Japanese knotweed, giant hogweed and other invasive plants

Cutting down or digging up invasive plants and burning the waste plant material can be a useful, low-tech means of control. It can reduce the volume of waste that you need to dispose of off site.

Cutting invasive plants

Cutting Japanese knotweed will, over time, weaken the plant, but it will not kill the rhizomes (underground root-like stems). It can be used as part of other control practices. You must handle and dispose of cut plant material carefully. Burning alone may not be sufficient to kill the plant material. You should place burnt material on top of a membrane and monitor it for regrowth. You must not use a strimmer on Japanese knotweed.

Cutting giant hogweed before the plants flower will help to prevent further seeds being deposited on the ground. This is an effective way of removing these species but it can take many years. You must not use a strimmer on giant hogweed. You must avoid contact with giant hogweed, particularly its sap, as it can cause chemical skin burns. You should wear full protective clothing when working near it or handling it.

Pulling up Himalayan balsam before the plants flower is the most effective method of control. Do not cut the plants before they flower as this can result in a more bushy plant that produces more flowers. The best time to cut is late May. Cut the plant below the first nodule.

Burning invasive plants

If you burn waste in the open, you may require a waste management licence or exemption.

You may qualify for a paragraph 30 exemption to burn certain waste plant tissue and untreated wood if you:

• burn the waste at the place where it was produced
• burn no more than 10 tonnes in a 24-hour period

If you have an exemption, you must comply with the exemption conditions and register this exemption with the Northern Ireland Environment Agency (NIEA).

You must also ensure that your activity does not:

• endanger human health or cause pollution to water, air or soil
• constitute a risk to plants or animals
• cause a nuisance, eg in terms of noise or odour
• adversely affect the countryside or places of special interest

You must notify the NIEA at least a week before you intend burning plant material. You should also notify your district council environmental health officer before you begin burning plant material.

If you burn waste in an incinerator or other similar plant, you may need a pollution prevention and control permit - see burning waste.

Good practice for burning invasive plants

Burning plant material should only give rise to white smoke.

Tell the local fire brigade before you begin burning and again when you finish, so that they are not called out unnecessarily.

You can leave cut stems to dry out in the sun rather than burning them. Make sure you place cut Japanese knotweed and Himalayan balsam material on a membrane and not in direct contact with the ground.

Giant hogweed sap remains toxic after the plant has been cut down. Do not leave cut stems where they could harm people or livestock.