Best Fertilizer and Compost for an Outdoor Setup

Last updated: June 2026

Fertilizers are essential for the growth of your cannabis plants. But more importantly, feeding your crops properly with the proper nutrients can help increase your yields during harvest season.

But when choosing which fertilizers to use for marijuana plants, including those grown outdoors, there are no hard and fast rules to follow. When it comes to selecting fertilizers for outdoor marijuana plants, you have to take into account a few factors, including the cannabis strain you are planning to grow, substrate type, and growth stage.

What Are Fertilizers?

Before delving deep into the nutritional needs of cannabis plants, it is a good idea to start with a few basic concepts first. To start off, you need to understand what fertilizer is.

In a nutshell, fertilizer refers to natural or manufactured substances applied to the soil surface (or other substrates) that plants use for food. The nutrients in a fertilizer allow a plant to grow healthy and aid in various functions, from foliage development to flowering.

For a cannabis cultivator, fertilizers are essential in growing marijuana plants. Without the nutrients contained in fertilizers, your crops won’t be able to reach their full potential. Your weed plants may grow even without feeding them the proper nutrients. But existing and thriving are two different things.

Suppose you supply your marijuana plants with the proper nutrients at the correct ratios and times. In that case, your plants can produce more buds with better taste and aroma.

Chemical vs. Organic Fertilizers

Fertilizers can be broadly categorized into organic and synthetic or chemical. Here is a brief description of the two.

Synthetic chemical fertilizers

Synthetic fertilizers refer to chemically-formulated products that contain the appropriate ratios of nutrients for each marijuana growth stage.

One great thing about this type of fertilizer is that its nutrients are readily available and can be used by your crops for plant growth. And because these nutrients are ready for use, this fertilizer is perfect for correcting nutrient deficits.

Finally, chemical fertilizers are best suited for cannabis fertilizers, whose primary goal is to produce thick, sticky buds.

Organic fertilizer

Organic fertilizer is a broad term for various mineral and plant-derived substances, including animal waste and compost. This type of fertilizer has been used for plant growth and health for ages, thus assuring you that it works. Some organic fertilizers must be composted or prepared before applying them to the soil surface.

Choosing between organic and synthetic fertilizers

Not sure which type of fertilizer to use? Here are a few key points to consider.

When it comes to being ready for plant use, synthetic fertilizers have the advantage over organic fertilizers. However, using synthetic fertilizers carries a few risks. For one, you need to follow the manufacturer’s instructions carefully. Otherwise, giving your plants excess nutrients can lead to nutrient burn, harming your cannabis plants.

You should strongly consider using organic fertilizers to take a more eco-friendly approach. Note that it may take some time before organic materials can be used after applying them to the soil surface. Animal manure, for example, needs to undergo the composting process before use.

At the end of the day, both chemical and organic fertilizers help grow cannabis plants. Your choice will boil down to your budget and personal preferences.

What Nutrients Do Cannabis Plants Need?

Cannabis plants need a diverse array of nutrients in varying quantities. These nutrients can be classified either as macro or micronutrients.

Cannabis macronutrients

Macronutrients refer to nutrients that weed plants need in large quantities.

On the one hand, almost all plants need carbon, oxygen, and hydrogen. The good thing about these nutrients is that your crops can get these from the air and water. To ensure that your cannabis plants get sufficient nutrients, you must facilitate proper airflow in the soil, and your grow room and provide your plants with potable water.

Aside from carbon, oxygen, and hydrogen, marijuana plants need three key macronutrients: nitrogen, phosphorus, and potassium or NPK.

1. Nitrogen

Nitrogen plays a crucial role in the production of chlorophyll. In turn, plants require chlorophyll for the process known as photosynthesis. This nutrient is essential during the vegetative stage of cannabis plants. Aside from photosynthesis, nitrogen is necessary to develop a cannabis strain’s desired traits.

1. Phosphorus

Weed plants need phosphorus during all of the growth stages. However, phosphorus is vital during the flowering stage because it aids in the development and growth of buds and in increasing their cannabinoid content.

1. Potassium

Potassium is critical for various plant functions, from the creation of plant food and energy storage.

Secondary macronutrients

Aside from NPK, cannabis plants also need larger quantities of calcium, sulphur, and magnesium.

1. Calcium

Calcium is essential both for plant development and cell strength. Without adequate calcium, your cannabis plants will have stunted growth.

1. Sulphur

Like other macronutrients, sulphur plays different roles in cannabis plant development and growth. It is important for root development, chlorophyll production, plant metabolism, and nutrient absorption.

1. Magnesium

Without magnesium, cannabis plants cannot produce sugar from photosynthesis. Aside from that, the nutrient allows plants to use glucose for growth.

Cannabis micronutrients

Although micronutrients are essential to overall cannabis plant health and development, your crops require these in smaller quantities. Some micronutrients weed plants need are silica, copper, boron, manganese, iron, zinc, and molybdenum.

How to Fertilize Your Cannabis Plants

Cannabis plants need specific nutrients at the correct ratios at each growth stage. As such, it is critical to map out a feeding schedule that details your watering and fertilization schedule.

Please note that you must give your plants fertilizers each time you water them. Doing so will only lead to nutrient lockout. Not to mention, you can end up wasting your money and doing more harm than good.

For outdoor marijuana plants, you should add fertilizers to the soil before your weed seeds germinate. Alternatively, you can add nutrients to the ground before transplanting your seedlings.

The packaging of fertilizers indicates how much nitrogen, potassium, and phosphorus they contain. For example, if the label says 10-4-4, it simply means that the product contains 10% nitrogen, 4% phosphorus, and 4% potassium.

During the vegetative stage, cannabis plants need more nitrogen than potassium and phosphorus. But once your plants enter the flowering stage, they need more phosphorus and potassium.

Cannabis fertilizers are often classified either as grow or bloom. Grow fertilizer solutions are typically given during the vegetative phase, while bloom fertilizers are best given during the flowering stage.

When to start feeding cannabis plants

You do not need to fertilize weed seeds. But once your seedlings have developed two to three sets of leaves, you can start feeding them with fertilizers. Some manufacturers recommend starting the feeding schedule a week after germination.

In feeding your cannabis plants, err on the side of caution and follow the manufacturer’s recommendation to prevent harming your young plants.

Should you use fertilizers every time you water your plants?

That depends on the product you are using. Some fertilizers should be given to cannabis plants every time you water them. And some are formulated to be used only once a week. Be sure to check the manufacturer’s recommendations.

When to switch to bloom fertilizers

As a rule of thumb, you should switch to using bloom fertilizers once you notice the early signs of the flowering stage. However, some cannabis cultivators change during the fourth or fifth week of the vegetative stage as this encourages their crops to flower earlier.

On the other hand, if you prefer that your plants stay in the vegetative stage for a longer time, you can switch to bloom nutrients once you see that your crops have grown sufficiently to fit their growing environment.

What Is Composting?

Like using fertilizers to feed your cannabis plants, composting is another practice that benefits almost all types of plants, whether cultivating veggies in a garden bed or marijuana in an indoor setup.

But what exactly is composting, and how can cannabis cultivators benefit from it?

Cannabis and healthy soil

Healthy soil is the foundation for the growth and development of your cannabis plants. Remember, your crops draw nutrients from the soil. However, the amount of nutrients soil can hold dwindles over time. And if you reuse soil for multiple seasons, eventually, its nutrients get depleted.

This is where composting comes in handy. Through composting, you can replenish the nutrients lost from the soil. Another great thing about composting is that you do not need to spend a small fortune to feed your weed seeds through various stages of development. In fact, you can go through the composting process without paying any money. You can make your own compost using things around your home, including food scraps, grass clippings, yard waste, and other organic waste.

The benefits of using compost on your cannabis plants

Composting offers a few distinct advantages. For starters, it provides much-needed nutrients back into the soil. Aside from that, composting facilitates the growth of beneficial microorganisms that aid in developing and protecting garden beds and outdoor cannabis.

Compost attracts other helpful organisms, like beneficial worms that prey upon harmful worms. Mycorrhiza, a type of fungus, helps cannabis plant roots get nutrients from the soil by breaking down organic matter.

Compost can also be considered a type of organic fertilizer. Unlike synthetic fertilizers, compost releases nutrients into the soil slowly. That means there is practically no risk of your plants getting damaged by excess nutrients. And finally, compost can alter the soil structure and texture, making it more conducive to air circulation.

How to use compost

Before outlining the steps you need to undertake to apply compost, there is one crucial thing that you need to understand. Compost is used differently from fertilizers. With fertilizers, your goal is to feed your cannabis plants with the nutrients they need. Compost, on the other hand, is used to enrich the soil, creating the right environment for the growth of weed seeds until they reach full maturity.

One key reason why some cannabis cultivators, especially the new ones, have a hard time growing weed plants is that they use poor-quality soil. Compost revitalizes the soil, providing the optimum conditions in cannabis and vegetable gardens.

Using compost is a straightforward process. All you have to do is put it on the soil surface. The amount of compost you need will depend heavily on the soil’s condition and nutrient content. Because compost releases nutrients slowly, most cannabis growers apply it to the soil around fall to ensure it will be ready by springtime. You can also use compost during the different stages of cannabis growth to ensure your plants get the necessary nutrients and minimize using fertilizers.

You can also create compost tea consisting of water and humic acid derived from compost. Compost tea can feed your cannabis plants as a foliar spray that can prevent diseases.

Composting Process 101

When you make your own compost, you mimic the natural decomposition of organic matter in the soil. In nature, microbes break down animal and plant matter into nutrients that support new life.

To start your compost pile, you must find a suitable location that is warm and away from people. Be aware that compost emits a distinct smell. Another critical factor to remember when choosing a location for a compost pile is that it should be accessible, preferably near a water supply.

Although some people can compost during the cooler months, it is best to start a compost pile during the latter months of spring or the start of summer. You can make compost even during fall, depending on where you live and the prevailing conditions. Finally, avoid placing your compost pile near your home or wooden structures, as these may be affected by the breakdown of the organic materials nearby.

Once you have found a suitable location for your compost bin, you can move on to the next step, building a base. The simplest way is to use plastic containers with holes at the bottom and the sides. These holes are essential for composting because they help retain heat and moisture. Aside from plastic bins, you can also use other materials like wood.

Another option to consider is buying a compost tumbler. A compost tumbler makes mixing and turning your compost materials easier, especially before your compost matures.

To start making, you must collect dried leaves, grass clippings, and carbon-rich materials such as straw, wood chips, sawdust, dried twigs, untreated cardboard, and paper towels. The dried leaves and grass clippings should comprise about 60 percent of your compost pile. The rest can include green plant matter.

Next, you will need to add things that are rich in nitrogen. These include grass clippings, food scraps, vegetable scraps, and animal manure. After that, you must add soil or potting mix free from synthetic chemicals.

Over time, these materials will decompose and break down into the nutrients your cannabis plants need. Be sure to check your compost pile occasionally, stirring it and adding water if you notice that the compost begins to dry.

Making compost requires little time and hard work. The microorganisms in the compost pile will do most of the heavy lifting for you. However, it would help if you turned the compost pile to hasten the process. It can take six months to two years for your finished compost to be ready for use.

The Importance of Choosing the Right Soil for Cannabis

Fertilizers and compost can only do so much to create the right growth conditions for your cannabis plants. This is why getting the best headstart with high-quality soil for your weed seeds is essential.

However, that is often easier said than done. The sheer number of options available further complicates things. As such, it is a good idea to know what type of soil to use for marijuana cultivation even before you buy weed seeds.

Qualities of the best soil for cannabis

Here are a few essential things to consider to help you choose the best soil for your weed plants. Take note that there is no best soil for all cannabis strains. And in the same vein, you can’t grow different strains using the same soil type.

1. Drainage

Marijuana needs soil that provides a good amount of drainage. How do you know if the soil has a decent amount of drainage? Pour water on the surface of the ground. If the water pools, then it means that the soil lacks drainage. Without sufficient drainage, your plants will face many issues, including death.

1. Texture

A good soil for cannabis is loose and light to the feel. This is critical for the growth and development of the roots as well as proper aeration.

1. Water retention

Although drainage is essential for the health and development of cannabis plants, the soil you use should be able to retain a good amount of water.

1. pH level

Cannabis plants require a soil pH level between 5.8 and 6.3. If the pH level is substantially higher or lower than this range, there is a considerable risk that your plants will die.

1. Nutrient content

Typically, the soil’s nutrients deplete around three to four weeks after use. You can replenish the nutrient content of the soil by using compost and fertilizers.

Soil amendment

Sometimes, you can only work with readily available soil. With soil amendment, you can improve the quality of the soil to make it more useful for your crops. Among the most commonly used materials for soil amendment are coco coir, perlite, clay pebbles, vermiculite, and worm castings. You can also use compost to amend the soil with the added benefit of infusing nutrients.

Using Fertilizers and Compost for Weed Plants

Can you use fertilizers and compost to ensure that the nutritional needs of your cannabis plants are met? It is not a good idea to use synthetic fertilizers with compost. Doing so will damage the delicate environment within the soil. You can, however, use organic fertilizers with compost.