliable results and robust flowers. Hesi Bloom Complex is also relatively inexpensive and concentrated (only a few ml per liter of water is needed). Disadvantage: Not organic, meaning you should rinse thoroughly (with pure water) at the end of flowering to flush out any fertilizer residue and avoid impairing the flavor. Not recommended for beginners unless you've done a lot of research.

TA Pro Organic Bloom (organic bloom fertilizer, optional)

Another possible candidate is TA Pro Organic Bloom (formerly GHE). This organic bloom fertilizer is certified organic and is particularly suitable for those who also want to use organic fertilizer in hydroponics or coco—because the Pro Organic series is also suitable for soilless systems. Pro Organic Bloom provides a balanced nutrient profile for blooming and is often used together with Pro Organic Grow as a two-component system.

Advantages: High purity and quality – Terra Aquatica (TA) is known for its stable, non-settling formulations. The fertilizer contains plant extracts, humic acids, and naturally occurring microorganisms that enhance nutrient uptake. When combined with organic soil or tea preparation, it can produce high-quality, aromatic buds . This fertilizer is a great choice for organic growers who want to maximize the flowering phase. However, it is somewhat more expensive and (like all organic fertilizers) requires good aeration in the tank when used in hydroponics.

Best grow fertilizer for the growth phase

During the growth phase (also called the vegetation phase), you lay the foundation for a successful grow. The best grow fertilizer is one that provides your plants with sufficient nitrogen and other nutrients during this time without overtaxing them. Specialized cannabis growth fertilizers , such as Granny's Weed Grow Fertilizer or Biobizz Bio-Grow (from the Try Pack), have proven effective. These are precisely tailored to the growth needs . It's important to fertilize early enough but in moderate doses: Starting with a low dose about two weeks after germination/cutting and gradually increasing the dose will prevent nutrient deficiencies from the start.

Mineral alternatives for the growth phase include Hesi TNT Complex (for soil) or Canna Terra Vega – these deliver fast results but require more attention to dosage and pH. Beginners are often happier with organic grow fertilizers because they are more forgiving . Ultimately, the best grow fertilizer will suit your setup: organic is better for soil and organic grows, and perhaps a two-component mineral fertilizer for hydroponics. Always ensure a balanced nutrient supply during this phase – it determines how robust and large your plants will become, which directly influences the amount of flowers later on.

Best flowering fertilizer for strong flowers

As the plant enters the flowering phase , its needs change. Now it's time for bloom fertilizer —rich in phosphorus (P) and potassium (K) to stimulate the formation of buds, resin, and flower mass. The best bloom fertilizer ensures rich, aromatic flowers without overtaxing the plant. We recommend ourGranny's Weed Bloom fertilizer for organic growers or, alternatively, Biobizz's Bio-Bloom . Both organically provide everything needed for healthy blooms and even improve the taste and aroma of the final product.

Those who prefer a purely mineral-based approach can opt for classics like Hesi Bloom Complex (as mentioned above) or Advanced Nutrients bloom formulas with balanced PK ratios. In addition, many experienced growers use special PK boosters (e.g., PK 13/14 from Canna or the organic version of Top-Max) in late flowering to give the final flowering boost. It's important with any bloom fertilizer: observe your plant. If the lower leaves turn yellow prematurely, there may be a lack of nitrogen (then add a little more grow fertilizer); if the buds remain small or foxtail, consider increasing the phosphorus. A good bloom fertilizer makes it easy – follow the schedule, and your plants will get exactly what they need for plump buds. Don't forget: In the last 1-2 weeks before harvest, only give water (flushing), regardless of the fertilizer you used, so your flowers ripen properly.

Best outdoor fertilizer for hemp plants

Outdoor cultivation requires different conditions than indoors: larger soil volumes, weather conditions, and often longer growth periods. The best fertilizer for outdoor hemp should therefore be long-lasting and robust . Many outdoor growers rely on organic fertilizers because they improve the soil and replenish nutrients over time. Products like Granny's Weed Grow/Bloom or the Green Home Set work very well outdoors—you can simply add them with your watering when it's not raining. The advantage: Natural rainfall and soil life release organic fertilizers slowly, ensuring the plants are continuously supplied.

Additionally, you can enrich the soil outdoors in advance with compost, worm castings, or guanokalong (bat manure) to provide basic fertilization. During the growth phase, an occasional growth fertilizer may be sufficient (e.g., once a week), and during the flowering phase, increase the amount of bloom fertilizer to 2-3 times a week, depending on the plant's needs. Another tip for outdoors: pelleted slow-release fertilizers (such as organic outdoor fertilizer pellets) can be mixed into the soil. These release nutrients over several months and are ideal for guerrilla grows where constant refertilization is not possible. Overall, plants outdoors can forgive a little neglect, but with the right fertilizer at the right time, you can significantly increase harvest yields even outdoors.

Organic vs. mineral – which suits your grow?

Organic fertilizer or mineral fertilizer – this decision divides the grower community. Both have advantages and disadvantages, and what "fits" depends on your goals and setup.

• Organic : Organic cannabis fertilizers consist of natural ingredients (plant extracts, compost, manure, algae, etc.). They are first converted into plant-available nutrients by soil organisms, so their effect is slower , but gentler and more sustainable . Advantages: reduced risk of overfertilization, improved soil structure, often a better flavor in the final product (many say organic weed tastes softer and "earthier"). Furthermore, with organic fertilizers, you don't have to pay as much attention to pH or EC levels—the soil life buffers a lot. Disadvantages: Less immediate control; in the event of problems (deficiencies), correction takes longer, and yields may be somewhat lower than with high-end mineral supplements.

• Mineral (synthetic) : Mineral fertilizers contain nutrients in a pure, readily available form (salts). The plant can absorb them directly, leading to rapid growth and potentially larger yields . You can control what the plant receives quite precisely (a must, especially in hydro setups). Disadvantages: Precision is required here – overfertilization happens more quickly and can burn the roots. You have to keep an eye on the pH and EC , as mineral salts can quickly acidify or salinize the soil. Furthermore, organic enthusiasts argue that mineral fertilizers harm soil life and could impair the terpene profile (flavor) of the buds.

What's right for you? If you're a beginner or value natural methods, organic is often the more relaxed route. However, if you have hydroponic systems or want to squeeze every gram of yield out of them and aren't afraid of technical fine-tuning, then mineral fertilizers are your tool. There are also mixed forms: Some growers, for example, use organic soil and base fertilizer, but add a mineral PK booster during flowering to combine the advantages of both worlds. It's important not to mix wild experiments that sabotage each other (e.g., soil culture with lots of organic material and a purely hydroponic fertilization regimen can lead to nutrient blockages). In general, knowledge of your products and an eye on the plants are crucial, no matter which approach you choose.

Beginners vs. advanced – which fertilizer is suitable for whom?

Not every fertilizer is equally suitable for every grower. It depends on your experience and how complex you want your nutrient management to be.

• Beginners: If you're just starting out with cannabis cultivation, you probably want it to be simple and forgiving . A premixed cannabis grow kit (like the Granny's Weed 2-Phase Kit or 420Flow Kit) is ideal—you get everything you need with instructions, and all you have to do is follow the plan. All-in-one solutions like Homegrow24 are also convenient for beginners, as you don't have to coordinate multiple products. Be careful to underfeed rather than overfeed in the beginning ( "less is more" ) until you get a feel for the plants. Organic fertilizers are more forgiving of application errors, so they are often beginner-friendly. Avoid particularly concentrated professional fertilizers or extensive nutrient lines with 5–10 bottles—this can be overwhelming.

• Advanced growers: Once you've already had a few successful grows, you can be more experimental. Mineral multi-component fertilizers (e.g., 3-part systems like those from Advanced Nutrients or Canna with Vega/Flores plus boosters) allow you to precisely control nutrients and push the limits. Advanced growers often have their preferred method: some swear by completely organic methods using home-brewed teas or super soil, others rely on highly bred mineral fertilizers in a hydroponic tent. It's important to recognize the needs of your strain —for example, some sativa-dominant strains require less nutrients, while indica-dominant varieties tolerate more. As an experienced grower, you can adjust fertilizers specifically: for example, add a PK booster in week 3 of flowering, or immediately add the appropriate supplement (CalMag, iron, etc.) at the first signs of deficiency. In short: Advanced growers should choose their fertilizer based on the motto “maximum control,” while beginners should go for “maximum simplicity.”

Finally, if you're a beginner, don't be afraid to use more advanced products if you're willing to learn—most manufacturers offer fertilization schedules and support. Conversely, even professionals can achieve top results with simple organic fertilizers. Know your own skill level and choose a fertilization system that's comfortable for you.

FAQ: Frequently asked questions about cannabis fertilizers

1. How often should I fertilize my cannabis plants?
This depends on the growth phase and the fertilizer used. During the growth phase , fertilizing once or twice a week is usually sufficient (perhaps a little more frequently and in smaller doses with organic fertilizer). During the flowering phase , nutrient requirements increase, so two to three times a week is fine. Mineral fertilizers are often applied every other watering, while with liquid organic fertilizers, a smaller amount can be added with each watering. Important: Follow the manufacturer's recommendations and observe the plant's reaction . If the leaf tips turn yellow/brown ( nutrient burn ), reduce the amount of fertilizer.

2. When should I start fertilizing?
Fertilization is usually not necessary for the first 1-2 weeks after germination or with young cuttings, as the plant meets its needs from the nutrient reserves in the seed or the potting soil. As soon as the plant has a few pairs of true leaves (approximately week 2-3), you can start with a mild fertilizer solution—often starting with half the dosage. If you potted in pre-fertilized soil (e.g., grow soil with starter fertilizer), wait about 3-4 weeks before adding liquid fertilizer, as this soil already contains nutrients. Rule of thumb: It's better to start a little later than too early—young plants are sensitive to overfertilization.

3. Can I use regular plant fertilizer or tomato fertilizer for cannabis?
In principle, you can also use a universal or tomato fertilizer, as the basic nutrients are similar. However, cannabis fertilizers are specifically tailored to hemp and make your life easier. For example, tomatoes generally don't need quite as much nitrogen during the growth phase as cannabis – a cannabis grow fertilizer provides exactly the optimal proportions. Furthermore, specialty fertilizers often contain additional trace elements and a pH buffer system adapted for cannabis plants. If you're in a pinch, a universal fertilizer won't hurt, but for best results (especially during flowering, when cannabis has different needs than, for example, houseplants), a targeted cannabis nutrient is definitely worth it.

4. What does NPK mean and what ratio is correct?
NPK stands for the main nutrients nitrogen (N) , phosphorus (P) , and potassium (K) , and the ratio indicates how much of each the fertilizer contains. Example: NPK 4-1-4 means 4 parts nitrogen, 1 part phosphorus, 4 parts potassium. In the growth phase, fertilizers with more nitrogen are preferred (e.g. 4-2-3), while in the flowering phase, more phosphorus and potassium are preferred (e.g. 2-4-5). Cannabis "eats" more N in the veg phase and more P/K in flowering. A grow fertilizer therefore often has a higher N ratio, while a flowering fertilizer has a higher P and K ratio. Pay attention to these numbers when buying fertilizer - they tell you which phase the fertilizer is intended for. Many manufacturers also print "Grow" or "Bloom" directly on the bottle, corresponding to the NPK ratio.

5. Should I flush my plants before harvesting?
Yes, it's generally recommended to stop fertilizing about 1-2 weeks before harvest and to only water the plants with clean water (this is called flushing ). This allows the plants to use up any remaining nutrient salts in the leaves and flowers. This leads to a better flavor and a smoother smoke, as fewer fertilizer residues remain in the dried weed. Flushing is especially important when using mineral fertilizers – here, the substrate is often rinsed with plenty of water to wash out excess salts. With purely organic cultivation, flushing is not quite as critical, but it won't do any harm. Make sure to continue watering the plants well during the flushing phase and avoid stress. Slight yellowing of the leaves towards the end is normal – a sign that the plant is using up its reserves (which is exactly what we want).

6. What can I do if there is over-fertilization or deficiency?
Over-fertilization is often indicated by burnt leaf tips, very dark foliage, or stunted growth. In this case, rinse the plants immediately with clean water (with potted plants, let a lot of water run slowly through the pot to wash out excess nutrients). Then stop fertilizing for a few days until the plants have recovered. In the case of nutrient deficiencies (yellow leaves, red stems, spots), it helps to first identify which nutrient is missing – often it is nitrogen (uniform yellowing from the bottom up), magnesium (yellow leaves with green veins), or calcium deficiency (brown spots). In such cases, you can specifically add a CalMag additive or increase the fertilizer dosage slightly, depending on the situation. It is important to prevent problems: stick to the fertilization schedule, regularly check the pH and EC (with mineral fertilizers), and pay attention to signs on the leaves. If you react early, many nutrient problems can be resolved without the harvest suffering.

Finally, observe your plants —they'll "tell" you what they need. With the tips and recommendations in this guide, you'll be well-equipped to choose the best fertilizer for your cannabis plants in 2025 and have a successful, productive grow season. Happy Growing!

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