Japanese knotweed mercilessly overgrows any neighboring vegetation. The Federal Agency for Nature Conservation strongly advises against planting the immigrated neophyte. Read here how you can rid your garden of this all-consuming perennial in an emergency and prevent an invasion.
How can I control Japanese knotweed in the garden?
To combat Japanese knotweed in the garden, you can dig up and pull out roots, mow them regularly or cover the affected area with an opaque film. For large areas, several years of patience and careful disposal of plant parts are required.
Which location is suitable?
In its homeland, Japanese knotweed often grows in volcanic ash fields. In Europe, the habitat extends over areas with moist soil, such as along bodies of water and tree-free bank areas. But the plant also settles on ruderal areas, on the side of the road, along embankments and forests. Japanese knotweed is flexible when it comes to lighting conditions and grows equally excessively in sunny and shady locations. The perennial is also stable, so wind-exposed locations do not affect its ability to spread.
What soil does the plant need?
Japanese knotweed develops its resolute vigor in almost any soil condition. The perennial thrives primarily in nutrient-rich, moist soil; However, it has no inhibitions about settling in dry, sandy-loamy substrates. You will hardly ever find Japanese knotweed in acidic ericaceous soil and permanent waterlogging.
When is 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, broadly ovate leaves.
Japanese knotweed in pot
Cultivation in a pot carries the slightest risk of falling victim to the vehement urge to spread of a Kamchatka knotweed. If you want to try the 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 system made of gravel or clay shards over the water drain, as the plant cannot tolerate waterlogging in the long term. The care program is limited to the following measures:
- Water regularly when the substrate surface dries
- Fertilizing is not necessary when repotting into fresh substrate every year
- Radical pruning in autumn or late winter
Since Japanese knotweed sprouts from even the smallest plant parts, the clippings should not be disposed of in the compost. Immediately after pruning is the best time to repot the vigorous plant into a larger pot.
Is Japanese knotweed poisonous?
As an invasive neophyte, Japanese knotweed threatens ecosystems around the world. Regardless, the plant poses no toxic threat to humans or animals. On the contrary, the young sprouts can be prepared like rhubarb or asparagus. In Japanese medicine, the root provides a tincture that has a beneficial effect on blood pressure and is said to reduce high cholesterol levels.read more
How can Japanese knotweed be identified?
During the flowering period from August to October, Japanese knotweed is easy to recognize by its white panicle flowers, which are quite pretty to look at. Outside the flowering period, it is the leaves and shoots that serve as identifying features:
- Leathery-green, 12 to 18 cm long leaves
- Egg-shaped, pointed and 8 to 13 cm wide
- Arranged alternately on hollow, up to 300 cm long shoots
- Knotweed shoots often appear overflowing with red
There are tiny hairs on the leaf veins on the underside of the leaves 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 ground, however, survive the winter undamaged and sprout again with vehemence at the beginning of the following growing season.
How does mechanical combat work?
If you have discovered Japanese knotweed in your garden, immediate action is required. In the early stages, the following mechanical control methods give you a good chance of success in preventing an invasion:
Spread area 1 to 4 square metersOnce the rhizomes of the Japanese knotweed have conquered a small area, you can get rid of the invader by consistently digging and pulling them out. Make sure not to leave any root pieces in the ground if possible. Repeat the work with the spade or pickaxe until there are no more shoots to be seen.
Spread area 4 to 20 square metersIf the knotweed already colonizes a larger area, you won't achieve your goal by digging it out. Now the plant should be mown close to the ground every 2-3 weeks from April to October/November. Then clean the devices thoroughly so that no plant parts are carried away 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 mown plant parts, smaller quantities go into the household waste. A large quantity of rhizomes, shoots and leaves are stored in the municipal composting plant or are transported to the biopower plant for incineration. Kamchatka knotweed has no place in your home compost.
How does control with black foil work?
Use a sturdy, black film to cut Japanese knotweed away from sunlight. Since photosynthesis primarily comes to a standstill, the perennial will die over time. Of course, a long process of patience of 1 to 2 years is required to triumph over the invaders. How to do it right:
- Cover the entire infested area with thick, opaque foil
- Lay the edges at least 150 cm beyond the visible edge
- Spread the foil sections 10-20 cm overlapping and fix them in the ground
In this way you will at least significantly weaken the population, so that digging up all remaining rhizomes offers the best chance of success.
Are there effective herbicides against Japanese knotweed?
The use of chemical herbicides in private ornamental and kitchen gardens is increasingly being viewed critically. The negative consequences for the surrounding flora and fauna are too great. Only when all mechanical control methods against Japanese knotweed fail do hobby gardeners resort to this remedy. Broad-spectrum herbicides, such as Roundup or glyphosate, are not criticized without reason: they are suspected of contributing to insect deaths and various human diseases are attributed to the use of broad-spectrum herbicides. The herbicide affects our intestinal he alth and can lead to infertility. Skin diseases and cancer are also associated with it. Do yourself and the environment a favor and stop using such harmful substances.
How do I prevent invasive Japanese knotweed?
An effective prevention against Japanese knotweed is not to plant the perennial in the garden at all. The multifaceted plant family of the knotweed family offers a wide range of beautiful species and varieties that decorate the garden without completely subjugating it. The distinctive candlestick knotweed is one of them, as is the majestic bush knotweed.
If you plant your garden on a new building plot, do not use excavated soil that could be contaminated with pieces of Japanese knotweed rhizome.
Is Japanese knotweed edible?
If you have to deal with Japanese knotweed in your garden, you shouldn't close your eyes to its benefits. Leaves and roots of knotweed are edible. The young shoots can be prepared into refreshing salads and make aromatic accompaniments to meat or fish. When cooked, the leaves transform into a vegetable reminiscent of spinach.
Don't dig up the roots just to kill Kamchatka knotweed. Peeled and cooked in s alt water, they taste like asparagus. But be careful when disposing of uncooked plant residues, as they do not belong in the compost. The plant sprouts again from a 1 cm small piece of rhizome.
