Weeds have long been maligned for their invasion in our gardens, lawns, and pastures. Some would say they have earned their reputation due to their competition with agricultural crops. Gardeners and Farmers the world over seek to destroy or remove them in a variety of ways. But if we look a little deeper we will see that nature is attempting to repair the soil and weeds are the tools with which it begins the process.
What is a Weed Anyhow?
Each jurisdiction has its own definition and policies around weeds and their control. Here are just a couple to give you an idea of the varied ways that weeds may be considered.
A weed may be defined as any plant or vegetation that interferes with the objectives of farming or forestry, such as growing crops, grazing animals or cultivating forest plantations.
https://teara.govt.nz/en/weeds-of-agriculture/page-1
This definition assumes that we are in dominion over the plants, and indeed the planet. Personally, I find this definition to be egocentric and not very helpful but the fact remains this is how most people see weeds. They are simply a problem.
Some cultures, in fact, do not have a word for weeds, as all plants are considered useful. If we take this a little further then the following definition is a little better.
A weed is a plant considered undesirable in a particular situation, “a plant in the wrong place”…..the term “weed” has no botanical significance because a plant that is a weed in one context is not a weed when growing in a situation where it is in fact wanted, …..
Wikipedia
Within Permaculture circles two things are commonly said and to whom I cannot attribute an original source.
- Nature abhores a vaccum – meaning that were there is open space nature will seek to fill it.
- A weed is merely an out of place plant. This statement makes us think about the possible uses for this plant or weed if you like. Nothing in nature is wasted and therefore everything has a purpose. We simply need to find it.
So what are the weeds telling us?
Before we race out to attempt to control weeds we should seek to evaluate what is going on in the ecosystem. What conditions are present that nature is trying to correct? What has happened or been done to create the condition? How can we assist nature to rectify the problem? Only then will we have the information that will allow us to determine if the plant we are eyeing as a weed is truly out of place or is it providing a service we are unaware of? In the foreword, to Impact of Environmental Weeds on Biodiversity, Gerard Early wrote, “Key questions that need to be asked before control programs are undertaken for environmental weeds include determining the impact of weeds on native species and ecosystem functions, the threshold densities at which there is little or no impact of the weed on conservation values, and what factors can be manipulated to reduce that impact.
Nature wastes nothing, everything in nature has a purpose and a role to play. Many weeds not only can tell us about the soil condition but also about our management practices. For example, over stocking of grazing animals will have the ground bare and compacted, erosion from wind and water but nature will do everything in her power to heal the land. This may be with the use of vegetation to reduce erosion and hold the soil together or it maybe in the use of vegetation that covers the soil and begins the decompaction process.
Weeds and Nature have a language and it is useful for us as gardeners and farmers to understand these patterns and learn to read their language. Reading our landscapes is half of the battle but this is not taught in schools or garden books. We know that Dandelions have long taproots and are often very difficult to pull out but did you stop to consider that the taproot has another function. It is opening the hardpan of the soil and allowing water and air to penetrate. This is just one example of the pattern language we must learn to read.
So we now understand that weeds can tell us a lot about what is going on below the ground and above it. This handy table shows some common weeds and what we can learn about the soil condition. While it is not exhaustive – there are quite literally thousands of plants that have been listed on the worlds’ weed databases, it does show some common weeds that we battle with. Where the weeds are dominant or large in number they are potentially giving us clues to the needs for repair.
| Common Name | Botanical Name | What is it telling us? |
|---|---|---|
| Dandelion | Taraxacum Officinale | Low Humus, Compacted Soil, V-Low Ca & P, V-High K & Mg |
| Fireweed | Senecio Madagascariensis | Low Humus, compacted, Anaerobic Bacteria, Low fertility, V-Low Ca & P, High K |
| Nutgrass | Cyperus Rotundus | Low Humus, compacted, little biology, can host nematodes, V-Low Ca & P, High K & Mg |
| Sow Thistle | Sonchus oleraceus | Good Drainage, Low Humus, Compacted, High N+, K, Mg, V-Low Ca & P |
| Kikuyu | Pennistem Clandestinum | Compacted, low humus, little bacteria, V-Low Ca & P, High K, -High Mg |
| Wild/Green Amaranth (Pigweed) | Amaranthus Viridis | Little organic matter, low soil bacteria, V-Low Ca & P, V-High K & Mg |
| Cobblers Pegs | Bidens Pilosa | germinates in disturbed ground, Low Humus, Compacted Soils, V-Low Ca & P, High K & Mg |
| Scotch Thistle | Onopordum Acanthium | Compacted, poor drainage, limited bacteria, low humus, Low Ca, High K & Mg |
| Blackberry Nightshade | Solanum Nigrum | low soil humus, anaerobic bacteria, compacted soils, V-Low Ca & P, High K & Mg |
| Broadleaf Dock | Rumex Obtusifolius | poor drainage, little bacteria, high salt, V-Low Ca & P, High K & Mg |
| Bracken Fern | Pteridium Esculentum | very little organic matter, sandy well drained soil, very invasive, often appears after fire, V-Low Ca, High K & Zn |
| Marshmallow | Malva Parviflora | low humus, compacted soil, poor drainage, anaerobic bacteria dominate, V-Low N+, Ca, High K & Mg |
| Lantana | Lantana Camara | Low humus, well drained, invasive thickets, V-Low Ca & P, High K & Mg |
| Purslane | Portulaca Oleracea | very low humus, compacted soil,low moisture, high salt, V-Low Ca & K, High P & Mg |
| Plantain | Plantago lanceolata | Low Humus, Compacted Soil, V-Low Ca & P, V-High K & Mg, Often found in poor pastures and a sign that pasture needs renewing. Palatable fodder for stock |
| Khaki Burr | Achyranthes Repens | compacted, poor drainage,anaerobic soil, little humus, Low Ca, High Mg |
| Burr Medic | Medicago Polymorpha | high bacterial, alkaline soil, nitrogen fixer used in pasture and orchards, Low Ca & P |
| Ragweed | Ambrosia Artemisifolia | compacted soils, low humus, V-Low Ca & P, V-High K & Mg |
| Chickweed | Stellaria Media | compacted soils, low humus, indicative of wet soil, V-Low Ca & K, V-High P & Mg |
| Spiny Burrgrass | Tribulus terrestris | anaerobic, sandy, well drained, V-Low Ca, V-High Mg, High P & K |
| Caltrop | Tribulus terrestris | abundant on sandy soils, anaerobic bacteria, low humus, Low Ca & K, High P & Mg |
| Hemlock | Conium maculatum | anaerobic, prefers damp soil, Low humus, compacted, Low Ca, High K, Mg, & Zn |
| Mother of Millions | Bryophyllum Species | rocky, poor soil, dryland, neutral-acid soil, in leaf litter, Low Ca & P, High K & Mg |
| Flat Weed | Hypochoeris radicata | often misidentified as dandelion, poor soil, low humus, compact, V-Low Ca & P |
| Pattersons Curse | Echium plantagineum | sandy acidic soils, low pressured pastures, low humus, compacted, V-Low Ca & P, High K & Mg |
| Shepherds Purse | Capsella bursa-pastoris | wide range of soil types but more common on heavy greyclay & red soil, anaerobic, poor humus, Low Ca & P, High K & Mg |
| Blue Heliotrope | Heliotropium amplexicaule | Low Humus, Compacted well drained soil, Low fertility, acid loving, Low Ca & P, High K & Mg |
Acknowledgment of sources – Michael Wardel of Savour Soils; JayMcCaman “When Weeds Talk”; Brown Book by Corangamite Catchment Management Authority; Weeds.org.au;
Beneficial Weeds
Many of the so-called weeds are in fact beneficial in a number of ways. The List below shows just some of these. Imagine looking out at your vegetable garden to find that instead of weeds calling to be pulled you now find that some are now part of your regular diet and are actively cultivated.
| Common Name | Botanical Name | Comment |
|---|---|---|
| Bashful mimosa | Mimosa pudica | Nitrogen Fixer, Ground cover for tomatoes, peppers, attracts predatory beetles, used as a natural ground cover in agriculture. |
| Caper spurge | Euphorbia lathyris | Repels Moles, Fodder for some domesticated animals. French folklore as a purgitive/emetic |
| Nettles | Urtica dioica | Companion Plant for Broccoli, tomato, valerian, mint, fennel, young plant parts are edible, as is much of the plant when blanched, herbal tea, as a fiber crop. Its juice was once used in the place of rennet in cheese-making. It was also a source of “green” for dye. It can still be used as a high-protein additive in animal feed, once dried. |
| Wild Garlic | Allium vineale | Companion for fruit trees, nightshades (tomatoes, peppers, potatoes, etc.), brassicas (cabbage, broccoli, kohlrabi, etc.) carrots, can be eaten as chives or green garlic |
| Wild Mustard | Brassicaceae | Companion for Grape vine, radish, non-mustard brassica, including cabbage, cauliflower, broccoli, traps brassica pests including aphids, attracts ladybettles |
| Wild Rose | Rosa | Repels Rodents and Deer, companion for Strawberries, grapes, roses, traps japanese beetles, Rose Hips used in herbal teas and jams. |
| Borage | borago officinalis | Companion for legumes, brassicas, tomatoes, some fruit trees, attracts predatory wasps, widely used medicinally, Flowers and Leaves edible in salads. |
| Dandelion | Taraxacum Officinale | Long taproot aerates soil, attracts beneficial insects and pollinators, widely used to make coffee substitute, all parts edible in season |
| Clover | trifolium | Companion for brocolli and cabbage, attracts beneficial insects, nitrogen fixer, cover crop, living mulch, do not plant near tomatoes. |
| Chickweed | Stellaria Media | Often grown for poultry feed, can also be used in salads |
| Blackberry | Rubus fruticosis | Berries eaten, stands can be used as fences, fodder for goats. |
| Burdock | Articum | edible particularly young leaves and also roots |
| Flatweed | Hypochoeris radicata | edible leaves, roots after roasting |
| Purslane | Portulaca Oleracea | leaves edible in salads or stirfry |
| Shepherds Purse | Capsella bursa-pastoris | leaves and seedpods edible in stirfrys |
| Cowpea | Vigna unguiculata | Nitrogen fixer, attracts ladybeetles – can be used as a trap crop around other crops – edible. |
While many more benefits and relationships exist between our plants and weeds it wise to note that all flora has an advantage and a disadvantage. It is important to understand the relationships and functions of each element within the ecosystem. That is to say if you wish to introduce a new element or species to an ecosystem, have you checked the balance of the system first? Is it in balance or out of balance? If you introduce a new element what will it bring to the ecosystem and the relationships within it and what will it take? Is there benefit to the overall system with the introduction of the new element?
We cannot continue to simply add or subtract from our gardens with out understanding the relationships and functions of each element. While all weeds have a purpose we should not be rushing out to plant them in an area they have not previously inhabited. Plants like all other life on this planet has evolved and continues to do so. Bringing something into a fragile environment whether good intentioned or not encourages breakdown of systems and evolution of lifeforms that may not benefit the system in the long term.
How do we use weeds to our advantage?
Notwithstanding the caveat above, there are ways in which we can use weeds and other plants to our advantage. We know that cowpea is a nitrogen fixer and that it attracts beneficial insects such as ladybeetles. So if we were to plant cowpea around a crop of cotton or mustard greens then we know that the ladybeetles will have plenty of aphids to chomp on in the crop and the soil is being fertilised at the same time by the cowpea.
In addition to this we can use weeds and other plants to mine minerals for us and then use the entire plant prior to seed set to provide those minerals to other plants in the form of mulch, compost or fertilising liquids. A good example of this is comfrey – known as a dynamic accumulator. This means it is mining minerals deep from within the soil and storing them within. Comfrey mines nitrogen and magnesium. When we utilise the leaves of the plant to make fertiliser we are effectively putting back into the topsoil what was absorbed from deep down.
So when you look at the list of weeds above you can see that each plant indicates a deficit of minerals and an overabundance of others. Each plant in the garden is taking the excess or bringing the deficit back into harmony. Can you really look at weeds the same way again?
For a free resource to download and print go here.
