Plants are amazing things. They can fix most of the world’s problems if used correctly and are the source of a huge amount of what we need in our daily lives.
As permaculture folk we want to fix degraded land and create complex ecosystems and we do this with plants as they can do it quickly. Unfortunately their speed of growth can sometimes also be a negative thing. Thousands of dollars and volunteer hours go towards removing escaped vegetation; lots of poison, too.
Plant selection and use is a complex and controversial subject and is a reason why permaculture has sometimes been denigrated. Having studied and worked in both environmental restoration and permaculture I have some conflicted ideas about plants out of place aka exotics aka weeds. Some plants are brilliant, having multiple uses but some are just so good at propagating themselves they become rampant and have been banned from growing in certain areas, despite how useful they might be.
Personal responsibility is a strong ethos of permaculture, so I am going to outline my concerns with the trend of sharing seeds without clearly considering the consequences.
The term novel ecosystems (Hobbs, 2006) encompasses the many habitats on earth that have been altered in some way. Most habitats have been changed by the inclusion or removal of species, on purpose or accidentally; we can never go back to having pristine landscapes of purely indigenous species. Naturalised plants, that is introduced species which need no help to survive in a new place, have varying degrees of influence on bushland ecosystems, areas that are important repositories for endemic species including invertebrate populations. Earth care would have us protect remaining pre-settlement areas for health and wellbeing reasons.
Through clever design we can integrate a lot more food plants and other useful species into our environment but we need to be careful not to accidentally reduce biodiversity by letting many species be overgrown by one rampant one.
Using naturalised plants
There are many reasons to use existing ‘weedy’ or naturalised species in an area – biomass production, shelter and insect habitats, for instance. When trying to improve degraded sites the idea may be entertained that any plant that will grow in a place should be encouraged. If a site is degraded it needs any plant to grow there to protect and improve the soil. However some newly introduced plants can settle into an area too quickly, becoming costly to remove if they turn out to be a bit more voracious than one had hoped or expected.
Ideally, before planting, the permie designer would look around and see what is already nearby to fulfil their needs for vegetation before introducing new species to an area. If a plant is a declared or environmental weed in another place it is worth researching to make sure the same thing won’t happen on your site. There are always plenty of choices for all but the most marginal of conditions.
While I agree with Holmgren in his “Weeds or Wild Nature” essay that there has been demonisation of certain species, we should be careful not to dismiss the fact that some plants do escape into otherwise healthy bushland, changing the ecosystem structure. Many naturalised species are not encroaching any further than they have done since they settled in however I would suggest that there are some species recommended in permaculture readings that reproduce a bit too successfully where we are and as with all things, the better educated we are before we start, the less costly mistakes will be made.
Why are some plants more problematic than others
This depends on the plant’s life cycle, method of propagation and their self-defence mechanisms.
Self-seeding is good, sometimes.
Part of a good permaculture garden involves finding some edibles that will self-seed. For some plants this is fine, we water and look after the soil so it is good enough to support self sowing vegetables. Lettuces, rocket, parsley, and a range of other vegetables are a fantastic set of foodstuffs to happen on their own. Even parsley can take over a lot of ground space, which is okay if you love parsley and can share it around, but if you don’t like weeding, all you will end up with is parsley (make friends with a kebab shop and give it to them for their tabboleh).
Other plants self sowing isn’t so beneficial for suburban gardens, though. This is due to their size, rate of reproduction or some other reproductive behaviour. An example would be some extremely useful trees, Albizia lophantha and Acacia saligna. Both species kept coming up each year for a number of years in our garden and we would let them grow where they wanted. But only ever one at a time would come up and they are short lived and easy to prune. We knew we could manage them. Of course, in South Africa the Acacia saligna has become a big problem, changing ecosystem structure and fire regimes in the fynbos. It grows better there than it does here.
Some of the more common fodder trees will self-seed very easily, too, such as Leucaena leucocephala and Tagasaste. In some areas the seeds will not be viable but where they can take hold and aren’t being pruned regularly for fodder or mulching, especially while in flower, there could soon be thousands of shrubby trees popping up. Management of this biomass is vitally important, making a huge difference to the amount of shade or sun you have and how much mulch and sticks for firewood you can end up with.
Weed potential depends how the plant produces seeds and how many seeds it produces.
Plants will grow and reproduce within their natural range and be controlled by climate, soil type and natural seed or leaf eaters; however outside of that, where conditions are more favourable, and no biological controls exist, there is the chance of over population through success in competition. In some cases the intruder may overtake all other plants in an area, creating a monoculture in a previously diverse place.
There are a variety of ways that a plant can produce seeds or other propagules that can escape in large enough numbers to potentially become problematic.
Windblown seeds – plants in the daisy family (Asteraceae) make thousands and thousands of seeds, which can then blow away on the lightest breeze. This includes dandelions, wormwood, sunflowers, tansy, lettuces and globe artichoke, the latter closely related to prickly thistles which are probably not much fun to remove by hand; removing them by pig might work though and be more fun.
Pods – some seed pods can throw seeds many metres away from the parent plant when they dry and pop open, or they make hundreds of seeds per tree. It’s tempting as a new permie to grab anything that looks like a nitrogen fixer and stick it in your garden. It’s how I got the plant that has caused me the concern to write this article. I picked a few seeds from a leguminous tree in the garden of my old permaculture teacher, without asking what it was. Leucaena, I’m looking at you! While this plant is highly recommended for chop and drop mulch it needs a decent amount of upkeep to prevent it spreading itself throughout the neighbourhood.
Suckers – these upright eruptions from the roots may be prickly and hard to remove depending on the species. Robinia pseudoacacia, a nitrogen-fixing deciduous shade tree is renowned for this and may produce many upright suckers with spines if the parent tree is removed or even trimmed. We have a large honey locust (Gleditsia tricanthos cv Sunburst) tree that has only suckered since we decided to chop a few branches off.
Berries and fruit – Blackberries, olives and cactus are renowned for this method of dispersal. Birds or animals eat the fruit and then “drop” the seeds elsewhere with a bit of bonus fertiliser. Blackberries are difficult to control due to their vicious prickles, which provide protection for the birds that then spread the seeds. They also sucker, rooting into the ground where the stems touch soil. It’s a triple threat.
Bulbs – some bulbous plants can reproduce two ways, for instance, gladiolus makes bulbs and seeds. This makes them twice as annoying to remove and gives good reason to pick all the flowers before they form seed heads. Bulbs can also be difficult to control as many make tiny side bulbs that break off when the plant is pulled out, allowing more plants to come back in following years.
Special consideration needs to be given for destroying some kinds of weeds.
Creepers and climbers – Creepers and climbers are in a special class of their own, as they can often make seeds and also sucker, poking roots into the ground along their stems where they touch the ground.
Kudzu (Pueraria lobata) can be a really useful plant for grazing animals and erosion control. However when grown in an area that has warmer winters than its natural habitat, it has no overwintering period to kill off excess plants. This plant can move a long way while being fed from many root zones and in parts of the USA has smothered large areas, burying buildings and killing trees.
Management is the key issue here. Removing flowers of a lot of these plants will save a lot of effort later on by preventing seeds forming. Height management is vital for keeping fruits to a reachable height so the plant can be netted if that is an option for controlling fruit or seed spread. Some perennial plants or large annuals can be fairly easily controlled by cutting just below the plant into the root zone, slicing the main plant part from its water and food supply. This also disturbs the soil much less so more weed seeds don’t get exposed.
Be aware of what seeds you are sharing.
I am not saying no weedy plants should be used in permaculture systems because any plant can be a weed if it is in the wrong place and we love weeds; they are pretty vital to permaculture and land restoration in some cases. What I am stating here is that there are a FEW really bad plants in terms of how readily they spread. I think we need to consider these plants and be aware of what we are sharing. If you are handing over seeds be honest about how hard that plant might be to keep under control; if they are in a different part of Australia definitely check that the plant isn’t a weed.
It is too easy for people to swap plant propagules and there isn’t always a description or warning of any sort whether the plant has potential issues. Indeed, the plant may behave totally differently in the two places, especially if the rainfall or soil is better in the new place. Just be aware that some plants can out-compete all others, reducing your carefully designed food forest.
WHAT can we do as responsible gardeners?
Be aware of who you are sharing seeds with. Do they live near bushland? Is there a less invasive plant they could be using instead? I am very unlikely to pass on seeds of a plant I know can make hundreds of seeds unless I have quizzed them a little regarding their ongoing maintenance of a garden site.
Also, be careful at swap meets, as sometimes people can be selling plants that are potential weeds and they may not even know.
There are still thousands of species and plenty of responsible food growers out there. Just have a little think before you give seeds away to that thing you’ve been battling to control in your own garden, eh.
Holmgren, D. 2013. http://permaculturenews.org/2013/11/12/weeds-wild-nature-permaculture-perspective/
UCDavis IPM: http://ucipm.ucdavis.edu/PMG/PESTNOTES/pn74139.html