Wiki says "The young stems are edible as a spring vegetable, with a flavor similar to mild rhubarb. In some locations, semi-cultivating Japanese knotweed for food has been used as a means of controlling knotweed populations that invade sensitive wetland areas and drive out the native vegetation.[9] Some caution should be exercised when consuming this plant because it contains oxalic acid, which may aggravate conditions such as rheumatism, arthritis, gout, kidney stones or hyperacidity.[10]
Both Japanese knotweed and giant knotweed are important concentrated sources of resveratrol, replacing grape byproducts. Many large supplement sources of resveratrol now use Japanese knotweed and use its scientific name in the supplement labels. The plant is useful because of its year-round growth and robustness in different climates.
Japanese knotweed is a concentrated source of emodin, used as a nutritional supplement to regulate bowel motility. The roots of Japanese knotweed are used in traditional Chinese and Japanese herbal medicines as a natural laxative. The active principle responsible for the laxative effect is emodin, present in its natural form as a complex of its analogs. Emodin has a mild laxative effect in doses of 20 to 50 mg per day."
I thought it was carcenogenic, think I'm getting mixed up with Ragwort..
Personally, I think it ought to be eradicated, having seen its effects on my brothers garden, and the pavement outside. 3 or 4 inches of tarcam is no problem.. Just not too happy about the method.
The best "free" food has to be nettles, great spinach substitue, and makes fantastic wine (liquid, not sound!). This could start a whole new topic of what we eat..