Himalayan balsam is a valuable late nectar source and a seriously damaging invasive plant, and both are true at once.
The plant's nectar productivity and its ecological damage are both well documented. It shades out native riverbank vegetation, dies back completely in autumn leaving bare eroding soil, and spreads by explosive seed dispersal and water. In Britain it is an offence to plant it or cause it to grow in the wild. Its honey value is a genuine fact and not a mitigation.
What this does not claim: This does not claim the honey itself is harmful, nor that beekeeping spreads the plant. It also does not claim the nectar benefit offsets the ecological damage — the balance of evidence runs the other way.
- Assessment Report on Pollinators, Pollination and Food Production — Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) (2016) · Systematic review Link