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!
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.
Here are some simple instructions for making it.
- Collect weeds and chop them up – smaller pieces decompose faster. You can also use other plant parts like deadheaded flowers and even grass clippings.
- Place the material in a bucket and fill it mostly with water.
- 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?
- 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.
- Wait two weeks. Stir when the urge triggers you to do so – this is a precise process!
- Remove the liquid and use it as fertilizer.
- 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.
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.
Ideas about wood chips are evolving rapidly thanks to research done at Laval University. Branches that are under 3.5 cms contain high levels of nutrients and have a much better carbon to nitrogen ratio than trunk wood. Deciduous wood is preferable because conifers contain chemicals that suppress growth. (except larch, the exception to every rule) You can Google ramial chipped wood to find out more. These ideas have not gone mainstream yet but I can’t imagine why. Organic orchardists are pioneering most of the practical application work on this now.
Do you have a link about the problem with conifers?
The rule of thumb for ramial wood chips is no more than 20% softwood. Everything written on ramial wood will include that information. This specific quote is from the orchardist Michael Phillips:
“The brown rots transform softwood cellulose to produce polyphenols and allelopathic compounds specifically relied upon by evergreen species to suppress deciduous species.”
https://www.groworganicapples.com/organic-orcharding-articles/ramial-wood-chip-primer.php
I had a look at the article on the nutrient content you referenced.
How did you come up with 3-7-4 NPK ratio.
I had a look at you NPK article and I calculated 2-3-6, or more accurately, 27-36-67.
Can you show me you calculations so that I understand clearer.
Thanks
that was a long time ago.
I used to get human sludge from the water reclamation plant decades ago. It worked great..I did have tons of volunteer tomatoes though!
And as for using wood chips as a mulch..it does work great but ti does suck up lots of nitrogen in the process.of breaking down. Like wise I planted a tree over a spot where there used to be a tree. The new one isn’t growing much..arborist told me the roots of the old tree breaking down were robbing the soil of nitrogen…I drill deep holes and put fertilizer down the hole now..I’ve been too inconsistent to tell if it is working.
I already have too much work to do around the place without hassling with weed tea.
“but ti does suck up lots of nitrogen in the process.of breaking down” – only from the very top layer of soil were you don’t find roots.
I found this article very helpful. The NPK quotes numbers are very good flowering plants such as cannabis or regular flowers. I’ve always known the NPK to be for their stages of life. Nitrogen for the beginning and anything green. Phosphorus to increase blossom productivity. And potassium for seeds and stem strength.
Though that being said I also say the teas are very good for potted plants that have the own root system. With the bacteria being a bit fragile to extreme droughts (forgetting to water often) since I’ve been looking more into teas I think they would of done my grannies plants well… she was a good gardener tho forgetful in her old age
I’ve got pear trees that struggled along with fruit tree spikes for years. Fruit set was low, the pears were small and scab was a big problem. A few years ago, I stopped using chemical fertilizers to allow the trees to make mycorrhizal connections with fungi in the soil and started foliar feeding with tea made from seaweed, comfrey, nettles and horsetail as recommended by Michael Phillips in his books.
The results are astonishing. The leaves are noticeably more healthy, there so much fruit set, I have to thin the pears, most pears have no scab at all and the fruit are larger. If organic feeding does nothing. how do you explain this?
You have done several things:
1) change in fertilizer program
2) foliar feeding
3) time – the plants are now more established
There is no way to know which of these or other changes had an effect.
These trees were planted 20 years ago so more established is really not a factor. The use of chemical fertilizers is proven to disrupt fungi in the soil and mycorrhizal fungi is increasingly recognized as one of the best ways to feed plants. There’s also growing emphasis on the use of ramial chipped wood to provide trees with nutrients. Ramial wood depends on white rot, another kind of fungus which is also harmed by chemical fertilizers. Gardens can be self sufficient in nutrients but not if chemical fertilizers are applied. I learned about the importance of avoiding chemical fertilizers to prevent harming natural fungi in the soil from a mycologist at Western University Dr. Greg Thorn.
“use of chemical fertilizers is proven to disrupt fungi” – that is not proven. If you add the same nutrients from either synthetic fertilizer or organic material you will get identical effects.
It’s your word against that of a leading Canadian mycologist who was adamant about the negative impact of synthetic fertilizers on soil fungi. Most people know, if you want to get rid of mushrooms in your lawn, a high nitrogen fertilizer will do the trick.
This idea that synthetic and organic fertilizers are identical does not take recent advances in understanding soil ecology into account.
Lets see some proof. Post a link to a study that shows what you claim.
Lets assume that nitrogen fertilizer stops mushrooms. What happens if you add the same amount of nitrogen in the form of blood meal? I’ll bet it is the nitrogen level that is import – not the “synthetic” part.
“This idea that synthetic and organic fertilizers are identical ” – nobody ever said that. What I said was that the nutrients in both are identical molecules. Organic has another component – which is the carbon component, which is lacking from synthetic fertilizers. They are not the same, but the nutrients in neither is going to harm microbes provided the levels are reasonable.
You didn’t post my last comment? Do yourself a favour and ask Dr. Greg Thorn directly if synthetic fertilizers are harmful to soil ecology.
I did post your last comment – you just need to show some patience.
Agreed.
What may have some effect are a lack of micronutrients, though I’d suggest it would be far more productive to add an annual mulch of well rotted compost rather than spraying plants with “weed tea”.
That way the soil itself is improved on a long term basis.
Weed tea will never have more micronutrients than the weeds themselves. The tea may make it easier to spread them.
The link in the article that has the NPK values also shows some micronutrient levels.
I do apologize for assuming my comment was not going to be published.
You can find older studies that say there’s no impact but the consensus now is that synthetic fertilizers, especially phosphorus, will inhibit mycorrhizal fungi whereas organic material does not. The companies that sell inoculant have this information on their sites. Also, if you purchase soil that’s inoculated, it will be organic.
But let’s return to fermented teas and their use. The purpose of foliar application is not simply to feed the plant, although that works very well. The other purpose is to increase microbial activity on the leaves (and also on the fruit and bark) to such high populations that pathogens cannot find a toehold. The decline of scab infection on my pears is about 80% and not a coincidence. This is the biological action of the fermented teas at work.
“the consensus now is that synthetic fertilizers, especially phosphorus, will inhibit mycorrhizal fungi whereas organic material does not. ” – you will find no such consensus in the scientific community, because phosphate from both sources is identical. What is a consensus is that high levels of phosphate inhibit mycorrhizal fungi.
” if you purchase soil that’s inoculated, it will be organic” – one has nothing to do with the other. You should look up what organic really means.
Weed tea. I have always thought if you compost weeds you get their seeds and they will grow again when you apply compost. I cann tomato/ spaghetti sauce. My machine strips out the skin and seeds and I just get the juice to cook down. The skin and seeds use to go in my composter until I started seeing tomato sprouts in the finished compost. At the end of a compost cycle I would transfer to a plastic trash can with a lid and after a few weeks I would see tomato sprouts. It stops after I let the compost dry out completely. Two years later I’m in a different house and I am getting tomato plants under my fruit trees from 2 year old compost. Did I compost wrong or are tomato seeds that tough?
Great article, as always Robert, thanks.
I put weeds on the compost heap, except the roots of pernicious weeds, Bindweed etc., which go into a bucket of water to drown them (I’m in UK, can’t guarantee Summer weather that will dry them … if I lay them on the grown chances are that the blighters will grow). I’m not making Weed Tea, just trying to kill the weeds. But … I reckon those deep rooted weeds pull up nutrients from deep down (the reason I grow Comfrey for plant feed), so have value in that sense – depending on whether any plants actually accumulate nutrients from down-deep of course, but Bindweed has lots of, deep, fleshy roots so I presume they are “storage”. I chuck the whole bucket on the compost heap after I am sure they are drowned-dead.
But, no seeds. I expect to dig out Bindweed etc. before it gets to the point of seeding, but if I miss any and they have seeds then the tops go off-site / to garbage. I could drown them too, but seeds are more robust and I am not organised enough to remember how long I have steeped and whether long enough.
I hear you. I live in the NW and so I never leave the weeds alone on the ground, just not hot enough to kill them. They resprout readily in many cases. I do however throw them in the compost heap if they aren’t runners, and as long as they haven’t flowered. They will go to seed if left on the plant. Flower parts go in the trash. Great post!
I put everything in my compost bays, even stuff like bindweed, ground elder & twitch grass roots. I just make sure they go in the middle, where the temperature stays at 60°C/140°F for several weeks (along with fish & fowl bones, rat carcases, rabbit trimmings…).
“Recycled beer” is by far the best thing to use for keeping the bays moist & after all, once I’ve drunk it, there’s no other use for it…
As for weed teas: Nah, put a good inch or two of well matured compost on ther surface of your beds each year & there’s no need for any other supplementary feed, even with three crops from the same bed.
If weed tea stinks as you say Robert, it might be a good idea for me to start making it and storing it by the fence to stink it out my neighbours who deliberately sit the other side chain smoking tobacco / cigarettes, the smoke continually drifts over to myside, and turns what should be a pleasant gardening experience into an antisocial carcinogenic nightmare. Perhaps the stink would cause them to go elsewhere!
Hello! I have four big compost bays. What do you think about adding not just rthe spent weeds but the liquid to compost as it breaks down? I thought it might be working as a starter, but that might be wishful thinking. Would avoid having to think about NPK perhaps?
It is organic material and will break down.
Hi, Robert. Thanks for getting back so quickly. I wasn’t clear. I was talking about adding drowned weeds to the compost along with the compost tea, and I wondered whether they would act as compost accelerators? We have loads of what kgarden beautifully terms pernicious weeds that would LOVE to be added direct to the compost heap where they’d thrive!
So would either part of the process, liquid or solid, act as an accelerator? Tradescantia is the weed we have most of. Not as good I’m sure as comfrey, but does it, once broken down, have food value for the garden?
Depends on why you need to accelerate things. If your C:N ratio is too high, then greens will accelerate compost.
You can add pernicious weeds to fermented teas. Some are better than others but all will absolutely die. Horsetail (Equisetum) contains high levels of silica, and so do nettles just before they set seed. When these plants are put into a fermented tea and sprayed directly on developing fruit, the silica creates a protective barrier that helps the fruit fight off fungal pathogens.
If you want an intelligent discussion about the uses of fermented teas in organic gardening, you can do no better than Michael Phillips. HIs book Holistic Orchard won the American Horticultural Society Book Award.
Humani-tea is better – dilute human urine at least 1/5 and use it to water plants that look like they could benefit from some N (yellowish leaves). Weeds can just be chopped up by a lawn mower and used for mulch. I am plopping something like this weed-tea mixture, soaked mower-chopped vegetation with about an equal amount of soil, on runners of our Cucurbita moschata Squash, so they can get roots into the soil away from the place they were planted.
Hello Fred, you are a man after my own heart.
I’ve been championing the use of human urine from the rooftops, its such a waste to flush it down the lavatory. Use as fresh as possible ie as soon as possible, if you are not going to use it straight away keep it covered to retain the nitrogen, which can be lost to the air.
I personally dilute to around 1 part human urine to 9 parts water, if I am going to water plants with it. Other than that I I fill a bin with autumn fall leaves and cover them with neat urine, no it does NOT stink, don’t ask me why, but I can honestly say it doesn’t smell.
When I read your word “plopping” I wondered what you were going to come out with next Fred 🙂
Jo: with regard to “such a waste to flush it down the lavatory,” the wife has developed the theory that it’s inappropriate to “go” into water, so we deploy the urine to gardens and plant communities that benefit from increased nutrient levels, and run a dry outhouse with wood ashes for the “plops,” so that none of our contributions go to waste.