Medically Reviewed by
Jason Crawford

Article Last Updated on January 3, 2023

Every marijuana grower strives to have healthy weed plants that grow big and result in a THC-rich yield. The most important factors for healthy plant growth are good soil, adequate lighting, enough grow room, and water. And these factors differ depending on whether you’re growing your plants outdoors or indoors in grow tents.

But even if you do everything by the book, your marijuana flower might nevertheless suffer from nutrient deficiency, and you may be wondering whether you should use Miracle-Gro (often referred to as Miracle Grow) in order to increase the number of nutrients and help your cannabis plants thrive.

Given that every marijuana plant’s need is different, your plants will probably need a specific marijuana fertilizer. This will vary depending on the type of cannabis you’re growing (Indica, Sativa, or hybrid) and the type of plants you have (auto-flowering or photoperiod).

What Nutrients Do Your Cannabis Plants Need?

Every cannabis plant needs to have an adequate amount of micro and macronutrients in order to grow into a healthy plant.


The most vital macronutrients needed for optimal plant growth are Nitrogen (N), Phosphorus (P), and Potassium (K), or NPK as it’s often displayed on fertilizer packaging. Healthy plants need all three nutrients in order to have vibrant flowers and high yields, but each plant requires different amounts of them.

Nitrogen is important for photosynthesis, chlorophyll production, and leaf growth. Phosphorus promotes seed germination, root growth, and bud growth, and is also crucial for the development of terpene resins. Potassium, on the other hand, is important for a healthy plant metabolism during the flowering period and helps in the formation of the clusters of marijuana flowers.

Potting soils already contain these three nutrients, and they will aid the growth of the plant for up to three weeks. Afterwards, the plant needs to receive additional nutrients in the form of fertilizer or as a hydroponic solution.


Micronutrients are also important in order to cultivate a healthy marijuana plant. The most important ones are Calcium, Magnesium, Sulphur, Manganese, Boron, Zinc, and Copper, and small amounts of them are found in most fertilizers. Together they strengthen the stems and branches, stimulate the formation of chlorophyll, produce plant proteins and enzymes, help with water consumption by the cells, and help in the formation of stems, stalks, and buds.

Other micronutrients that are important are Zinc and Copper which strengthen and fortify the stems, branches, stalk, and leaves and promote the growth of young leaves.

While having a lot of nutrients can lead to plants experiencing nutrient burn and result in a burnt plant, not having enough nutrients will result in a nutrient deficiency, so it’s important to provide your plant with a balanced amount of nutrients.

As we went through the most important factors that enable optimum plant growth, let’s get into how and if Miracle-Gro can help marijuana plants grow.

What Is Miracle-Gro?

Miracle-Gro is a plant fertilizer that was first developed in the late 1940s by Horace Hagedorn and Otto Stern, and it’s still used to this day. It’s one of the most famous plant foods in the world that’s used to provide houseplants with additional nutrients by applying it in the soil. The main ingredients of this fertilizer are nitrogen, potassium, and phosphorus, and as a result a lot of marijuana growers believe that it’s a good option to use as a cannabis fertilizer as well.

Can You Use Miracle-Gro to Fertilize Your Marijuana Plants?

A lot of first-time growers use Miracle-Gro when cultivating their first cannabis plants, but you shouldn’t do this for the following reasons.

While some growers report positive experiences from using Miracle-Gro, this can only happen in the beginning phases of growth and by using a watered-down solution. The problem is that the standard Miracle-Gro formula isn’t adequate for the entire plant’s life cycle and its different stages of growth. Therefore, Miracle-Gro won’t be suitable for the flowering stage since the plant needs a different ratio of nutrients between seedling and full flower. 

The other problem is that the Miracle-Gro blend contains slow-release Nitrogen which may harm the plants, reduce the yields in the final flowering stage, and give the plant an unpleasant chemical taste. As a result of that, many growers choose better soil or coco coir.

Marijuana Fertilizers to Use Instead of Miracle-Gro

If you’re cultivating your own marijuana plants, there’s a high chance you’re going to need to use some sort of additive in the process, especially if you’re a newbie grower. One of the options is to use a natural fertilizer which is what most experienced growers do, or use a store-bought one.

Natural Ways to Fertilize

  • Coco coir. This is an easy-to-use growing medium that is inert (it has no nutrients in it) so it requires adding extra calcium and magnesium, the pH needs to be maintained between 5.5 – 6.5, and extra water needs to be added.
  • Wood ashes. These are a good option as a natural fertilizer since they contain good amounts of potassium and lime.
  • Composting. Including compost in your marijuana soil is a good way to enrich the soil and boost the growth of the plant.
  • Bat guano. This is good for the vegetative stage since it has an NPK ratio of 10:3:1.
  • Worm castings. They protect the marijuana plants from pests and diseases without using chemicals as this Cornell study shows

Store-Bought Fertilizers

  • Fox Farms Trio: This is a good way to prevent calcium and magnesium deficiencies in plants. The FF trio contains “Grow Big,” “Tiger Bloom” and “Big Bloom” which is suitable for all marijuana strains. In order to get the best results, follow the feeding schedule provided by Fox Farms.
  • Bergman’s Plant Food: This is another easy option for marijuana growers since the company offers different fertilizers for the different growth periods. There’s one for the seedling, one for the growing period, and one for the flowering period.
  • Perlite and vermiculite fertilizers: This is the best option for experienced growers since it gives a professional quality soil. It’s important to remember that you’ll need a different concentration of perlite and vermiculite for hydroponic and soil growing methods, and often peat moss is added to the mix. 

Fertilizing Autoflowering VS Photoperiod Cannabis Plants

For autoflowering strains, you should opt for soil that isn’t heavily fertilized. Your best bet would be to use a mix of 50% soil to 50% coco coir to help with water retention. To that, you might add peat-based soil with perlite in order to ensure good drainage. The fertilizer should generally be added at a later stage when the plant is bigger.

Photoperiod strains should be started in small seedling pots with soil that has no nutrients. After a few weeks, they should be replanted. Nutrients may be added to more mature plants.

The 411 on Using Miracle-Gro for Cannabis Growing

Generally, Miracle-Gro is suitable for plants with simple grow-cycles, and since marijuana isn’t one of those plants, it probably won’t be a good fit.

Growers who report positive experiences from using Miracle-Gro typically use a watered-down solution since this fertilizer provides a one-size-fits-all approach that doesn’t align with the different stages of growth of the cannabis plant. By trying to fertilize with it, you risk ruining your plants.

Your best option would be to use a natural homemade fertilizer for weed, which is the go-to method for experienced cultivators, or use a store-bought fertilizer if you’re cultivating for the first time.

A passionate advocate for the benefits of cannabis. Fraser Horton, who has a background in botany and a strong love of nature, has spent years researching how cannabis affects the body and mind. He established Leaf Nation in 2020, where he has devoted himself to educating people about the legalisation of marijuana and its safe and responsible use. Fraser is committed to highlighting cannabis’ potential for improving wellness and working to dispel the stigma associated with its use.


The information presented on this page is provided as a public service to aid in education and is derived from sources believed to be reliable. Readers are responsible for making their own assessment of the topics discussed here. In no event shall Leaf Nation be held reliable for any injury, loss or damage that could happen if using or abusing drugs.