Weed Tea, Fertilizer Tea – No Matter the Name, It Stinks

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Robert Pavlis

I read about weed tea many years ago and I made some. It stunk so bad that I never made it again.

With all the interest in natural gardening it is making a comeback and the internet is full of gardening advice that says fertilizer tea made from weeds is great for plants. Let’s have a look at the science behind this gardening practice. Is it worth making weed tea fertilizer? What kind of nutrients does it really provide? Are there better ways to use your weeds?

Just to be clear – I am talking about the weeds you pull from the garden – not the kind you smoke!

Weed Tea, Fertilizer Tea, No Matter the Name It Stinks
Weed Tea, Fertilizer Tea, No Matter the Name It Stinks, source: permaculture news 

What is Weed Tea Fertilizer?

Weed tea fertilizer is made by adding weeds to water and letting them ferment/decompose for a while. The resulting juice is the weed tea.

Plant Science for Gardeners by Robert Pavlis

Here are some simple instructions for making it.

  1. Collect weeds and chop them up – smaller pieces decompose faster. You can also use other plant parts like deadheaded flowers and even grass clippings.
  2. Place the material in a bucket and fill it mostly with water.
  3. Some people cover it to keep out flies, but I think added fly eggs and larvae can only improve the quality of the tea. I doubt mosquitoes will lay their eggs in this stuff?
  4. Some people keep the pail in the shade, others in sun. The warmth of the sun should speed up the process and make a better tea.
  5. Wait two weeks. Stir when the urge triggers you to do so – this is a precise process!
  6. Remove the liquid and use it as fertilizer.
  7. Don’t store too long, it might rot out the bottom of the pail.

After only two weeks, most of the weeds will still be there; what do you do with the left over weeds? You can add them to the garden or compost pile.

WARNING: This stuff stinks!

Weed Tea vs Compost Tea

Weed tea and compost tea are prepared in similar ways, but they start with different raw materials; one uses manure or compost, the other uncomposted plant material. Some compost tea is made aerobically, with the addition of air.

My previous reviews of compost tea have shown that, in normal garden environments, the tea has no additional value over and above the compost. There is almost no scientific testing of weed tea, but I am sure the same can be said about it.

Both provide two things; nutrients and microbes.

Brewing a tea will not increase the total amount of nutrients available.  It might speed up decomposition and therefore cause nutrients to be released faster from the organic material, but the total amount does not increase.

There is very little support for the benefits of the microbes in such teas. The reason is that garden soil is already saturated with microbes. Adding more does not increase or change the existing populations. There are some specific cases for disease control, but these are best left to agriculture and not gardens.

YouTube video

Using Weed Tea Fertilizer

Here is one problem with this method. Gardeners don’t know the NPK of their finished product. So, they don’t know how much to give to plants. Using this stuff is all a guess, but that does not prevent lots of self-proclaimed experts from telling you how much to use. Here is what some say.

Use it straight. Dilute it 50% with water. Dilute it 1:10 with water. You see my point; nobody really knows. All these “so-called experts” are just guessing.

You can use it in potted plants, containers, raised beds, or even as a foliar spray. Lots of online advice suggest foliar spraying is best because “leaves absorb nutrients faster than roots” making it more efficient. That is not really true, except for some micronutrients, and unless you are trying to solve a specific nutrient deficiency, adding it to soil is better.

Which Weed is Best?

Some people claim one weed is better than another. Some use grass because it has high nitrogen. Others swear by comfrey because it is a “dynamic accumulator” – it’s not.

I am sure some plants are better than others, but I have found not scientific evidence that one makes a significantly better tea than another. Since most of the nutrients are still in the plant and not in the tea, at the end of the process, I doubt it matters too much. Cutting up the plant, or mashing it up, probably has a bigger affect on the nutrient content.

Soft tissue will decompose faster than hard tissue, so soft leaves are better than hard rubbery ones. Green, fresh stems are better than older hard stems.

Use what you have and the more you use, the better the weed tea.

NPK of Weed Tea Fertilizer

You can find hundreds of online sites that tell you how to make the tea. None of the ones I looked at, told you the NPK of the tea. The NPK is the important part. Would you buy fertilizer without the NPK value on the container? Why make tea without knowing the NPK?

I only found one scientific study that made weed tea and tested the NPK. They tested water hyacinth (Eichhornia Crassipes), Russian comfrey (Symphytum officinale) and pig weed (Amaranthus retroflexus) plants. Each one produced about the same NPK value with the average being, 3-7-4.

Note that they incubated the weeds for 30 days, not just 2 weeks. You can expect to have lower values after 2 weeks.

A good nitrogen fertilizer level for plants is 150 ppm which is 0.015%. A 1:10 dilution of the above weed tea would give you a value of 0.3%.

The weed tea fertilizer contains a good level of nitrogen and would be a good way to fertilize potted plants and containers. You would need a significant amount of liquid to do a garden.

A good general NPK value for plants is a ratio of 3-1-2, so the phosphate level of weed tea is on the high side.

Best Way to Use Weeds

What is the best way to use weeds?

I see many people saying that they throw them in the garbage. That is just a waste. Even weeds that spread easily from runners can be dried a few days in the sun and added as a mulch on gardens without any problem, especially if placed on top of wood chips. This is the method I use – the cut and drop method.

Almost all weeds can be composted.

Making tea does NOT increase the amount of nutrients over and above these other methods for using weeds.

Making weed tea seems like a complicated process that takes extra time and space. Even when you have the tea, you still have to go around the garden and dispense it to plants. It might be a convenient way to fertilize containers.

Warning, don’t make it near the neighbor’s fence – did I mention – it stinks.

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

51 thoughts on “Weed Tea, Fertilizer Tea – No Matter the Name, It Stinks”

  1. Is it OK to put an air tight lid on the weed and water bucket to contain the smell? Or does it need aereation? I had my basement windows open and the smell got in my basement. So I put a lid on the bucket and a fan in my basement. The smell is gone but I just need to know if that is an OK thing to do.

    Reply
    • Without air it is not aerobic. Proponents of weed tea would say don’t use a lid, but since weed tea does not really do much in the garden – it does not really matter.

      Reply
      • Robert, you are never going to accept the fact that anything but chemical fertilizers work. Farmers literally pay hundreds of thousands every year for this stuff, making their operations borderline profits. In the meantime, there’s a whole movement of regenerative agriculture that’s moving away from this type of farming completely. Read the recently published book Soil to Dirt, One Family’s Journey into Regenerative Agriculture by Gabe Brown. It’s entirely possible to run a large, successful operation without using any kind of chemical fertilizers. Farmers all over North America are doing this now. The costs are as much a motivating factor as the need to conserve soil.

        Reply
        • “you are never going to accept the fact that anything but chemical fertilizers work” – then you have not read much of my work.

          So where is your scientific proof that my comments are wrong? Just because someone wrote a book and said stuff does not make it right.

          I don’t use chemical fertilizers in my 6 acre garden.

          Reply
          • Well, it’s great that you don’t use chemical fertilizer on your land. We know for a fact that plants take in very little of the chemical fertilizer that’s applied and runoff caused by mechanical tillage that compacts the land creates serious problems in waterways with algae that sops up the excess nutrients. The book I referred to has plenty of references to scientific work that supports regenerative agriculture as an affordable, sustainable system for larger operations like ranches and farms and hard scientific data about the harm that chemical fertilizers do on the same type of operations. That’s why I referred to it. Chemical fertilizers are in the same category as fossil fuel. The harms are well documented and we need to stop using them. Unlike fossil fuel, the alternatives are cheap and already at hand.

          • Chemical fertilizers are not nearly as harmful to soil as claimed by many.

            Given our current population, we could never grow enough food to support them without chemical fertilizer. The idea of regenerative methods is great on a small scale, but not realistic to feed the world.

          • Robert’s point about these teas is that if they’re going to fertilize nutrient-deprived plants, they’ve got to contain the NPK that the plants require, and many of these vegetable tease recipes just don’t provide the nutrients. We make a vibrant yellow tea with our kidneys, which we dilute to promote rambunctious growth in all our vegetables, but it’s well known to include urea and other nutrient chemicals….

        • Robert has pointed out the positives of using compost for many years.
          I’ve just watched the farm next door spreading last winter’s slurry on their grazing land after a second cut of hay – no artificial fertilisers there. He usually grows a few acres of root vegetables & brassicas for local sale & they never see artificial fertilisers but they do see chemical pest control, so it’s not due to any desire to be ‘organic’.
          He doesn’t use ‘weed tea’ as adding well rotted organic matter to the soil is far more effective & efficient.
          I’m not going to faff around with weed teas when an annual application of 3cm of compost keeps my no dig beds healthy & productive with little effort.

          Reply
    • I am missing the point?

      Organic material contains nutrients. If you add them to soil it provides nutrients for plants. No mystery here.

      Reply
      • Between your write up here and your youtube video on this subject it appeared there was a dearth of any kind of data or testing on grass tea/weed tea. I dug, asked around, and ultimately came across that — there isn’t much else.

        it appears to show, barring methodogical error, or fabrication or something like that, that their grass tea yielded a fairly useful concentration of NPK, with a 50% dilution resulting in the target ~150ppm of N in particular..

        There is of course no mystery around organic materials containing nutrients. The question pertains to liquid extraction and viability/lack thereof.

        In a youtube reply to a comment about more rigorous NPK testing you stated : “I would like to see them done in a lab too – but science does not test weed tea because they already know it does not work.”

        So I am getting some mixed messaging here — perhaps I am missing the point. I was simply curious what you thought of those results or perhaps might catch a methodological error or something along those lines. I only care about the data and am not a grass tea or JADAM cultist.

        Regards.

        Reply
        • Not sure of the question. There is very little testing of teas. One of the reasons is that no one will pay for such testing, since making compost tea or grass tea is never going to be a valuable commercial product and that is what drives a lot of research.

          Reply
          • There are detailed analyses of the nutrients in different kinds of plant, bone and shell extracts in the 2020 book The Regenerative Grower’s Guide to Garden Amendment by Nigel Palmer so that information now exists. When the war in Ukraine started, farmers were in serious trouble because they depend on fertilizers that are imported long distances, which are not only an expensive, but whave a big carbon footprint and a supply chain that was more fragile than we suspected. The idea of regenerative growing is that most of what we need to feed crops can be found in the land around them. I wish more people would experiment, not randomly but using the growing body of books about this approach because the results speak for themselves. My plant glow after I feed them.

          • “My plant glow after I feed them”
            I don’t know how you measured the amount of “glow”, but yes, plants grow ehen you give them fertilizer.

          • There doesn’t seem to be a way to reply to your last comment. If it’s possible to post a photo, you can see what one of my pear tree’s fruit and leaves look like after foliar feeding. Visitors comment on it.

  2. Great info.
    Would ordinary weed tea from many months of steeping, dandelions, chickweed, oxalis (common lawn weeds), brambles, and rose prunings, sustain captive mushrooms in a container?

    Reply

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