How And When to Apply Compost Tea….and How Much

Once you’ve brewed a batch of high biology compost tea as discussed in our blog post titled “Compost Tea Brewing Like A Pro“, you’re ready to get that good biology onto soils and plants.

In this article we’ll touch on small thru large-scale application methods, and how and when to apply compost tea for the best results! We’ll also talk about dilution rates to pump the most biology over the greatest surface area.

General Applications

Compost tea is great for any plant, large or small.

Turfs , vegetables, flowers, and trees can all benefit from this liquid elixir. Compost tea is an inoculant, treating plants and soil with beneficial microorganisms.


Anything that is used to water plants or apply liquid fertilizers can be used for compost tea.

Small vegetable or flower gardens can be handled with a simple watering can. Handheld or backpack sprayers also work well for applying compost tea on a small scale.

Pro Tip! Remove any inline filters that may be found in the wand of the sprayer so they don’t get blocked up with sediment.

Medium and Large-Scale

Medium-scale operations can use a spray tank with a boom on an ATV or small tractor.

Larger farms can adapt existing spray equipment such as booms with spray nozzles to work with compost tea. Ingenious farmers can rig just about anything to apply compost tea on any scale.

A Note On Nozzle Size

Nozzle openings need to be at least 400 micrometers or greater when using any type of drip emitter or sprayer. If you can see through the nozzle hole, then it is large enough. We are working with tiny organisms that need to be viewed with a microscope.

Common sense tells us that if you can see through the hole, microorganisms can definitely pass through unharmed.

Spray Rigs

Commercial spray rigs are available for sale through various sources.

Some are sold exclusively as compost tea spray units like what is available from Green Pro Solutions. Commercial lawn equipment dealers usually carry a 100-300 gallon spray rig that is meant to spray lawn chemicals but can be used for compost tea.

I made my own compost tea spray rig out of an IBC tote and a water pump.

I capped off the original hole that is meant to empty the IBC tote and installed a bulkhead on the opposite side. A heavy-duty hose with quick-connect couplers for easy on and off attaches the tote to a Honda water pump. Off of the pump runs 200 feet of heavy rubber garden hose. I use a spray gun with an adjustable nozzle that goes from mist to stream, and also use a root injector to apply compost tea to the root zones of trees.

Pumps and Sprayers

Applying compost tea on any scale will involve some type of pump and sprayer.

When choosing a pump, whether small or large, it is best to use a diaphragm pump as they will cause the least harm to the microbes in compost tea. Diaphragm pumps tend to call for a higher price than their counterparts although not considerably more.

Backpack sprayers with diaphragm pumps will be easier on microbes than the more commonly sold ones with piston pumps. But you’ll be fine if you want to use a piston pump if that’s all you have.

Larger sprayers come with either a diaphragm, roller, or centrifugal pump. Roller pumps have been found to be the hardest on microbes in compost tea. Second to that is centrifugal pumps.

Diaphragm pumps work similar to bellows that are used for adding air to fires. They create a vacuum to pull liquid in one side and push it out the other end.

This gentle action makes them the best choice for using with compost tea sprayers.

Keep The Microbes In Mind

I recommend against running the pump while the sprayer is not in use.

Running a pump without the release of compost tea through the sprayer results in the liquid is being sloshed around within the pump. This can be detrimental to the biology.

So turn the pump off for any excessive time that the sprayers are not spraying.

The strength with which compost tea gets blasted out of a spray gun can be an issue for microorganisms.

Using a microscope to look at compost tea both before and after running it through a sprayer is the only true way to check for any disturbances. Keep the pressure dialed back as much as possible on the sprayer output to avoid harming microorganisms.

How To Apply Compost Tea

Compost tea provides microorganisms to soils, soilless mediums, and hydroponic systems that work to cycle nutrients to plants naturally. It is essential to apply compost tea to the root zone of plants. For lawns and landscapes that could mean applying compost tea to the surface and allowing it to soak into the roots. Seeds and starts can be dipped in compost tea when initially planting a lawn or garden.

Foliar Coverage

Apply compost tea to the foliage of plants as well as performing a soil soak around the root zone. Microbes help to form a sheath around plants to ward off pathogens and diseases.

Aim at covering at least 75% of the foliage with compost tea.

“Water the Root To Enjoy The Fruit”

Root injectors, as mentioned earlier, work to get compost tea down into the rhizosphere, or root zones, of larger plants and trees. It consists of a metal probe with a point on the bottom end.

Holes in the pointed end allow for liquid to stream out. The top end has a handle with a trigger that connects to a hose.

Rates of Application

Spraying Compost Tea

Five gallons of compost tea per acre, for every five feet of height in foliage, is the lowest rate of application.

For example, the application rate for an orchard with 10 feet tall trees would be 10 gallons per acre.

20 feet tall trees, 20 gallons per acre. At Rodale Institute we used five gallons of per acre for research purposes and got noticeable results.

Compost tea is so inexpensive to make that I generally use a rate of 10-20 gallons per acre.

Root Injections

Root injections call for even more compost tea. I aim at getting three to five gallons of compost tea into the root zones of saplings up to about eight feet tall which have smaller trunks.

I will go with 10 gals for medium sized trees that have trunks two to four feet in diameter, 20 gallons for larger trees.

Be sure to spray the foliage of the trees too!


You will likely need to dilute compost tea in water in order to use a rate of five to 20 gallons per acre of land, so that it will spread the solution farther.

Imagine holding five or 20 gallon jugs full of liquid and having to get that out over 44,000 square feet of area.

It’s not possible.

So how much should you dilute compost tea? You can dilute compost tea however much you need for your application.

Let’s say you have six small, raised-bed gardens and know it takes 12 full watering cans to cover the area of these beds. Dilute the compost tea down amongst the 12 full watering cans and apply.

If it takes a full 200-gallon tank to cover two acres of pasture land, dilute 20 gallons of compost tea into 180 gallons of water. Water mainly acts as a carrier to get compost tea out over a sizeable area. It is difficult to dilute compost tea down too much.

However, booms with spray nozzles generally work efficiently enough that dilution may not be necessary.

Microbes Need Water

Whether I’m spraying a lawn, landscape, garden, or farm, I take much more water than I think I need.

The microorganisms that we are working with need water to survive and to continue to repopulate. They live in the microdroplets of water in soils. This is why mulching is so important as it keeps garden soils moist.

Picture the soil profile as a sponge.

When a sponge is dry, it’s hard to penetrate the surface with liquid. When a sponge is wet, any liquid added to the surface gets drawn into the sponge more easily.

In this same sense, adding extra water to the compost tea will help to drive these microorganisms deeper into the soil.

The excess moisture will allow for a healthy, bustling population of microbes to continue.

Adding Food For Microbes After Dilution

On an average day of spraying compost tea I fill my tank with 250 gallons of water and add 30 gallons of compost tea. That is a rather large water-to-compost tea ratio. As a result, I like to add foods for microorganisms to my dilution water.

There are no set guidelines for the amount of microbial foods to add.

But my personal rule of thumb is to I add one to one and a half cups of humic acid and the same amount of fish hydrolysate to 250 gallons of water.

Larger quantities of foods can be added but it becomes harder to clean the insides of the spray tank, which is difficult task enough already!

Compost Tea Supplements

Mycorrhizal Spores

Mycorrhiza is a symbiotic association of the mycelium of a fungus with the roots of a seed plant. Hyphae from mycorrhizal fungi are directly connected to either the exterior or interior of a plant’s root cells. Through photosynthesis, plants produce excess carbohydrates. They feed the surplus sugars to the fungi through their roots. In return, mycorrhizal fungi provide plants with water, nutrients, and minerals that they mine from the soil.

Mycorrhizae are able to transfer these substances back through their own cells all the way to the plant’s roots.

As a result, plants are able to obtain water, nutrients, and minerals from much farther distances than they could on their own. Other benefits of mycorrhizal fungi include improved soil structure, faster root development, and increased stress tolerance.

If there is one practice that people don’t make use of enough, it is adding mycorrhizae when planting seeds or starts.

Mycorrhizal spores can be purchased and used in a granular or soluble form. The soluble form makes a great addition to mix into a compost tea brew. Be sure to add spores after the brew process as they will otherwise get mixed in with sediment.

I add them to the spray tank and mix them into the diluted solution.

Rock Out with Some Azomite

Azomite which can be purchased on Amazon

I also like to mix some Azomite into the spray tank solution.

Azomite is a rock dust derived from an ancient volcanic eruption into a seabed that is mined only in the state of Utah. It’s full of trace minerals and micronutrients that plants use.

The microbes from compost tea will help to make these trace minerals available to plants.

Frequently Asked Question: What About Rain and Compost Tea?

I often get questions about spraying compost tea when rain is in the forecast.

The same thinking as dilution can be applied to rainfall and compost tea applications; water will benefit the microbes.

I don’t like to spray compost tea during a heavy rainfall as it may wash the compost tea and microorganisms off of the foliage. A light rain or mist shouldn’t have much effect.

Spraying compost tea after a rain event will help to pull the compost tea and biology into the soil profile as the rain draws deeper into the earth. A rain event after applying compost tea will help to push the compost tea into the soil. All of these microbes will be spread further into the soil by the water from rainfall.

When To Apply To Plants

Seed Starting

Introduce beneficial biology as early as possible for the greatest advantage.

Plant life starts with a seed or bulb.

Seeds and bulbs can be soaked in compost tea to get them inoculated with microorganisms as well as hormones that help promote germination and root development. It doesn’t take much, even a quick dip, to get some biology onto the seeds.

Boost a Plant’s Microbiome Early On

While seeds do contain all they need to begin life and grow, beneficial biology will give them a much healthier start in life. Human babies are no different. They come out of the womb ready to grow and develop. However, studies show that babies born vaginally both ingest and are coated with bacteria from the mother’s microbiota.

These microorganisms help to greatly boost the immune system of the child as well as aiding their digestive capabilities among other functions.

Plants are similar to humans in this manner.

Seeds and seedlings provided with beneficial microbes have healthier immune responses, better metabolic functions, and generally outperform un-inoculated plants.

Prior to Planting

I soaked some seed garlic cloves for 20-30 minutes prior to planting last December. When taking off in the fall/winter, this particular garlic variety usually sprouts 4-6 roots. While applying mulch a couple of weeks after planting, a garlic clove popped up out of the soil. I grabbed it and counted close to 30 roots that were about an inch and a half long!!

How’s that for soil biology?

So a tea application prior to planting may supercharge your results!

Seedling Stage and Beyond

The next best times to apply compost tea are at the sign of the first true leaf, then one and two months later.

You really can’t overdo it with compost tea.

A bi-weekly or monthly application would benefit any plant, but most growers will not have the time when tending to other farm duties.

Microorganisms in compost tea work like the microbiome in humans. Bacteria and fungi help to keep us healthy, digest our food, and make nutrients available for us to use. Therefore, keep beneficial biology associated with plants from a young age.

The better start a plant gets in life, the better it will develop and perform.

During Periods of Vulnerability: Give ‘Em Some T(ea)LC!

Plants such as tomatoes and roses are especially susceptible to fungal diseases that drift with the winds in the muggy, hot summer months.

Keep these types of plants protected by applying compost tea to the foliage once a week or once every other week. Microbes in compost tea will work to provide a shield against these harmful organisms which can weaken and destroy a plant’s health.

After An Outbreak or Attack

Compost tea adds helpful microorganisms to plants after a problematic outbreak. In the case of a sudden pest or disease outbreak it’s best to first use an all natural pesticide, fungicide, or bactericide. Choose one that is the least harmful to any life forms.

Better yet, choose a biological control if possible.

After the disease or pest issue has been taken care of, go back within a few days to give an application of compost tea and coat the plant’s foliage with additional microbes.

Compost Tea: Safe For Kids & Pets

Compost tea lets kids be kids.

Kids and pets can actually play in the yard while compost tea is being applied. Chemical fertilizer companies recommend that kids wait at least “24 hours after rainfall or irrigation has watered in the fertilizer”. Kids and pets are meant to play outside, not be banned from the lawn.

Chemical fertilizers can poison pets and people if ingested or inhaled.

If you’re somehow in the habit of eating grass, compost tea may taste bad, but it will add to your gut flora.

True Story: Safe to Drink Too!

I was set up at an urban garden festival when a tomato farmer stopped by my table. He was excited about my compost tea and I offered to trade a gallon for some of his tomatoes, figuring a farmer knows about compost tea.

He took his gallon of compost tea and I was to stop by his table in a while to get tomatoes.

A couple hours later I was at his table to pick up tomatoes and noticed that the gallon of compost tea had some missing. I couldn’t help but ask if they drank some and after a quick glance at his daughter he responded with a yes. After explaining that compost tea is for plants not people he smiled and said “Well it did taste like s*@t”. . .

As far as I know, that man is still alive.

Wrapping It Up: It’s Always Tea Time

For those of you who indulge in the occasional adult beverage, you’ve heard the saying “It’s 5 o’clock somewhere, meaning it’s always time for a beer.

Well every hour is happy hour for compost tea. However – and whenever! – you apply it is likely to inject your plants and soil with beneficial biology.

Make microorganisms your friend, work with nature, and promote life of any size when you choose compost tea. Start incorporating soil biology with your plants to get longer-lasting blooms, more nutrient dense produce, and a truly “green” lawn.

Anytime is tea time when you have a garden, farm, or lawn.

If you want to know if your soil is appropriate for your crop, or if you need help our help with anything else, engage our services today!

7 thoughts on “How And When to Apply Compost Tea….and How Much

  1. Another great article Troy. Thank you for your dedication to the soil food web and worm farming communities. Keep em comin’!

  2. Hey Troy;

    The other day I brewed up some tea for a customer. He had some questions about the safety of the tea and could it harm people or pets. Just as a demonstration, I took a big gulp of the Tea. Aside from the gritiness of the tea, it wasn’t bad. I’m thinking with a little filtration and maybe some sweetner etc plus a little carbonation, an enterprising individual could create the next “Cola” sensation.

    1. Some people DO consume humates/ humic acid to improve their gut health. Maybe restaurant servers will soon be saying “…Iced tea, sweet tea, or compost tea” when listing drinks. = D

  3. I was going to try a molasses-liquid calcium mix on 14 ac as a weed control project, but the cost is prohibitive. Thinking now of making a compost tea and using it instead. Is this idea practical do you think? Thanks

  4. When I’m foliar feeding the plants compost tea should I use a bit of dish soap? I want the tea to adhere to the leaves but don’t know if dish soap (natural, Mrs. Myers) hurts the microbes?

  5. Great info. I’m a beginner and trying to learn. I’m making a brewer out of 275 gallon tote. My question: when I empty 200 gallons into my sprayer to put on my pasture, can I immediately refill the brewer with water and start the process over again?

    1. Hi Richard,
      I would probably be cleaning out the brewer to prevent biofilm from forming on the walls and inside the tubing. This would be even more important for aerated teas that use a food source like kelp meal or molasses. Maybe less important for extracts that don’t use those food sources.

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