Japanese knotweed ∗ How to get rid of the growing herb

Getting rid of Japanese knotweed forever

Which location is suitable?

In its homeland, Japanese knotweed often grows on volcanic ash fields. In Europe, the habitat extends over areas with moist soil, such as along bodies of water and wood-free riparian zones. But the plant also settles on ruderal areas, along the roadside, along embankments and forests. The Japanese knotweed is flexible in relation to the light conditions and grows excessively in both sunny and shady locations. The perennial is also stable, so that wind-exposed locations do not detract from its will to spread.

What soil does the plant need?

Japanese knotweed develops its resolute vigor in almost every type of soil. The perennial thrives mainly in nutrient-rich, moist soil; however, it has no inhibitions to settle in dry, sandy-loamy soil as well. Only in acidic bog soil and permanent waterlogging you will hardly find Japanese knotweed.

When is the flowering time?

One of the unmistakable characteristics of a Japanese knotweed is the pure white flower. In the period from August to October, the panicle-like inflorescences rise above the leathery, broad, egg-shaped leaves.

Japanese knoeterich in a pot

Cultivation in a pot still harbors the slightest danger of falling victim to the vehement urge to spread of a Kamchatka knotweed. If you want to dare to experiment, the bucket should have a volume of at least 30 liters. Any commercially available compost-based potting soil is suitable as a substrate. Before planting, spread a drainage made of gravel or potsherds over the water drain, because the plant cannot tolerate waterlogging in the long term. The maintenance program is limited to the following measures:

Water regularly when the substrate surface dries up
Fertilization is not necessary when repotting in fresh substrate every year
Radical pruning in autumn or late winter

Since Japanese knotweed sprouts even the smallest parts of plants, the clippings should not be disposed of on the compost. Immediately after pruning is the best time to repot the vigorous plant into a larger container.

Is Japanese Knoeterich Poisonous?

As an invasive neophyte, Japanese knotweed threatens ecosystems around the world. Regardless of this, the plant does not pose a toxic hazard to humans or animals. On the contrary, the young sprouts can be prepared like rhubarb or asparagus. In the Japanese art of healing, the root provides a tincture that has a beneficial effect on blood pressure and is said to lower high cholesterol levels.

What are the characteristics of Japanese knotweed?

During the flowering period from August to October, Japanese knotweed can be recognized by its white panicle flowers, which are quite pretty to look at. Outside of the flowering period, it is the leaves and shoots that serve as a distinguishing feature:

Leathery green leaves 12 to 18 cm long
Egg-shaped pointed and 8 to 13 cm wide
Arranged alternately on hollow shoots up to 300 cm long
Knotweed shoots often appear overgrown with red

There are tiny hairs on the leaf veins on the underside of the foliage that are barely visible to the naked eye. If you run your finger over it, you can at least feel the hair. After the first frosty night, the above-ground parts of the plant die off within a short time. The huge rhizomes in the soil, on the other hand, survive the winter undamaged and sprout again with vehemence at the beginning of the following vegetation period.

How does mechanical control work?

If you have discovered a Japanese knotweed in the garden, you need to act immediately. In the early stages, the following mechanical control methods give you a good chance of success in preventing an invasion:

Spreading area 1 to 4 square meters

Once the rhizomes of the Japanese knotweed have conquered a small area, you can fight the invaders with consistent digging and pulling out. Be careful not to leave any pieces of roots in the ground. Go to work with the spade or pickaxe as often as necessary until the buds are no longer visible.

Spreading area 4 to 20 square meters

If the knotweed already colonizes a larger area, you will not reach your goal with excavation. Now the plant should be mowed close to the ground every 2-3 weeks from April to October / November. Then clean the equipment thoroughly so that no parts of the plant are carried over to other regions of the garden. Experience has shown that this control method requires up to 5 years of patience.

In order to properly dispose of the excavated or mowed plant parts, smaller amounts end up in the household waste. A larger quantity of rhizomes, shoots and leaves is in good hands in the municipal composting facility or is transported to the bio-power plant for incineration. Kamchatka knotweed has no place on the domestic compost.

How does the fight with black foil work?

Cut Japanese knotweed from sunlight with the help of a sturdy, black film. Since photosynthesis comes to a standstill in the first place, the perennial dies over time. Of course, it takes a long line of patience of 1 to 2 years to triumph over the invaders. How to do it right:

Cover the entire infested area with thick, opaque film
Lay the edges at least 150 cm beyond the visible edge
Spread out pieces of foil overlapping by 10-20 cm and fix them in the ground

In this way you achieve at least a considerable weakening of the population, so that afterwards digging up all remaining rhizomes promises the best chances of success.

Are there any effective herbicides against Japanese knotweed?

The use of chemical herbicides in private ornamental and kitchen gardens is increasingly viewed critically. The negative consequences for the surrounding flora and fauna are too great. Hobby gardeners only resort to this remedy when all mechanical methods of combating the Japanese knotweed fail. Suitable preparations are broad spectrum herbicides, such as Roundup or glyphosate. Instead of a large-scale application, the partial administration of the agent has proven to be much more effective. How to do it:

Targeted injections directly into the stems every 4-6 weeks from June to September
Alternatively, brush the shoots and rhizomes with the herbicide
Do not spray near water

This control method is most effective immediately after mowing. An injection is very straightforward into the cut stalk, as this is hollow in Japanese knotweed. Experience has shown that up to 90 percent of the population is destroyed in the first year. However, further use in the following year is essential. Do not allow yourself to be led behind light by the apparent destruction of the knotweed, but stay on your guard in the following years.

How do I prevent invasive Japanese knotweed?

An effective prevention against Japanese knotweed is not to plant the perennial in the garden in the first place. The multi-faceted plant family of the knotweed plants offers a wide range of beautiful species and varieties that adorn the garden without completely subjugating it. The distinctive candle knotweed is one of them, as is the majestic bush knotweed.

Create your garden on a new plot of land, do not use excavated earth that could be contaminated with pieces of rhizome from a Japanese knotweed.

Is Japanese Knotweed Edible?

If you struggle with Japanese knotweed in the garden, you should still not turn a blind eye to its advantages. Knotweed leaves and roots are edible. The young shoots can be prepared for refreshing salads and make aromatic side dishes for meat or fish. When cooked, the leaves turn into a vegetable that is reminiscent of spinach.

Don't just dig up the roots to destroy Kamchatka knotweed. Peeled and boiled in salted water, they taste like asparagus. But be careful when disposing of uncooked plant residues, because they do not belong on the compost. The plant will sprout again from a 1 cm small piece of rhizome.