5 Most Important Nutrients for Autoflowers

When it comes to growing autoflowering cannabis plants, understanding their nutrient needs is essential for a successful harvest. Unlike photoperiodic plants, autoflowers have a shorter life cycle, which means they have different nutrient requirements. While they need the same 18 essential nutrients as photoperiod plants, they are required in slightly different rations at different times. Here, we’ll break down the best autoflower nutrients—and what they need to thrive.

Key Nutrients for Autoflowers

The key difference between autoflower and photoperiod plant nutrients is the ratio and application timing. Because autoflower plants begin and end their life cycle in as little as 100 days, they experience tremendous growth. It is important to keep them healthy with a well-balanced ration of nutrients. You can “crop-steer” your autoflower plants by feeding them more vegetative, higher Nitrogen ratio, or flowering nutrients, higher Phosphorus and Potassium, to influence their growth and maturity.

To maintain a balanced fertilizer your soil or growing medium needs to be rich in organic matter, if growing organically, and balanced in pH and moisture levels. Your pH should range between 6 and 7 for optimal nutrient uptake and it should be moist but not over saturated. It is important not to let your plants dry out as this can trigger premature flowering and decrease your yield.

The essential nutrients required by autoflowers are as follows:

1. Nitrogen (N)

Nitrogen is crucial for the vegetative stage of autoflowers. It promotes healthy leaf and stem growth. During the early stages, ensure your plants receive adequate nitrogen to build a strong foundation.

To learn more about Nitrogen and how we can manage it more effectively check out this podcast episode featuring the Donutz triploid that is being grown across the United States by citizen scientists for the Botanical Latitude And Zone Evaluation project.

2. Phosphorus (P)

Phosphorus is vital during the flowering stage. It supports the development of buds and flowers. Ensuring your autoflowers have enough phosphorus will help maximize your yield.

3. Potassium (K)

Potassium aids in overall plant health and improves resistance to diseases. It also helps in the development of strong, sturdy stems and enhances the plant’s ability to absorb other nutrients. Kelp is an excellent source of Potassium.

4. Secondary Nutrients

Secondary nutrients include Calcium, Magnesium, and Sulfur. They are essential for strong cell walls, efficient photosynthesis, and chlorophyll production. While Cal Mag is often touted as a fix-all for cannabis, it is important to maintain a 2:1 ratio of Cal to Mag. Adding too much of one or the other can hinder the uptake.

5. Micronutrients

Micronutrients like iron, manganese, zinc, and copper, though needed in smaller amounts, are essential for various physiological functions in plants. Silica/Silicon is often underutilized but found in abundance in nature.

For a deeper dive into the specific roles of these nutrients and how to apply them, refer to our full-length nutrient article here.

Organic vs inorganic nutrients

When it comes to choosing organic versus synthetic nutrients, you should keep in mind the difference in the growth cycle of autoflower plants. Because they grow so quickly and mature in a shorter amount of time, it is important to have accessible nutrients. You can ensure your nutrients are available to your plants by providing them with different types, both slow-release and fast-acting.

Organic Nutrients

Organic nutrients are derived from natural sources like compost, manure, and bone meal. Organic nutrients must be digested by microorganisms for the plant to access them. They release nutrients slowly, providing a steady supply over time. 

The benefits include improved soil structure and microbial activity, which can enhance nutrient absorption. However, they might take longer to show results and require careful management to avoid nutrient imbalances.

To keep things organic but provide immediate access to nutrients you can use a combination of slow-release fertilizer like Rainbow Mix alongside a water-soluble fertilizer like Organics Alive, made from fermented microbial by-products. This ensures your plant has fertilizer in the soil as well as a weekly to bi-weekly nutrient root drench to keep up with the explosive plant growth rate.  

Inorganic Nutrients

Inorganic nutrients, or synthetic nutrients, are chemically formulated to provide precise nutrient ratios. They are fast-acting and can be tailored to the specific needs of autoflowers at different growth stages. The downside is they can lead to nutrient burn if overused and may affect soil health negatively over time.

If you are using synthetic nutrients, try to reduce your run-off. This will effectively eliminate waste and reduce the ecological impact synthetic fertilizers can have on microbial life and our waterways.

Slow-release vs bottled options

When it comes to slow-release nutrients compared to bottled nutrients the main difference is the availability for the plant to use the nutrients immediately or slowly. Since autoflowers have such a short life cycle, it is important to give them both options. This allows the plants to reach their highest potential, pun intended. 

You can push your autoflowers and get a greater yield by giving them fast-acting fertilizers that often come in bottles. When you purchase a bottled nutrient, like Advanced Nutrients, you are paying for mostly water. Therefore, it is more affordable and sustainable to buy water-soluble powders that are immediately available.

Slow-release Nutrients

Slow-release nutrients gradually provide nutrients over an extended period. They are ideal for novice and experienced growers who prefer a low-maintenance approach. However, they might not be as responsive to the immediate needs of your plants.

There are slow-release fertilizers in both organic and synthetic forms. For organic you can use slow-release dry amendments like those in Rainbow Mix, and for a synthetic option, you could choose something like Beanstalk.

Remember organic nutrients require digestion from microorganisms therefore adding microbial products can increase availability, while synthetic nutrients only require water to become available. The relationship between microorganisms and plants not only provides access to nutrition but also increases your plants’ immune system and strengthens their resistance to pests and pathogens. Something that synthetic nutrients don’t offer.

Synthetic Nutrients

Synthetic nutrients offer more precision or control, allowing you to adjust feeding based on the plant’s specific needs at various stages. They are typically more responsive but require more frequent monitoring and adjustments.

To use synthetic nutrients, you need to have the correct pH and use tools to monitor the EC or PPM of the solution. You can feed your autoflowering plant based on the readings of the solution, but remember that any run-off is essentially a waste of resources as they are water-soluble and leach out with the run-off. Synthetics are often used as hydroponic nutrients. The choice of which ones to use can vary widely and depends on your personal growing style. 

How frequently should you feed autos?

Feeding frequency can vary based on the growth stage and the specific nutrient solution used. A general guideline is to feed young seedlings lightly once a week and increase the frequency as they grow. During the flowering stage, feeding can be adjusted to twice a week. Always monitor your plants for signs of nutrient deficiency or burn and adjust accordingly.

Remember if you use a combination of slow-release and water-soluble nutrients your plant will always have access to nutrients within the soil. During the vegetative phase, you can even foliar feed to boost the growth of your plants.

Autoflower Nutrient Feeding Schedule Infographic

Autoflower feeding schedule

Here’s a quick reference guide for feeding your autoflowers:

Week 1-2 (Seedling Stage)

– Nutrients: Light nutrient solution, mainly nitrogen. (100-200 PPM)

– Frequency: Once a week

Week 3-4 (Vegetative Stage)

– Nutrients: Balanced N-P-K ratio, feed higher Nitrogen to crop-steer into a vegetative stage for longer. (600-800 PPM)

– Frequency: Twice a week

Week 5-8 (Transition Stage)

– Nutrients: Increased phosphorus and potassium or both vegetative and bloom nutrients (1000- 1200 PPM)

– Frequency: Twice a week

Week 9-12 (Late Flowering Stage)

– Nutrients: Higher potassium and phosphorus, reduce nitrogen. (1200-1400 PPM)

– Frequency: Twice a week

Week 13+ (Pre-Harvest)

– Nutrients: Flush with Heavy 16 finish or similar product—anything with zero nitrogen. This will remove any nitrogen left and allow plants to consume slow-release fertilizer within the soil.

– Frequency: Three days before harvesting.

Frequently Asked Questions About Autoflower Nutrients 

What’s the best autoflower fertilizer?

The best fertilizer for autoflowers is one that provides a balanced N-P-K ratio and includes essential secondary nutrients and micronutrients including Silica. Many fertilizer companies do not include Silica in their formulation because it needs to be added to your water first as it can tie up other nutrients. Make sure you include a Silica form such as potassium silicate.

What’s the best NPK level for autoflowers?

During the vegetative stage, an NPK ratio of 10-2-2 is ideal. During transition use both vegetative and bloom or a specific transition product with 4-5-5 during the transition stage. In the flowering stage, switch to a 0-10-8 ratio to support bud development.

Do autos need more nutrients?

Autoflowers do not necessarily need more nutrients than photoperiodic plants, but they do require precise and timely feeding due to their shorter life cycle. This means paying attention to leaf color, growth cycle, and leaf size to determine when to transition from vegetative to flowering nutrients is key.

How can I maximize my autoflower yield?

To maximize yield, ensure your plants receive the right nutrients at the right times, maintain optimal pH levels, and provide adequate light and water. Avoid overfeeding to prevent nutrient burn. Transplant carefully as autoflower roots do not like to be touched.

Use a higher Nitrogen ratio through the transition phase to maintain vegetative growth. Grow in a larger container to extend the vegetative growth cycle, such as a 20-gallon fabric pot or plant directly in the ground. When planting outdoors, one foot apart for faster flowering or four feet apart for a longer vegetative phase.

Best Nutrients for Autoflowering Plants – Growing Bigger Buds

Understanding and meeting the nutrient needs of autoflowers is key to a successful harvest. By ensuring a balanced supply of essential nutrients and choosing the right feeding strategy, your plants will thrive through each growth stage. Regular feeding and monitoring can prevent deficiencies and nutrient burn, maximizing yield. With proper care and attention, your autoflowering cannabis plants will reward you with robust growth and abundant, high-quality flowers.