Complete Guide To Cannabis Nutrients: When, How Much Your Plants Need

Like us humans, plants need food to thrive, and proper nutrition is the key to happy, healthy plants. 

As a general rule, every cannabis plant needs three key nutrients to thrive — nitrogen (N), phosphorus (P), and potassium (K), but that’s not all! 

There are organic and synthetic nutrients depending on what you’re looking to achieve. Each growth phase of the plant also requires a different set of nutrients in different quantities. 

There’s much to learn about nutrients, and in this article, we’ll look at all of them! 

Best Nutrients for Each Stage of Cannabis Growth

If you’re thinking of the right nutrients to feed your plant, first, determine what stage your plant is in. 

Cannabis seedlings don’t need extra nutrients at first. They rely on the nutrients stored in the substrate and take in water through their leaves while their roots are still growing. 

To grow healthy cannabis plants, you must manage their nutrients carefully. Without the proper nutrients, the plants will weaken, become vulnerable to pests and diseases, and may not survive. 

Even if they grow, they won’t produce the large, quality buds growers aim for, which is why understanding plant nutrients is so important.

Cannabis plants rely on three main nutrients to grow well: nitrogen (N), phosphorus (P), and potassium (K). These are known as NPK ratios.

During the vegetative stage, the plants need more nitrogen but less phosphorus and potassium. 

When they move to the flowering stage, they require more potassium and phosphorus while needing less nitrogen.

QUICK NOTE: 

• If you’re using a “soil-less” potting mix like peat moss, coconut coir, and wood chips, you’ll need to add nutrients from the start because these mixes lack enough nutrients.

Aside from that, you’ll only need to feed them after about 3–4 weeks once they’ve grown 3–4 true leaves and have entered the vegetative growth stage.

Best Nutrients for the Vegetative Stage

Some growers prefer to start their plants with a mild 2:1:2 fertiliser (that’s the NPK ratio) for about a week as the seedlings transition into the vegetative phase. 

This gentle introduction helps avoid nutrient burn (more on this later). Others go straight to a 4:2:3 fertiliser to encourage faster growth right away.

QUICK NOTE: 

• These ratios are just general guidelines. If you’re using a grow kit like the Standard NPK Nutrient Kit from HomeGrown Cannabis, it’s designed to provide the perfect nutrients for your plant throughout its entire growth cycle. It also includes a feeding schedule tailored to the NPK ratios, making it easy to follow.

By the middle of the vegetative phase (around 6 weeks after germination), it’s time to increase the nutrient levels significantly. 

A 10:5:7 fertiliser is commonly used at this stage to focus more on nitrogen and support the development of strong, healthy leaves. 

The high nitrogen content at the vegetative stage promotes lush, green growth and plenty of bud sites for the flowering phase.

As the vegetative stage nears its end, it’s wise to start reducing nitrogen and preparing your plants for flowering. Many growers switch to a balanced 7:7:7 fertiliser during the last week of this phase to ease the transition.

Best Nutrients for the Flowering Stage

When your cannabis plant enters the flowering stage, it needs more phosphorus (P) and potassium (K) while requiring less nitrogen. 

These nutrients help the plant produce large, resin-rich flowers.

QUICK TIP:

• You can tell your plant is flowering when the pistils (tiny hairs) turn brown and shrivel, no new pistils grow, the calyxes swell, and under a magnifying glass, trichomes change from clear to cloudy, and finally to amber.

We can divide the flowering stage into four phases: early bloom, mid-bloom, mid-late bloom, and late bloom.

The early bloom (usually the first 2 weeks) feeding NPK of 5:7:10 fertiliser is ideal.

By mid-flowering, you gradually increase nutrients, ensuring potassium levels stay higher than the rest. By this point, most growers use a 6:10:15 fertiliser.

You want to reduce nutrient levels at late flowering to prepare for the pre-harvest flush. A lighter 4:7:10 fertiliser works well during these final weeks.

This nutrient adjustment supports healthy flower development and smooths the transition to harvest.

Now, it’s one thing to know all the quantities and types of nutrients to feed your plant; it’s another to know how to apply them and in what frequency and quantity. 

We explain that in more detail in the section below. 

How to Apply Cannabis Nutrients

Many fertiliser brands offer feed charts to help growers provide the proper nutrients to their plants at the right time. 

These charts usually outline a 12–13-week growing cycle.  

The chart’s x-axis often shows the weeks of the cycle and may include other details, like the light schedule (photoperiod) for each stage.  

For example, here’s an illustration of the ideal feeding schedule for cannabis plants in soil using a high-quality Weed Growing Kit.

Nutrient Schedules for Cannabis Growth

The main purpose of a feed chart is to tell you what nutrients to give your plants, and in what amounts during different stages of their growth. 

Fertilisers are typically mixed with water and given once a week. 

Some charts also include target EC (electrical conductivity) or PPM (parts per million) levels for accuracy. If that’s the case, using an EC meter can help you prepare the right mix.

After feeding your plants, it’s helpful to check the EC or PPM of your soil to make sure your plants are absorbing the nutrients effectively.

How to Read and Interpret Nutrient Labels

EC measures the electrical conductivity of your nutrient solution, which indicates the concentration of dissolved salts (nutrients). 

It’s usually expressed in millisiemens per centimetre (mS/cm) or microsiemens per centimetre (µS/cm).

PPM estimates the total amount of dissolved solids (nutrients) in the solution. It’s a simpler way to interpret EC, measured in parts per million.

Different plants and growth stages require different EC and PPM levels. For example:

• Vegetative Stage: EC: 1.2–1.6 | PPM: 600–800
• Flowering Stage: EC: 1.8–2.4 | PPM: 900–1200

To convert an EC reading to ppm, multiply it by 500 or 700, depending on the scale. Many EC or ppm readers can automatically do this conversion.

The lower the ppm, the less nutrient-dense your solution. 

When your cannabis plant is at the seedlings or early sprouts, stick to 100 to 250 ppm. When it grows into the early vegetative stage, ensure it reads 300 to 400 ppm. 

The full vegetative stage of the cannabis plant requires a ppm of 450 to 700, while the early flowering stage requires 750 to 950 ppm. 

As your plant grows into the peak flowering and ripening stage, ensure the nutrient scale reading goes up from 1,000 to 1,600. 

QUICK TIP:

• Always check what scale your nutrients are based on before mixing your nutrient solution.

How to Apply Nutrients in Soil vs. Hydroponics

When you grow cannabis hydroponically, you use an inert medium like coco or reservoir water as the primary medium. 

This system involves the flow of highly oxygenated, nutrient-enriched water so a desired amount goes directly to the plant’s root. 

Hydroponic nutrients are different from those used for growing weed plants in soil. 

If you grow your cannabis plant in a soil medium, the essential nutrients will not include all micro-elements because the soil already provides them naturally.

A good hydroponic nutrient mix should include all these elements: 

• Nitrogen (N)
• Potassium (K)
• Phosphorus (P)
• Calcium (Ca)
• Magnesium (Mg)
• Sulphur (S)
• Iron (Fe)
• Manganese (Mn)
• Copper (Cu)
• Zinc (Zn)
• Molybdenum (Mo)
• Boron (B)
• Chlorine (Cl)

The easiest way to get these nutrients in their correct proportions is to buy pre-formulated commercial hydroponic nutrients from local gardening stores.

Preventing and Solving Nutrient Issues

As you progress in understanding cannabis nutrients, you’ll also need to understand problems like nutrient burn and lockout. 

Cannabis Nutrient Burn

Nutrient burn happens when plants get too much fertiliser.

SYMPTOMS

You’ll notice the leaves turning very dark green, with bright, glowing green tips curl upward sharply. The stems or branches might also turn deep red, purple, or magenta.  

If the plant is flowering, its buds and small leaves (sugar leaves) may turn yellow and then quickly start to wither.  

SOLUTION

To fix this, rinse the plant’s roots with clean, pH-balanced water for about a week. Then, slowly start using fertiliser again, but in lower concentrations. 

HOW TO AVOID

Using PPM (parts per million) and EC (electrical conductivity) to track nutrient levels can prevent this problem. 

Nutrient Lockout in Weed Plant

Nutrient lockout happens when too many nutrients build up around the roots or when the pH levels are off, making it hard for plants to absorb the necessary nutrients.  

SYMPTOMS

This can cause yellow leaves, burnt tips, oddly shaped leaves, or brown spots. The exact signs depend on which nutrients the plant is missing.  

SOLUTION

To fix it, rinse the soil with clean water, check the pH levels, and adjust the nutrients as needed.

HOW TO AVOID

Regularly checking the pH of your plant’s soil is the most practical way to prevent nutrient lockout. 

If the pH is too high or too low, use a pH adjuster to fix it. Just add the solution to the soil to bring the levels back to normal and keep your plants healthy.

This leads us to the next section, which explains more about pH and how cannabis plants absorb nutrients. 

pH and Nutrient Absorption

Both pH and temperature are crucial when feeding your plants. Even a slight change in either can make it harder for plants to absorb nutrients. 

So, when it’s time to feed, make sure your nutrient solution has the pH recommended by your fertilizer brand (usually between 5.8 and 6.2) and your water temperature is between 19 21°C.

While using chemical fertilisers might seem easy, it can take some practice to get the right balance with liquid mineral nutrients can take some practice. 

With organic fertilisers, you won’t need to worry as much about pH since the soil tends to stay balanced on its own.

Organic fertilisers, like compost, worm castings, and bone meal, are better for promoting plant health. 

They help develop healthy microbes in the soil, creating a more natural environment.

Flushing Before Harvest

Flushing is when you discontinue the supply of nutrient elements to the weed plant. You also run plain water to remove excess nutrients and chemicals in the soil or any growing medium.

Flushing is typically done about two weeks before harvest, depending on your cannabis plant’s flowering cycle. 

For instance, if your plant has an 8-week flowering period, start flushing in the 6th week when trichomes turn cloudy white.  

Starting the flushing too soon deprives the plants of needed nutrients, leading to yellowing or discolouration and stunted growth. Overflushing, on the other hand, can weaken plants. 

How to Flush Cannabis Plants Before Harvest

STEP 1: Check Water pH

Ensure your water has a pH between 6.0 and 6.8 for soil-grown plants.  

STEP 2: Water Without Nutrients

At feeding time, water the plants using plain water without adding nutrients or supplements. Avoid overwatering to prevent deficiencies.  

STEP 3: Repeat After 15 Minutes

Water again to thoroughly rinse the soil

STEP 4: Test Runoff

Measure the purity of the runoff water using a TDS (Total Dissolved Solids) reader. It should match the purity of the water you’re using for flushing.  

STEP 5: Monitor Yellowing

Some leaf yellowing is normal during flushing, but harvest before the leaves on the buds turn yellow. Letting them yellow too much indicates the buds are deteriorating.  

STEP 6: Inspect Plant Color

Flushed plants should appear lighter and will be ready for harvest when all the nutrients are cleared.  

Wrapping Up

Like with other parts of growing cannabis, feeding your plants takes time and learning—you won’t get it perfect on the first day.  

It’s much easier if you stick to one brand of fertiliser or organic nutrients and follow the manufacturer’s instructions on when, how often, and how much to use on your plants.

FAQs

What Are the Best Nutrients for Bigger Buds?

A healthy plant will produce bigger buds, so focus on giving your plants the right nutrients at the right time. 

But when plants reach their mature size and begin flowering, they need more phosphorus, the nutrient most essential for flowering.

How Do I Know If My Plant Needs More Nutrients?

The common signs of nutrient deficiency are dry leaves, yellow or brown leaves, and discoloured stems. To fix nutrient deficiencies, add more nutrients or address any nutrient lockout issues first.

Can I Use the Same Nutrients for Soil and Hydroponics?

Yes, you can, but you should avoid nutrient mixes that contain nitrogen in the form of urea or ammonium. For hydroponic grows, it’s best to use fully water-soluble products that either provide nitrogen only as nitrate or don’t contain nitrogen at all.