Threatening Weeds

Garden Plants can ‘jump’ the garden fence, and invade the local bush.

It has been known for 15 or more years that some Garden Plants can ‘jump the fence’, ‘go bush’ and become environmental weeds. These plants may ‘escape’ because they are dumped or are spread by means that take them beyond the garden fence. About 32,000 species of plants have been introduced into Australia; of these 8% or 2,100 are known environmental weeds. The direct cost of weeds to just the agricultural industry is estimated to be $3.3 billion a year – this is without the cost to the environment and biodiversity1. The 2001 State of the Environment Report states that 65% of Australian environmental weeds are garden escapees.

There is no ‘legal definition’ of an environmental weed however the “Flora and Fauna Guarantee Strategy: Conservation of Victoria’s Biodiversity” uses Geoff Carr’s 1988 definitions of an Environmental Weed viz. “Environmental weeds are naturalised non-indigenous plant species which adversely affect the survival or regeneration of indigenous species in natural or partly natural communities.” Dr. Graeme Lorimer, author of various bush reserves’ Management Plans, and the main author of the “Study of Sites of Biological Significance in Maroondah” defines an Environmental weed as “A plant that does not occur naturally in a particular area of vegetation and that is having an adverse effect on species of flora and/or fauna that do occur naturally in that area. These adverse effects could be through displacement, competition for resources, toxic effects or prevention of the natural flora or fauna from re-establishing in the area”. As well as grasses and ground covers, environmental weeds include bushes and even tree species.

Garden Plants can become Environmental Weeds because they can survive without attention including watering – these are just the properties that appeal to a busy gardener especially at times when people are looking for drought tolerant species. The Sustainable Gardens Australia’s electronic Newsletters of Nov ’04 says “Sometimes the very same things that make environmental weeds so aggressive are the very things that we desire in our garden plants – they’re virtually indestructible, with lots of flowers, and they spread around the garden to fill in bare patches.”

Plants can spread by

·The seed being blown by wind eg Desert Ash (Fraxinus angustifolia subsp. Angustifolia),

·Storm water washing away piece of the plant which eventually stick in the sides of gutters, creeks or rivers, eg Pussy-willow (Salix X reichardtii),

·Storm water washing away seed eg Common Violet (Viola odorata),

·Birds eating the fleshy fruits of the plant and defecating up to 2 km away eg Western Australian Bluebell Creeper (Sollya heterophylla), and Sweet Pittosporum (Pittosporum undulatum),

·Animal eating the fruit or seeds and defecating later eg Cherry-plum (Prunus cerasifera),

·Ants carrying wattle seed to their nests – up to about 75m away eg Sallow Wattle (Acacia longifolia),

·Seed pods bursting & spreading seed up to 2m away eg Broom (English Broom – Cytisus scoparius or Cape Broom Genista monspessulana),

·Sticky Seeds sticking to animal’s fur and human’s clothes eg Wood Forget-me-nots (Myosotis sylvatica),

·Ground covers creeping into neighbouring properties eg Wandering Jew (Tradescantia albiflora),

·Dumping of garden rubbish – almost any plant that sets and grows from seed, has bulbs or corms (eg freesia), or reproduces vegetatively.

If a plant in a garden is able to spread by itself eg by runners or seed, that is an indication that it is or could become and environmental weed.

Any plant which can regenerate from plant pieces eg willow, should never be planted where pieces that break off can be washed into the drainage/creek system.

Plants which set seed and are grown for their foliage or flowers such as agapanthus (Agapanthus praecox subsp. Orientalis) have the potential to become an environmental weed, but the gardener may still decide to grow the plant but cut-off the flower heads after the petals have fallen, but before the seeds develop. It is also better for such species to be planted only in positions where the seed cannot be washed into neighbouring properties, or the gutters and hence the creeks.

However some plants are grown for their attractive seed heads. One such plant is Tufted Fountain-grass (Pennesetum setaceum) which has become a popular garden plant, but because it is spread by the wind, gardeners cannot grow it for its seed head and prevent it from spreading, so gardeners are urged to choose an indigenous (local native) grass instead.

Similarly, many gardeners like to grow plants with berries to attract the birds, but the birds spread the seeds far and wide, and again gardeners should consider planting indigenous species instead.

Many plants can in fact be spread by more than one method. As we have seen some of these methods of spreading can be controlled by the gardener but others are much harder to stop. So a plants such as English Ivy (Hedera helix), which initially creeps into adjacent areas, and then when it reaches a wall or similar will climb, and in time produce berries which are very attractive to birds, could be grown provided that the gardener is prepared to prevent it from creeping too far and from climbing.

Dr McFadyen of the Weed CRC reports that a biological control has now been found for Bridal Creeper but that has taken 10 years of scientific effort and a million dollars! So obviously prevention is better than eradication.

Grasses are often the hardest environmental weeds to remove from a bush area. What is true for plants which are usually planted in flower beds, is also true for grasses. So when caring for a lawn, mow it before the plants produce seed; and if the species of grass spreads by rhizomes, make sure you contain the grasses within you lawn area.

So what can the aware gardener do?

·Plant an indigenous species instead. A garden plants which is an environmental weeds can usually be replaced by an indigenous species of similar form which require similar sun and moisture conditions – see(iv) below. Indigenous plants can be purchased from CRISP or Candlebark Nurseries – see below.

·Be careful when buying an exotic (non-indigenous) plant, being particularly careful if buying a plant or seed by mail order or ‘on-line’. If you buy from a nursery which is accredited by Sustainable Gardens Australia, the nursery will not sell known environmental weeds or at least will have a warning label on such plants.

·Buy infertile plants.

·Consider how a particular plant spreads; whether it is ‘safe’ to plant it; and if measures should be taken to stop it spreading, to actually carry out those measures.

·Never dump garden refuse including grass clippings.

Hopefully as gardeners become more aware, we can reduce the spread of environmental weeds, and the bush and biodiversity can flourish AND gardeners can still have easier to care for plants which also need less water.

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Possible indigenous replacement species for the plants mentioned above

Grasses with attractive seed head – Kangaroo Grass (Themeda triandra)

Bushes with fruit for birds – the Prickly Currant Bush (Coprosma quadrifida).

Plants with attractive flower heads – Flax Lily (Dianella sp) – a suitable replacement for Agapanthus.

Climbers – Wonga Vine (Pandorea pandorana) and Mountain Clematis (Clematis aristata)

Ground covers – Kidney Weed (Dichondra repens).

For further species see (iv) below.

References

1)Weeds and Pests: eradicating the invasive threat. Position Paper WWF Australia Jan 2003

2)Media release by Dr. Ruth McFadyen of the CRC for Weeds.

3)Sustainable Gardens Australia Electronic Newsletters – phone 9850‑8165 or visit www.sgaonline.org.au for a list of certified nurseries. SGA also has a free monthly emailed newsletter.

4)Plants of Melbourne’s Outer East – Indigenous and Environmental Weeds (and how to remove the weeds) with text and photos by Helen Moss Dip. Hort. Sc. Produced by Baber Enterprises P/L

5)Bush Invaders of South East Australia by Adam Muyt

More information about Environmental Weeds

i.Leaflet/ poster “Hochkins Ridge Flora Reserve – Wild Flowers in the City” which shows indigenous plants on one side and environmental weeds on the other

ii.Manningham Council’s booklet “Weed Identification”

iii.Banyule Council’s Leaflet/ Poster “Environmental Weeds” – this only includes possible garden plants and gives suggested indigenous (local native) replacements and

iv.A ‘sheet’ listing Garden Plants which can become Environmental Weeds and possible indigenous replacements with a similar form and growing conditions. The ‘sheet’ was produced for Maroondah Bushlinks by Helen Moss, Dip Hort. Sc.

i. can be obtained from Maroondah City Council Offices & Libraries

& (iv) can be obtained by contacting Maroondah Bushlinks Ph 9876-3094 or email MarBushOz@hotmail.com

Indigenous Nurseries

CRISP Nursery located at Greenwood Ave Ringwood (near Jubilee Park)

Wed & Fridays mornings 9.30am-12.30pm

March to October Open 1st & 3rd

Saturdays 10.00am to 1.00pm

Phone 9879-3911

Fax 9879-1161 or

email crisp@melbpc.org.au

Candlebark Nursery Hull Rd Mooroolbark cnr Hull Rd & Taylor Rd

Every Sundays-Thursday 9.00am to 4.00pm

Phone & Fax 9727-0594, or email info@candlebark.org.au

If you live in, or near, a bush area, tell the nursery where you live and ask for plants with the correct provenance.