Japanese knotweed, giant hogweed and other invasive plants

If you do not manage invasive plants correctly, they will spread over time and they could cause damage to structures, such as building foundations.

If you have invasive plants on your site you should put up signs, where appropriate, to warn employees and the public about the invasive species that are present.

Put up posters in offices and communal areas to explain to employees what the problems are and what they need to do. Include pictures of the invasive plants you have on your site. This is particularly important for giant hogweed, as contact with sap from the plant can lead to skin burns.

Handling Japanese knotweed

Make sure your staff can identify Japanese knotweed rhizomes (underground root-like stems). This can reduce waste costs and improve how you manage Japanese knotweed on-site.

You should minimise the amount of soil containing Japanese knotweed material that you excavate. Soil containing Japanese knotweed material that has been treated can be reused for landscaping the site, but should not be taken off-site, unless to landfill.

You have a choice of herbicides that are effective against Japanese knotweed, depending on your situation - see spraying invasive plants with herbicides.

On development sites you should fence Japanese knotweed where possible, using clear signs so that only appropriately briefed personnel enter the enclosure to deal with the infestation and resulting waste. This includes areas with waste plant material or soil contaminated with Japanese knotweed. The fence should be at least seven metres away from the plants. Put up restricted access signs around these fenced areas. You must not use tracked vehicles within the affected area, and make sure any vehicles leaving the area are pressure washed.

You must never strim areas containing Japanese knotweed. If you are going to clear areas where Japanese knotweed is present, make sure you remove all cut stems - see disposing of invasive plants and contaminated soil off-site.

Do not try to compost Japanese knotweed material - it will produce new plants. You must not put cut plant material directly onto the ground. If you must stockpile cut material, make sure it does not come into contact with soil - for example, by placing it on top of a barrier membrane - see cutting and burning invasive plants.

Keep soil containing Japanese knotweed material separate from clean soil. This will reduce the volume of soil that you need to treat and dispose of.

Handling giant hogweed

When giant hogweed sap comes into contact with skin, it reacts with sunlight and causes chemical skin burns. Giant hogweed sap becomes more toxic as the year progresses and the plant is exposed to more sunlight.

The stem and underside of the leaves have hairs like a stinging nettle. Brushing against giant hogweed can be enough to get sap on your skin.

If you have giant hogweed on your premises, you must ensure that the public and your employees are protected from the hazards of its toxic sap.

You should control giant hogweed before it seeds. You must not use a strimmer on giant hogweed. The sap from the plant may get onto your skin or into your eyes.

If you are going to get close to or handle giant hogweed, you should wear full protective clothing with gloves, a hood and a full-face visor. You should wash down your protective clothing before you take it off.

If you get sap on your skin, cover it to keep it out of the sun. Go indoors immediately and wash the sap off your skin with soap and lots of water.