Japanese knotweed (fallopia japonica) is a highly destructive and hardy plant. The Victorians introduced it to England around 1825 as an exotic perennial. Unfortunately its astonishing ability to cause major structural damage transformed it from an intriguing garden feature to a troublesome menace. Today it can be successfully eradicated but an understanding of its growth cycle is essential, as intervention at the wrong time of year will only make matters worse.
The early growth cycle: spring and summer
Knotweed first appears at ground level in April. The red and purple shoots are very similar to asparagus. They soon grow into dense clumps of thick, bamboo-like canes (or stems) and a crown of green leaves that can be easily identified by their distinctive heart shape.
The green stems are covered in characteristic purple speckles and they start to grow with great rapidity from June onwards. The stems can reach a height of approximately three metres in a couple of months. In fact growth spurts of up to 10cm a day throughout the summer are perfectly common.
In September and October, knotweed produces white flowers and the leafy foliage is at its most dense. However the onset of autumn is when the leaves start to turn yellow, which products a striking mixture of colours. They also begin to wilt at this point.
The winter cycle
From late autumn to early winter, the flowers fall and the stems start to die. They turn an orange-brown colour and look as though they’re decomposing, but they still remain upright throughout the winter. The fallen leaves form a dense layer at the base of the stems, which are thickly grouped and zigzag shaped.
There is no new growth during this period and its half dead appearance would suggest the plant has indeed expired. Regrettably this isn’t the case:
- Japanese knotweed remains dormant but very much alive below ground.
- The root system (rhizomes) is incredibly resilient, surviving freezing temperatures of minus 35°C.
- It also remains untroubled by lack of rainfall.
The rhizome network extends up to seven metres from the visible stems, so care must be taken not only in the immediate area but some considerable distance from it as well. If the roots are inadvertently disturbed and cut, the severed material will rapidly start to grow when the new season begins. Cut roots and stems produce long white shoots that quickly turn into new canes in the spring.
This is why winter is the most dangerous time in the knotweed growth cycle. It appears to be doing very little, but by spring the damage is done.
Still going strong
The continued survival of this invasive weed owes much to the fact that it’s a non-native species. It’s therefore impervious to natural diseases and predators in the British Isles. This allows it to dominate its surroundings and spread with impunity. Construction projects are the main cause of contamination, as soil is disturbed and tiny pieces of cut foliage are moved around by vehicles, equipment and feet. Extra care must be taken in the winter not to dig into the roots in the mistaken belief the plant is dormant.
Changes in the growing season
In recent years the traditional growing season has started to extend beyond April to October. Mild winters and warm damp summers have brought new patterns of growth. It’s not unusual to spot the early shoots in March and still see them emerging in November. If this were to continue unchecked, it would eventually increase the potential for the spread of knotweed all year round – a worrying prospect indeed.
This persistent weed is worthy of consideration because of the damage it will cause if left unchecked. It’s incredibly strong and has the ability to push through layers of tarmac and concrete. The damage to buildings can be so extensive that structural compromise is a real possibility. Consequently its presence can make mortgage providers reluctant to lend.
Fortunately it’s possible to deal with this damaging plant. Specialist help is on hand to solve even the most persistent knotweed infestations. For a free site inspection and guaranteed Japanese knotweed elimination, contact TP Knotweed today.