Thursday, June 19, 2014
It’s good to share, but beware. Plants and personal responsibility.
This article will also appear in the PermacultureWest enews.
It’s good to share, but beware. Plants and personal responsibility.
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. Other plants self sowing isn’t so beneficial for suburban gardens, though. This is due to their size, rate of reproduction or some other 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.
Weediness potential depends how the plant produces seeds.
Some plants will behave within their natural range and be controlled by natural seed or leaf eaters however outside of that, where soil or rainfall are more favourable, and no biological controls exist, there is the chance of over population.
There are a variety of ways that a plant can produce seeds that can escape.
Windblown- plants in the daisy family make thousands and thousands of seeds, which then blow away on the lightest breeze. This includes lettuces and globe artichoke, closely related to prickly thistles.
Pods - some seed pods can throw seeds many metres away from the parent plant, or make hundreds of seed per tree. Leucaena, I’m looking at you.
Suckers - may be prickly and hard to remove, Robinia, a nitrogen-fixing deciduous shade tree is renowned for this.
Prickly and spines: Blackberries, cactus. Ouch. They can be spread by animals eating them and dropping the seeds or they may have seeds that attach to an animals fur, and spread that way.
Berries and fruit - birds carry seeds away and drop them off with a little free fertiliser. Olives easily spread into bushland this way. Blackberries - spread by seed and by sucker and are really prickly as well. Triple threat.
Bulbs: some can reproduce two ways, ie gladiolus makes bulbs and seeds.
Plants that creep and climb: kudzu, really useful, really buries houses.
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. 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. Some plants can outcompete 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.
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