Japanese knotweed to 'dominate' gardens this summer after April frosts

Helena Horton
·3-min read
Japanese knotweed can grow to be huge if not tackled
Japanese knotweed can grow to be huge if not tackled

Japanese Knotweed is to "dominate" gardens after April frosts delayed or killed other plants, experts have warned, in what could be a bumper year for the invasive pest.

While in the winter, the plant lies invisible, deep in the ground, it springs up as the weather warms and the frosts stop. It is extremely hardy, and the cold spring will not have dampened it - but it will have weakened killed off the plant's competitors.

The plant forms dense stands of tall bamboo-like canes which grow to 2.1m (7ft) tall, and can destroy houses and gardens. It can even devalue land and property and lead to the refusal of mortgages on properties affected by it.

Experts at trade body the Property Care Association (PCA) have warned that late season frosts and dry weather may cause Japanese knotweed to “come back even stronger” this season.

The PCA’s Invasive Weed Control Group technical manager Dr Peter Fitzsimons said that as other plants have been knocked back by the recent frosts, the weed could "dominate".

He told Horticulture Week: “Many plants in the UK have been knocked-back by late season frosts and dry weather in April, but the sheer resilience of Japanese knotweed means it will be in a position to come back even stronger. While almost every plant has struggled with the weather conditions, it’s likely that this will help Japanese knotweed to dominate even more that it normally does because it is such a resilient plant.

“When some warmer weather and spring rains come along, we are set to see it take off, using its food reserves stored below ground over winter. If it does dominate, simply put, that means more damage potential and capacity for the plant to spread.”

Guy Barter, the Chief Horticulturalist for the Royal Horticultural Society told The Telegraph that the weather conditions recently mean that weeds, including knotweed, will spring up as if out of nowhere.

He explained: "This is the coldest spring for eight years, I understand, and all plants are delayed by the cooler air and soil compared to recent years. When the weather finally turns warmer the sun will be high in the sky and the nights even shorter so the heat will be strong and with much moisture still in the soil from the winter rains plants will grow very rapidly. We expect a flush of weeds every early June and this year it may well be more sudden and concentrated than usual. This includes Japanese knotweed and other invasive weeds. Gardeners would be wise to be ready to manage weeds as they appear before they get a hold."

Removing knotweed can be very difficult, and often requires homeowners to hire professionals to excavate it, as cutting it back just causes it to spring up again, due to its rhizomes in the ground.

Mr Fitzsimons added: “Currently, the law focuses on landowners to control and remediate Japanese knotweed infestations, particularly near houses, as soon as they come to light. In the case of property development, removal by excavation is often the only viable solution and this needs to be handled by qualified knotweed surveyors.”