Making liquid fertiliser from weeds is a great way to re-use those pesky plants that grow where they’re not wanted.
As the days grow longer, the plants in our gardens send up new green shoots and flower buds. A delight to the eyes. Less delightful are the weeds that also push up through the soil.
Gardeners are rightly reluctant to throw the roots and stems of perennial weeds onto the compost heap. Many of these plants have the ability to propagate from just a small section of stem, and the nutrient rich atmosphere of a healthy compost bin would offer perfect growing conditions!
However the tops of perennial weeds – the leaves, flowers and – usually but not always – the stems can be twisted off and composted. The roots and stems can often be put in a hot composter, but you may feel it safer to throw them into the council green waste bin or take to your local recycling centre, where the really hot temperatures will make safe composted material.
But the benefits of those composted weeds will take possibly months to benefit your garden plants. And in spring, when so much new growth is bursting forth, it would be good to have a quicker benefit. Which is where making liquid fertiliser from weeds takes centre stage.
By turning those weeds to your advantage you can –
- Save money, as you won’t need to buy any / as much liquid fertiliser
- Grow healthy crops and ornamental plants
- Improve the quality of your home made compost
- Help keep / make your gardening environmentally friendly by keeping it very local
- Offer food sources for pollinators by allowing the weeds to grow in a less used area of your garden and harvesting them throughout much of the year
Which weeds are good to use as liquid fertiliser?
The perennial weeds are the ones to focus on, at least in the first instance, as they have either a tap root or spreading root system which has stored up starch and nutrients over winter. And they produce lush foliage which is also full of goodies for your ‘more important’ garden plants. I’ve picked out the four you’re most likely to have, two with tap roots and two with spreading root systems.
We’ll have a quick look at these weeds and why they’re useful, and then give you the method for making liquid fertiliser from weeds rather than throwing away those useful minerals and nutrients.
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Perennial weeds with tap roots
Those tap roots, go deep into the soil – as you will have discovered when you come to pull them out and a piece gets left behind!
Because of this, they are sometimes referred to as dynamic accumulators. Broadly this definition means that the tap roots draw up nutrients from far below the soil surface. However it’s not that simple: for example, plants can’t extract nutrients if they’re not in the soi to begin with. This is a topic I’ll come back to in another blog as it is worth considering the research and empirical evidence.
For our purposes here, what is important is that those tap roots are a storage organ that allows the plant to survive underground through the winter. As gardeners, we can utilise those stored nutrients and minerals for plants that are important to us.
Dandelions and green alkanet variously contain nitrogen, phosphorus, potassium, magnesium, boron, copper, manganese, sulphur, calcium, iron and silicon. Plus vitamins A and C.
Dandelion, Taraxacum officinale
Although considered a weed when found in most gardens, the dandelion has a long history as a medicinal and culinary herb. For example, you could make wine from the petals, tea and salads from the leaves; coffee and soup from the roots. The dandelion flowers are excellent pollinator plants, especially for bees, as they’re blooming from early spring,
The dandelion flower is made up of lots of smaller florets, all of which go to make the impressive spherical ‘dandelion clock’ or seed head. The individual seeds blow on the wind and generally carry the same DNA as their parent, as most dandelions reproduce asexually.
They create a liquid plant feed that is rich in potassium, which is great for fruiting plants in particular. And dandelion leaves have vitamin A than spinach!
Green Alkanet, Pentaglottis sempervirens
Pentaglottis sempervirens, green alkanet, is a native of South Western Europe and seems to have been introduced in to Britain before 1700, probably during the Middle Ages. Like Dyers Bugloss, Alkanna tinctoria, for which it is frequently mistaken, green alkanet has roots which can be used to produce a red dye, although it is not as strong.
The stems and leaves are covered with hairs which are a skin irritant, so care should be taken when pulling up this weed. Green alkanet does have pretty blue flowers very similar to Borage flowers. This is probably why it has spread so easily, as it may have been mistaken for the prettier, edible plant.
But the nectar-rich flowers are attractive to bees, hoverflies and butterflies, and its leaves are food for the larvae of the exotic-looking scarlet tiger moth.
Perennial weeds with a network of spreading roots
Spreading root systems are as good as tap roots for storing nutrients and minerals over winter. It is after all a survival technique used by lots of plants, not just ‘weeds’. And these two may also be referred to as dynamic accumulators, their roots can spread down as well as along. And again like tap roots, the plant is able to regrow from just a small section of root, making it difficult to eradicate from the garden.
Nettle, Urtica dioica
The perennial stinging nettle is high in nitrogen, calcium, iron, phosphorus, potassium, boron, iron, zinc, selenium, and magnesium, plus vitamins A, B, and C. Which makes it one of the best well-balanced fertilisers that can be used for a wide range of plants.
It is also a natural insect repellent, and when sprayed on leaves can help plants resist insect and fungal attacks.
Nettles cut in the spring have the highest nutrient content and are especially nitrogen rich. So making liquid fertiliser with young spring nettles is particularly good for boosting leafy growth. Plus the flowers are loved by pollinators, and we humans can eat all parts of the plant – why do we think of it as weed? (see blog link below for more on nettles)
Ground elder, Aegopodium podagraria
Actually, ground elder doesn’t have spreading roots as what we see when we dig are underground stems called rhizomes. Be that as it may, the spreading roots and the leaves are a source of minerals and nutrients including nitrogen, iron, phosphorus, potassium plus vitamins A and C.
Ground elder was brought over by the Romans as a food staple, and progressively spread throughout the British Isles. However the modern day gardener spends fruitless hours attempting to get rid of it as unwanted weed. Making use of it as both a fertiliser and a food item seems a more productive result from all that bending and digging than just chucking it into the green waste bin. (Or is that just me?)
What is a Liquid Fertiliser ?
Liquid fertiliser, also known as fertiliser tea, or sometimes weed tea, is made from fresh plant material. This is different to compost tea, which is a liquid made from composted material.
The solution you’ll create from the rotting greens and roots will be a leachate. In this circumstance, it means a liquid which has extracted the soluble material, the nutrients, from the weeds.
It has a short ‘shelf life’, so aim to use it within about a month. By which time, you should have another batch ready, and given the nature of the plants above, you can probably keep this routine up all through the growing season.
Remember this is not a drinkable brew for humans!
Making Liquid Fertiliser from Weeds – How to make it
This is just one, simple method. Fairly fool proof though. Although I’ve named particular weeds above, there are many other plants and weeds form your garden which are suitable. More on these another time.
- Use a bucket or container with a lid to put your weeds into
- But it shouldn’t be air tight as the fermentation process releases carbon dioxide. Which could blow the lid off – you don’t want an exploding bucket of smelly liquid fertiliser…
- Pack the weeds down as tight as possible
- It’s fine to use a mix of root, stem and leaf – in fact this gives you a good balance of nutrients and minerals
- Continue filling until the bucket is around two-thirds full of tightly packed weeds
- Adding a preservative-free fermented food such as yoghurt will speed up the process, but isn’t essential
- Top up the bucket with rain water, NOT tap water because of the chlorine etc
- Leave the weeds to ferment in the bucket of tea somewhere warm for a week or two
- I tend to check progress about once a week. In cooler weather it may take slightly over two weeks, in summer it may only take a week.
Making Liquid Fertiliser from Weeds – How to use it
Before using, it is an idea to strain the weed fertiliser tea through a piece of cloth. This ensures you don’t disperse weed seeds or clog the nozzle of the watering can with bits of rotted weed.
Water-soluble homemade fertilizers are short acting rather than slow release. They should be applied no more than every two weeks, usually as a thorough soaking.
The solution can be strong, so it is advisable to dilute it as you would a shop bought liquid fertiliser. The ratio 1:10 is a good one to start with. Due to the differing content of weeds and nutrients in each ‘batch’ of weed tea, it’s not possible to be definitive, so err on the side of caution. The colour should be similar to a weak black tea.
Where to use it
- Bedding plants – as they put on a lot of growth over a short season
- Container plants – they’re totally dependent on us gardeners for food and water
- Vegetable plot – regularly during the growing season, although not immediately before harvest: then it should be water only
- Seedlings in nutrient poor growing media may benefit from a ‘drink’ before being transplanted to a richer soil. NB Dilute the liquid fertiliser further when using it on seedlings.
- Ornamental shrubs – particularly as the buds are setting and when the shrub is in full bloom
- Herbaceous perennials – as they start to emerge with leafy growth. I also feed if they’re in bloom for a long time
- Shrubs and other perennials – if I intend to take lots of cuttings from a plant I give it a feed 2-3 weeks beforehand
A word of warning – avoid spilling any weed fertiliser tea on your hands or clothing. It smells horrible and the smell lingers!
Uses for Weeds – What else?
By making liquid fertiliser from weeds and using the result as a liquid feed in your garden you resolve at least part of the weed problem.
But are there other ways in which you can perennial weeds and annual weeds into something useful? To which the answer is ‘yes’. But that’s another blog – a couple of which have links below for you…
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