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Top Dressing Cannabis Plants: A Complete Guide

Using synthetic fertilizers is a quick and easy way to feed cannabis plants; however, it does little to support the ecosystem or structure of the soil. In contrast, top dressing with organic amendments allows you to fertilize cannabis plants while improving soil quality.

There are many ways to top dress plants, ranging from beginner-friendly to complex. In this article, we’ll discuss why you should top dress cannabis plants and how to use this method to enrich your soil.

Why Synthetic Fertilizers Can Harm Soil Health

Synthetic fertilizers are great at supplying plants with an immediate dose of nutrients. That’s because they contain mineral salts that rapidly dissolve in water. As a result, plants can absorb these nutrients much faster than they can uptake organic inputs. This sounds great, but over time, mineral salts might cause more harm than good.

As the field of soil science continues to advance, many growers are beginning to understand the importance of building a soil-food web to support the growth of cannabis plants. This network of bacteria, fungi, and other beneficial microbes aids plants in a variety of ways, including enhancing nutrient uptake and root growth, protecting against pests and pathogens, and much more. With this ecosystem protecting them, cannabis plants can reach their full genetic potential, yielding exceptionally and flavorful buds.

Unfortunately, synthetic nutrients have been shown to kill soil microbes. They also build up in the medium over time, creating an inhospitable environment for plants. As a result, the soil-food web breaks down, and plant health suffers. Some salt-based fertilizers have even been shown to be harmful to humans.

Growers can protect the health of their cannabis plants by replacing salt-based nutrients with dry amendments. By top dressing with compost, worm castings, kelp meal, and other organic amendments, you’ll be able to feed your plants while supporting the growth of beneficial microbes in the soil.

Benefits of Top Dressing Cannabis Plants

Top dressing with organic dry amendments is an easy, affordable, and sustainable alternative to synthetic nutrients. If you’re on the fence about trying this method to fertilize your plants, consider these benefits of top dressing:

  • Dry amendments are often more affordable than bottled nutrients
  • Organic nutrients are absorbed slowly, preventing overfertilization
  • Beneficial microbes require organic matter to survive
  • Organic amendments can improve the flavor and of cannabis
  • You can make your own customized blends of dry amendments

When To Top Dress Cannabis Plants

Before organic amendments can be absorbed, they must be broken down by the microbes in the soil. Because this process can take several days, it’s a good idea to top dress your plants before they show signs of deficiencies.

Outdoor growers should apply a top dressing to the soil in early spring. This will give the microbes enough time to break down the organic matter and release nutrients into the medium. By the time the plants have started the vegetative growth period, the soil will be ready to use. Likewise, indoor growers should let their freshly amended soil sit for a few weeks before planting.

Depending on how nutrient-dense your medium is, you may need to top dress several times throughout the season. Typically, adding amendments every two to three weeks is a good idea, especially when growing in containers. The smaller your pot is, the more often you’ll need to top dress.

Best Amendments for Top Dressing Cannabis Plants

Pre-made Blends


There are hundreds of options out there when it comes to dry amendments. For those who haven’t grown organically, it can be overwhelming to learn which fertilizers to use and when to apply them.

Using pre-made organic fertilizer blends is a simple and effective way to top dress your plants. These blends have been expertly formulated to give plants exactly what they need during various stages of growth. Brands such as Gaia Green and Dr. Earth have an assortment of fertilizer blends optimized for the vegetative and flowering periods.


Top dressing with compost is a fantastic way to improve soil health while fertilizing your plants with plenty of macro and micronutrients. You can buy compost at most garden centers or even make your own at home.

Most composts can be applied to plants at any growth stage—even during the seedling phase. They are full of microbes and organic matter, which can help to improve soil texture, buffer the pH of the soil, and supply your plants with an abundance of high-quality nutrients.

Worm Castings


As with compost, worm castings can be used during the entire lifecycle of the plant. They break down slowly, giving your cannabis plants a steady supply of nitrogen, potassium, calcium, and magnesium without burning them. It’s also fairly easy to create your own worm castings at home.

Worm castings have been shown to provide a wide range of benefits for plants, including improving flower size, bloom quantity, quality, and color. Some research has also shown that castings can prevent pests and diseases from taking hold in the garden.

Blood Meal and Bone Meal

Blood meal and bone meal are byproducts of slaughterhouses, derived from the blood and bones of cattle and hogs. These amendments may be a bit gruesome, but they are some of the most nutrient-dense organic fertilizers available.

Blood meal is in nitrogen, making it an excellent amendment for the vegetative growth phase. Bone meal, on the other hand, is ideal for the flowering period as it is in phosphorous and calcium. Bone meal also breaks down slower than blood meal, typically lasting the entire growth cycle.

Kelp Meal


Kelp meal is another nutrient-rich amendment perfect for top dressing cannabis plants. This fertilizer, derived from dried seacannabis, is in calcium, magnesium, sulfur, manganese, copper, iron, and zinc—micronutrients lacking in most soils.

Kelp meal contains auxins, gibberellins, cytokinins, and other growth hormones that can increase vigor and yield in cannabis plants. This fertilizer is also an excellent source of carbohydrates that promote the growth of beneficial microbes in the soil.

How To Top Dress Cannabis Plants

Now that you understand when to top dress and which fertilizers to use, let’s have a look at how to top dress cannabis plants.

Step One: Choose Your Amendments

To determine which amendments to use, consider your plants’ growth stage. Cannabis requires higher nitrogen levels during the vegetative growth period and more phosphorous and potassium during flowering. Look for any signs of deficiencies and adjust your amendments accordingly. Once you’ve decided which fertilizers to use, you can mix them together to create a blend or add them individually to the medium. Make sure to follow the product’s recommended dose to avoid under or over fertilizing the plants. Generally, it’s best to go lower than the recommended dose to avoid burning the plants.

Step Two: Apply the Top Dressing

After you’ve created your mixture of amendments, apply it in a thick, even layer on the top of the soil. Gently work it into the surface of the medium with your fingers or a cultivator. Don’t go too deep, or you risk damaging the roots of the plant and disturbing the microbes in the soil.

Step Three: Water in the Amendments

Next, it’s time to water in the amendments. This will ensure they are flushed down into the root zone, where the plant can absorb them. Water the soil evenly to avoid leaving any dry pockets. Keep the soil moist but not too wet to prevent the roots and microbes from being starved of oxygen.

Optional Step: Apply a Layer of Mulch

Applying a layer of mulch will insulate the medium, provide moisture retention, and protect the roots and microbes from the sun’s rays. You can use shredded or chipped bark, wood chips, shredded leaves, grass clippings, straw, or even newspaper. Add a three- to four-inch layer of mulch evenly to the top of the soil.

Final Thoughts on How To Top Dress Cannabis Plants

There you have it: our complete guide to top dressing cannabis plants. Top dressing is an easy and affordable way to improve soil health while growing frosty, flavorful, all-organic cannabis.

Have you tried top dressing your cannabis plants? Please share your experience in the comments section below. While you’re here, check out our collection of regular and feminized cannabis seeds. 

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