PENNISETUM - Friend and Foe

By Admin on 20-07-2015

Pennisetum are warm-season grasses that are native to many parts of the world, including Australia. Pennisetum range in form from grasses suitable for lawns ie Kikuyu (Pennisetum clandestinum) to medium/large tussocks that have been used as garden plants. The Australian species is Pennisetum alopecuroides and it is a tussock form and makes an ideal garden plant. Gardeners Planthub sells a number of popular cultivars of Pennisetum alopecuroides. We also sell one species from Africa. Let’s call these species Friends.

Now for the Foe. Pennisetum setaceum, (sometimes called Foxtail Grass or Fountain Grass), is from South Africa and south-west Asia. It is highly invasive and will germinate readily in gardens, bushland, even cracks in the footpath. Not the sort of plant you want to have around! Pennisetum setaceum has been declared a Class 5 weed in NSW (restricted weed which must not be sold, bought or knowingly distributed throughout the entire state) and Class 3 weed in Qld (environmental weed). As of the writing of this article, it is yet to be classified in other states.

 

Native Pennisetums safe to use in gardening and sold online through The Plant Hub website

· Nafray® - Pennisetum alopecuroides ‘PA300’

·· PennstripeTM - Pennisetum alopecuroides ‘PAV300

· Cream LeaTM - Pennisetum alopecuroides

· Pennisetum alopecuroides (common form)


Pennisetum alopecuroides is commonly called Swamp Foxtail Grass. Its distribution ranges from tropical Queensland to the south of New South Wales mainly along the coast. It naturally occurs in moist conditions and boggy areas. Importantly, Harden (1993) classifies Pennisetum alopecuroides as a native Australian species, however, to confuse the issue, many sources indicate it may not be indigenous to Australia, but rather naturalised having been transported here prior to European settlement.

Pennisetum varieties flower in late summer and autumn. Unfortunately, it follows that in areas with warm moist winters, such as tropical Qld and northern NSW, cultivars such as Nafray have been known to occasionally self-seed. We at Gardeners Planthub believe in responsible gardening and would not recommend growing this cultivar in such areas. To complicate things further, modern gardeners and landscapers will need to consider global warming and the resulting warmer winters some of us are already experiencing when using any plant that could self-seed. The same can be said of gardens with warm winter micro-climates, coastal gardens and irrigated gardens.

When grown in other areas, an uncharacteristically warm and moist winter can see some self-seeding. In this case, we recommend thick, quality mulch and vigilance. Beware of coarse mulch such as pine bark as this leaves gaps and exposed soil suitable for seed germination. Seed heads can be removed before the seed is set and unwanted seedlings can be treated very effectively with glyphosate.

In our experience, ‘Pennstripe’ is yet to produce viable seed. It is also the first variegated Australian native grass available. ‘Cream Lea’ has also proven to be non-invasive. There are no reports from customers of ‘Cream Lea’ self-seeding.

Pennisetum ‘Rubrum’ and 'Rubrum Dwarf'

Pennisetum ‘Rubrum’ is a commonly grown ornamental cultivar grown from the species Pennisetum advena native to Africa, the Middle East and East Asia. Both tall and dwarf forms are available. It is completely sterile and does not have a rhizome, therefore not become a weed.

Our Foe Pennisetum setaceum

P. setaceum is also called Fountain Grass. In an ideal world, setaceum would not be available for sale in Australia. Over the past few years, we have seen this plant for sale by unsuspecting retailers thinking it was the Native variety. The take-home message here is to be sure you/your contractor source plants from a reliable supplier. If in doubt, ask. Beware of plants produced by ‘backyard growers’ and sold at places like local markets.

Pennisetum setaceum flowers most of the year and produces an abundance of viable seed, which is mainly dispersed by wind but can also be spread by vehicles, humans, livestock, water and possibly birds. Where the native form has 10 – 30% seed viability, setaceum has close on 100%. Notably, the seed has been reported to remain viable for up to 7 years. It was likely brought into Australia as an ornamental grass and has been living it up here ever since.

According to the NSW Department of Primary Industries, P. setaceum is difficult to eliminate. Control may need to be repeated several times a year. The long-lived seeds mean continued monitoring aft­er treatment is essential. Control should initially be directed to outlying populations followed by treatment of the core area. Small infestations of fountain grass can be removed by uprooting and removing/destroying seed heads. Extensive infestations of fountain grass are probably best controlled with herbicides, combined with mechanical techniques.

The invasive behaviour of setaceum is likely to be the first step in its identification. Other features include:

· upright tufted grass with very narrow leaves and flowering stems growing up to 1 m or taller

· long spike-like seed-head (6-30 cm long) are reddish, pinkish or purplish in colour

· flowers are always present

· Pennisetum setaceum has a hairy peduncle (flower stalk) compared with the hairless peduncle of our native one's flower.

· Seed-head contain large numbers of densely packed stalkless flower spikelet clusters

· each flower spikelet cluster is surrounded by numerous feathery bristles (12-26 mm long) and one significantly larger bristle (16-40 mm long)

· its mature seed-heads turn straw-coloured or whitish and the seeds are shed with the feathery bristles still surrounding them.

If in doubt about identification, contact your local council or post a specimen to your nearest botanic gardens (most botanic gardens have a plant identification service that charges a small fee).

 

REFERENCES

Harden, G. J. (Ed) 1993 ‘Flora of New South Wales Volume 4’ Copywrite Royal Botanic Gardens and Domain Trust. Published by New South Wales University Press, Kensington, NSW Australia.

NSW Primary Industries Biosecurity (part of Department of Primary Industries) Weed Alert Brochurehttp://www.dpi.nsw.gov.au/agriculture/pests-weeds/weeds/profiles/fountain-grass

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