A Beginner’s Guide to Top Dressing and Organic Tea

29 Apr 2023

If you are new to growing Cannabis indoors, and have decided to start on the organic path, then knowing about top dressing and compost tea is a big advantage. Basically, two different ways of slowly releasing nutrients back to the roots, and ensuring the microbiology in the soil food web is thriving. In this article we explain all about top dressing, the different types, break down organic compost tea, cold water extracts and much more.

What Is Top Dressing?

Top dressing is a simple way to keep your pots well-balanced with nutrients that are released slowly. The idea of a top dressing is to supplement the plants with Nitrogen, Phosphorus and Potassium as well as trace elements. When growing Cannabis organically, there will be a buffering zone of 72 hours, allowing the nutrients in the soil to be slowly broken down and easily absorbed. 

The way you apply a top dressing is to create a layer of hard food / organic substrate which is around 10 mm from the top of the surface. Once you water and feed nutrient solution, the top dressing will begin to break down into the soil. As a result, the mycorrhizal fungi and beneficial bacteria responsible for accelerated decomposition will convert the organic material into food, and interchange eat the carbon left behind as a food source. 

The Benefits of Top Dressing

The benefits of frequently adding a layer every 7–14 days of organic substrate, is that the plants will remain healthy, grow with a lush green vibrancy and not go short of nutrients, resulting in deficiencies. Another benefit is the roots will begin to grow upwards through the new top layer as it slowly builds up over time, meaning the final root mass will be greater than without top dressing. 

Top dressing is easy and an excellent amendment for various stages of the growth cycle. It is not an expensive task and investing in bags of different organic materials to use, is easy and practical and will allow you to cover the length of a crop without running low. Below are the examples of different organic substrates that can be used as a top dressing. 

Different Types of Top Dressing for Cannabis Plants

Worm castings: 

These are rich in NPK, and macro nutrients and packed full of beneficial microorganisms. You can either buy a bag of worm hummus from your local garden center and, in some cases, will have worms inside, which is always a good sign. Otherwise, you can always start a worm compost bin at home, feeding them food scraps.


Basically a form of decomposing organic material that consists of leaves and tree bark, that has become active in fungi and bacteria. Compost is also high in Magnesium, making it a great choice for plants that are more heavy on Magnesium, such as OG Kush hybrids. A good batch of compost will have a sweet fungi smell to it and compost bins can be made at home from garden waste such as lawn clippings, leaves and wood bark. 

Lava rock dust: 

You don’t need to add much lava rock dust, to keep the microbes and fungi happy, as well as enduring the growing medium has a high volume of trace elements and macro nutrients leaching back. 

Mycorrhizal and Bacteria inoculant: 

When you buy a complete soil that already contains worm casting, compost and other organic material, then there will be a good level of mycology within the soil. However, if you want to take things to the next level, you can always invest in an inoculant which can be used as top dressing, or inside a liquid compost tea. 


Basically a form of pure carbon that started life as a piece of wood and, through extreme heat, became a compressed block of carbonated wood. What is fascinating about biochar, is that the surface area of a piece the size of a sugar cube, when opened up flat, would consume the size of a football pitch. This being said, biochar has incredible water holding retention, and is a long term source of carbon for the soil food web.

What are Organic Teas?

Now we have covered top dressing as a slow release and hard food supplementation, organic teas are the liquid version and are very easy to make, and allow the plants to quickly access nutrients. There are different methods of making organic teas, ranging from the most basic of cold water extraction, to the more complicated and expensive aerated tea which involves an air pump and air stone. 

Organic compost tea is used all over the world by farmers and is a wonderful way to enrich the earth with beneficial microorganisms that connect the soil food web together as one giant network of bio-intelligence. 

The Difference Between Aerated and Cold Water Extracts

Cold water extracts - These are the easiest teas to make and involve allowing organic matter to sit inside a cloth net and slowly leach into the water source. In some countries, using a bamboo stick over a plastic bucket with a sock or cloth net works perfectly well. Inside the bag will be anything from worm castings, compost, animal waste, guano and whatever is indigenous to that region. 

Aerated compost tea - A step up from the cold water extracts, aerated teas require a bucket, air pump, air stone and 24 hours of brewing time. The science behind an aerated compost tea is that the aerobic beneficial microorganisms and fungi inside will multiply in population from millions into billions thanks to the oxygen present in the water. You will know the tea has brewed well when there is a layer of foam developed over the surface of the water after a full 24 hours. 

Which Are Best for 18/6?

During the vegetative stage of 18/6, it is best to use aerated compost teas made from worm castings and compost, and to avoid anything high in Phosphorus and Potassium until the flowering stage. Using these two organic substrates will allow you to keep a consistent level of nutrients readily available and ensure plant health is at a maximum. 

Which Are Best for 12/12?

Once Cannabis plants have entered the flowering period, they will demand higher amounts of Phosphorus and Potassium in order to develop thick and terpene rich buds. It is a good idea to use different guano that have an NPK ratio of 2-10-2 or 1-10-0, and to combine them with worm castings and compost, to ensure there is an abundance of micro and macro elements at all times.


The great thing about calling yourself an organic grower is how versatile you can be. There is no set way to grow, and everyone has their own preferred methods of feeding. Top dressing is one of the most practical and easy to perform tasks there is, and as long as top dressing is applied every 7–14 days, then you will be well on your way to a happy and healthy crop. Experiment with making your own cold water or aerated teas and try new things out of your comfort zone. Good luck becoming the best grower you can be and taking your organic game to the next level!