Following the revelation that our village is under threat from invasive species, Amanda Borrill hears from resident and expert botanist David Dives who offers his guidance on how to weed out aliens and explains what we can do to get this growing problem under control.
A recent presentation by local resident David Dives to Histon & Impington Parish Council has revealed an increasing threat across our village gardens and woodland from invasive plant species.
Retirement in 2014 offered David the opportunity to focus on his lifelong interest in botany; linking up with the County Recorder of Botany Essex to work on a county-wide botanical survey – an opportunity which would lift his botanical skills to an expert level. David arrived here in Histon in 2020 and has since become a valuable contributor to the community; becoming involved with Histon and Impington Green Spaces, eventually as a Trustee, advising on the maintenance and development of Long Meadow and Croft Close Nature Reserve. He is, however, keen to point out that this survey of the area is in no way connected with HIGS and his approach to the PC is as a resident and not as a representative of HIGS.
A full botanical survey of our surrounding area (12 sq Km) was conducted by botanist David, covering all public, and some private, areas in Histon and Impington. Speaking at full Council on 16 February, David presented the results of his survey which identified all plants growing in the survey area – including invasives.
Know the culprits
“The Wildlife and Countryside Act 1981, includes two schedules that pertain to our flora”, explains David. “Schedule 8 lists special and rare plants that are fully protected from being collected or destroyed, but Schedule 9 lists some alien invasive plants which ‘It is an offence to plant or otherwise cause to grow in the wild, even though it is legal to keep the plant in your garden or for research. We have three Schedule 9 plants in H&I that are increasing rapidly and should be controlled”.
The three Schedule 9 plants of immediate concern are:
Allium triquetrum Three-cornered Garlic
Monads before 2004 – 2. Monads now – 28.
Allium paradoxum Few-flowered garlic
Monads before 2004 – 18. Monads now – 78.
Lamiastrum galeobdolon subsp. argentatum Garden Yellow Archangel
Monads before 2004 -10. Monads now – 163.
The Monad counts indicate a plant’s spread over the past 20 years in Cambridgeshire. The counts show how many monads have a record of the plant being present. “For a monad to count it must have at least ONE of the plants, but might have thousands, or even millions”, David explains. “These numbers give an idea of spatial spread across the county but do not measure the quantity, although it would be surprising if the quantity present didn’t correlate with the monad count”, he says.
The art of detection
So, how easy is it for our village gardeners to identify an invasive alien lurking in their flower bed?
“Both Garlics have stems triangular in section, with three very acute corners. Crushed leaves smell strongly of onion. Flowers are white, from April to May. Leaves die back in June and flop over to lie on the ground suppressing nearby native vegetation emerging in early summer. They can quickly colonise a garden, becoming the dominant plant”, reveals David.
“The Garden Yellow Archangel is easily separated from the native Yellow Archangel by the silver markings on the leaves – sometimes with a purplish centre. A plant of shady places, spreads rapidly via horizontal creeping shoots rooting as they grow (stolons). A small fragment of this plant will take root rapidly.
“It is highly invasive”, he warns, “rapidly spreading across a woodland, along a hedge, or a roadside verge. It shades out native vegetation, but the big fear is that, given the chance, it will hybridise with the native Yellow Archangel, and thus destroy a valued native population”.
Eradication
There are a number of populations of these three invasive plants across Histon and Impington. David’s talk to the Parish Council highlighted some public sites where these plants are spreading, as well as some private sites where, for various reasons, eradication may be more challenging.
David tells more. “Where the occurrence involves just one property I usually try first to talk to the landowner offering ‘a word to the wise’ and the issue can be dealt with.
“My talk to the Parish Council was to mention cases where the infestation needs a different approach: landowner not resident in the village; also in the public space; or several properties involved where eradication will require a coordinated plan. I hope, following my talk, the PC (perhaps via its Environment committee) will pick up the baton.
“Infestations in the village have been caused by garden waste being dumped over the back fence of a garden, or by a wheelbarrow into the local woodland patch. In the case of the Alliums, plants spilling out of a garden, under the fence or through the hedge, with flowers lying on the pavement or footpath – will inevitably spread their seed or bulbils to neighbouring properties. Residents and gardeners need to be mindful to dispose of garden waste responsibly, and keep their boundaries clear”.
Under the The Wildlife and Countryside Act 1981, a gardener ‘must take reasonable measures to ensure they do not spread beyond your boundary into the wild or onto neighbouring property‘.
Ensuring safe removal
Removal of these invasive plants once they become established is difficult. Fundamentally there are just three ways, says David:
- Dig them out. Difficult in a woodland setting as tree roots make it impossible to find all the roots or bulblets. Impossible to get all the roots/bulbs in one go.
- Use a systemic weed killer in the growing season. A patient gardener with a small infestation can use one that is painted on the leaves. A general spray of course will kill other flora, and be detrimental to insect life.
- Apply an impervious mulch – plastic sheeting, thick cardboard, or an old carpet. Leave in place for the whole growing season, and be prepared to repeat.
Whichever method (or combination of methods) eradication is likely to require two or three applications in successive years.
Contaminated waste
If the plants are uprooted or dug out, the big question that follows is – ‘what to do with the waste’?
“Clearly, throwing over the back fence is NOT an option, easy as it might be”, says David. “Gardeners should be aware that having removed a Schedule 9 plant they have Contaminated Waste on their hands, and it must be disposed in a manner that is unlikely to give the plant an opportunity to colonise a new site”.
Safe suggested methods are:
- Burning (if your situation permits)
- Seal up in a plastic sack and put into your BLACK bin
- Seal up in a black sack and leave outside in full sun for a couple of months – the plants/berries etc will cook
“Definitely do not put into the green bin!”, stresses David. “These plants are tough cookies! They may well survive the composting process, and go on to found a new colony where the compost is used to feed the soil”.
Next steps
If a resident is concerned that they may have a Schedule 9 plant present, they can email the Parish Council on helpdesk@hisimp-pc.gov.uk. They will be able to offer advice or connect residents with David for further guidance.
Where the Parish Council has contact details for a known address, a letter can be sent advising if a known invasive plant has been identified on their property. They will then offer further advice on what steps the householder can take to remove it.
The Parish Council Environment Committee will continue to work alongside David to identify and eradicate known problem areas.
More details on the rules surrounding invasive non-native plant species in England and Wales can be found here. For information on Cambridgeshire invasives, see the website for the County Recorder of Botany for Cambs here.
