Gardeners - Tackling Invasive Weeds & Plants

What to do if you come across invasive plants or weeds

Armed with the knowledge that you or your client have an invasive weed or plant species to ‘manage’ within their garden - what do you do next?  

The 1st thing to do

The first job is to establish the extent of the invasive weed infestation and what needs to be done immediately to prevent further spread on or off site.  This is called a biosecurity plan. (note: more information about biosecurity plans via the 'Code of Practice') 

This is more challenging for some invasive weed/plant species than others. For example, Japanese knotweed may be one of the most difficult invasive weeds to control, but only spreads by vegetative means.  For Japanese Knotweed, biosecurity measures could be as simple as creating a cordon to prevent soil disturbance and some warning signage with a brief explanation.  

The above may sound relatively easy, but you also must consider that wildlife such as badgers, rabbits and foxes don’t read, so a bit of mesh fencing is normally recommended too!  A biosecurity plan should also include considerations about infestation risks from the surrounding area e.g. if there is more knotweed nearby but not on your client’s land.

The 2nd thing to do

Perhaps your most significant ‘duty’ is to recognise invasive weeds which may be harmful to health e.g. Giant Hogweed.  This a few other umbellifers (e.g. Poison hemlock, Wild carrot; albeit these latter species are not ‘listed’) are potentially harmful to humans (and some other animals like dogs) by skin contact.

Clearly, if Giant Hogweed is present, the biosecurity advice above applies (albeit the risk of spread is more generally due to seed dispersal) but you should make it clear to the client that due to the additional risks to human health, if public access is possible or likely, treatment or removal ought to be considered urgently. 

Controlling/Managing the invasive issue in the garden

Managing invasive weeds is a job that requires careful planning and will normally involve interventions lasting several years followed by an even longer monitoring period (checking for signs of re-growth or new infestations).  

The practical aspects, getting ‘on-top of’ the invasive weeds found, usually involves two approaches (separately or together) that professional gardeners will be familiar with: 

1. herbicide treatment* or
2. digging/excavation.  

However, selecting the best approach requires a degree of familiarity with the characteristics of each species.  Fortunately, the PCA has published a book (Practical Management Guide) based on our members’ experience and this may enable small jobs to be tackled confidently.  

There may however, be many situations in which the best advice for your client is to engage with a local PCA member who can provide an Invasive Weed Management plan fully compliant with the principles of Integrated weed control.  All our members work to The Amenity Standard and can offer long-term guarantees backed-up by appropriate insurance if required for e.g. mortgage purposes. 

PCA members can guide you through the options available, the consequences for land use in each case and the likely costs. Key considerations will be things like whether the area is likely to be disturbed (for future landscaping or routine maintenance e.g. hoeing, adding/removing bedding plants etc.).

*Alternatives to herbicide treatment for managing plants in situ are available; these include, for example; heat treatments, bio-control and cultural techniques but using these methods is still somewhat experimental as far as most invasive weed species are concerned. A recent blog on Integrated Weed Management Plans and invasive weed management is - here (link).