Invasive Species

All of these species are non native to Britain and can cause problems if not kept under control, for each species I have put a summary of why it is a problem, the harm it does and the preferred method of control. For each of these species FoHW will be liaising with the Conservation Officer to agree how to control it. All these photos were taken in Ham Woods.

Most of these species are garden escapees, it is vitally important that garden waste is not fly tipped in the woods.

Japanese Knotweed

This is the top of everyone's nasty plants list. It is only spread by humans as the seeds in the UK are infertile. This means we only have ourselves to blame when this plant appears and starts putting out roots. It grows at a phenomenal rate and will lift concrete, brickwork and buildings. Just a small piece the size of a head of a match is enough to spread it. It is an offence to release or spread this plant in the wild, any plant material, or the soil it is growing in MUST NOT be put into the recycling waste, indeed, knotweed plant material and the soil it grows in can only be moved if it is handled like hazardous waste by an approved and registered waste disposal company. You are allowed to bury it on site but it must be covered with an impermeable membrane and be at least 5 meters deep! We have discovered areas of Knotweed behind Ham House.

Preferred method of control is chemical spray, if this is not possible, each shoot has to be injected with a herbicide.

Himalayan Balsam

This is an annual plant (grows from seed each year). It produces pink / purple flowers towards the end of July which look pretty on there own. Don't be deceived! This plant out grows any other annual and can grow up to 3m tall (10 feet). It crowds out the native ground cover and when it dies back in Autumn the ground is left bare over Winter and is subject to erosion. The seeds can last for two years. The preferred method of control for this species is to uproot it (or break the stem) before it sets seed (known as a Balsam Bash). The seeds are ejected from the seed pod when ripe and can be thrown 7 meters. It also spreads by water and this year (2012) it is present along the whole length of Ham Brook, but not in the stream down from Ham Drive.

Seedling with cotyledons and with adult leaves emerging.

Flowering Himilayan Balsam (23rd July 2012), these flowers are pale but they can vary from this pale pink to deep purple.

Once the plants get to this stage they will need to be removed immediately to stop them setting seed.

Cherry Laurel

Used in gardens as a hedging plant, when cut regularly it causes few problems. When not cut it grows into a large shrub or tree, at around 10 years old, it starts flowering producing cherry like fruits in Autumn which spreads the seeds by birds. This plant damages the woodland undergrowth by it's dense canopy which shades out ground plants. Cherry Laurel also produces cyanide compounds to protect itself against insect attack, due to these compounds, removal and disposal of Cherry Laurel needs to carefully planned. Control of this plant is physical removal followed by chemical treatment of the stumps to kill them. During Autumn / Winter 2011/2012 we have done a considerable amount of work to get this species under control, but there are several more years of control work required. As there are mature fruiting Cherry Laurel trees in gardens around the woods and in Weston Mill Cemetery we will need to continuously monitor this species.

Non Native Bluebells

Until recently, Bluebells bought for gardens were all of the larger more aggressive Spanish variety. The native English Bluebells are now available for gardens. The problem with the Spanish Bluebell is that it hybridises with the native English Bluebell, hybrids generally show the dominant Spanish characteristics. Control is by digging up the plants when in flower. The march of the Spanish bluebell has affected many English Bluebell woods but as we are situated in a location surrounded by gardens, the problem for us is particularly acute. Although most prevalent around the edges of the woods, the Spanish Bluebell can be found all over the woods. We are producing a separate document to identify English and non native Bluebells, but one of the charicteristics of the English Bluebell is it's powerful fragrance - unmistakable when the English Bluebells are in full bloom in May. The Spanish Bluebell has no scent.

Winter Heliotrope

Easily identified by it's large round leaves, this plant flowers in Winter with highly fragrant flowers. Only the male plant is present in the UK so it spreads by propagation alone. The large round leaves blocks out light and smoothers other plants. As it spreads, large areas are covered by it's round leaves. Control is best using chemical herbicide as digging or pull up the plants leave fragments which regrow.

Variegated yellow Archangel (yellow Deadnettle)

Another garden escapee. This plant is popular for hanging baskets and is spread to the woods when garden waste containing hanging baskets are fly tipped in the wood. In gardens, this plant is also used as ground cover and it performs these duty effectively in the woods, smothering out native ground cover plants. The preferred control method is sheet mulching, chemical spraying is possible but care is needed to prevent collateral damage. The main areas of Archangel are at the back of Fountains Crescent but there are other isolated areas around the woods. This plant spreads by both vegetative propagation and by setting viable seeds. Thankfully, it is not too aggressive in it's spread. The non variegated plant in native and not invasive.

Primula (primrose family)

The Primrose is the County flower of Devon and is sadly not at all common in the woods. Where it does exist, there is evidence that it has hybridised with garden primula (similar flowers but many flowers on one stalk). This results in primrose looking flowers but of differing colours from the pale yellow of the native Primrose. Typically these hybrids are pink or purple and this is the main method of identifying these plants. Control is by digging up individual plants.


This garden escapee forms distinctive orange flowers and has reed like stems. It has taken hold along Ham Brook. It spreads mainly vegatatively but is able to set viable seeds. The main method of control is to pull up the corms but as small parts invariably remain further control is needed in subsequent years.

Three Cornered Leak

Looking like white bluebells, this plant spreads aggressively. It has a garlic smell and can be eaten in place of Garlic! It is easy to recognise as the flower stalks have a triangular cross section. Control is by continuous mowing or digging up the plants when in flower. It spreads mainly by seed but also by division of it's bulbs. There are one or two plants dotted around the woods and a larger area on the grass slope at the bottom of Fountain Crescent.


This popular garden hedge plant has red berries that are favourites for birds, it is spread by seed and in some locations has become so extensive that it excludes native species. In Ham Woods there are currently (2012) only a few plants. These should be controlled by cutting back / uprooting. More aggresive control may be required if Cotoneaster becomes more prevalent. This species is to be monitored closely.


This tree was introduced to Britain by the Celts and then reintroduced by the Normans and could be considered as one of our native species. In mature woodlands with full canopy cover the shade is such that the saplings do not get enough light to compete with other saplings. Wherever there is a break in canopy cover Sycamore can thrive and appear to be an invasive species. Current thinking is to concentrate on providing good canopy cover and the Sycamore will not be a problem species. In Ham Woods, we are not in a position to ensure the full canopy cover and as a result we may need to control sycamore in isolated localised areas. The Sycamore produces vast numbers of winged seeds and in April, Sycamore seedlings appear everywhere.

Leyland Cypress

Famous for being the hedge of choice for the Neighbour from Hell, this is a very rapidly growing evergreen tree. It is present around the Industrial Estate with a few species in the woods. As this species does not set seed, it does not spread. It is not considered a problem in the woods.

Bay Laurel

The Bay Laurel is the source of the Laurel wreaths used as prizes in the Ancient Olympic games. It produces viable seeds but very few of these germinate and as such this tree spreads only slowly. This evergreen tree is a true Laurel and does not produce the same cyanide compounds as Cherry Laurel (which is part of the almond, cherry, plum family). It's main effect on the wood is the shading of the ground cover but this is not generally as thick as Cherry Laurel. Control is physical removal which should be sufficient to kill the tree. As it is slow spreading and does not affect the ground cover too badly this is a low priority species to control

Other non native shrubs (mainly garden escapees)

Many garden shrubs escape to invade the wood, these include Berberus, Bamboo and various evergreens. Most of these do not spread aggressively and have minimal impact on the wood. They need to be monitored and appropriate action taken.