Churchyard Nature Note with Andrew Tompsett

August 2017

Alien plant watch

Much has been written about how certain alien, non-native plants or neophytes have become established in our gardens and countryside. One of the most pernicious is the so-called Japanese knotweed (Fallopia japonica) and much has been said about its vigorous growth, persistence of the rhizomes (underground stems) and capacity for spreading, overwhelming native plants and blocking waterways. Government laws are in place expecting landowners to control and eliminate this invasive species, in particular avoid its spread on site or by removing contaminated soil and vegetation. This is worth remembering when selling a property.

Twenty years ago our living churchyard policy was launched and I remember there being two patches of Japanese knotweed. The advice of Cornwall Council was to eradicate it before it became a greater problem. At that time control measures consisted of treating the plants with the well known herbicide ‘Glyphosate’ and I recall it required follow-up measures in the next two years after which it was very much reduced for several years.

So imagine the surprise and disappointment when we saw some significant re-growth of this unwelcome weed this year and growing in exactly the same places as it was some 20 years before. Prompt control action has been taken.

All we can do now is closely observe the area next year and subsequent years to see whether it reappears. Our past experience suggests it probably will shoot again despite the control treatment.

It is worth mentioning how we dealt with the large shoots we cut off. It is well known that if left on the ground or composted, new plants will grow from them. The best treatment for severed shoots is to kill them by drying them completely. This we have done by tying them in a large bunch and hanging them from a tree so that they cannot touch the ground. Later they can be burned. It is actually against the law to move them to another site, even after burning, since they may still be viable.

Studies of Japanese knotweed show that underground roots can reach deep (2 metres) into the ground and also spread laterally for up to 7 metres. The roots are thick and clearly very ready to sprout elsewhere, even if cut into small pieces. Hence the danger of any soil or plant material being moved to a new site. The plant’s ability to shoot up through tarmac and concrete is quite terrifying.

The means by which Japanese knotweed has spread around the world is very much a matter of not appreciating the amazing regenerative power of the plant. It was initially introduced as an ornamental plant for large Victorian gardens about 1825 and it is also suggested as fodder plant. It was probably not long before those early gardeners found it too large a plant and probably threw it out without a further thought since when it has become established in the wild between 1920 and 1940. Now we are faced with an expensive and potentially insoluble problem and Cornwall is among some of the worst afflicted counties.

This year I have experienced another case of plant persistence. Bracken shoots have appeared in my garden lawn which has been closely mowed for some 40 years. This looks like another case of long term survival! Bracken is a huge national problem as it smothers vast areas of potential grassland. It is present in the churchyard but is a lesser problem than Japanese Knotweed but one with which the next generation of churchyard managers will have to combat.

Andrew Tompsett