Tuesday, 14 October 2014

No great wine escape


Botanical colleague Neville Walsh was wondering, aloud, why you don't see grape vines taking over the Victorian bush. They grow well in many parts of the State, they produce plenty of fruit, and the seed-containing pomice from wine and juice making is often discarded outdoors. Yet there are only a handful of reports of its escape into natural vegetation.

Neville presumed, aloud, that the seed was most likely infertile. My extensive sleuthing on the internet supports this presumption, sort of. Growing grapes deliberately from seed it not easy. It can, according to one experienced grower, take up to three years. Firstly, only a small number of seeds will germinate. It may be that they are mostly infertile but also because they require 'stratification'.

That is the seeds need to be pretreated in some way before they germinate. Only by subjecting them to few months of cold temperatures to trigger the plant to force it's way through the tough seed coat.

According to this same source, Danie, once extracted from the fruit pulp, the seed need two to three months at just above freezing (1-3 degrees C). This alone would make most of Australia unsuitable for colonisation by a rogue grape.

Seed will still take a few weeks to germinate, and there are reports of it taking up to eight. Even after stratification the strike rate is low.

Other people simply recommend sowing the seed and then waiting for three months, presumably in places where temperatures drop a little and help the seed break its dormancy.



This is presumably why Vitus vinifera, the wine grape, is only 'sparingly naturalised' in Victoria. I notice that it's described as full-on naturalised (i.e. established and spreading in the bush) in Western Australia, South Australia and New South Wales (and 'doubtfully naturalised' in Australian Capital Territory).

That summary may over inflate the real situation given that in New South Wales, for example, the distribution based on vouchered (herbarium) records is 'occasionally naturalised' and there are only three records on the PlantBank database. How close these are to domesticated vines I don't know but the dots seem to be in established wine growing regions (e.g. Hunter Valley).

There are more dots (on the map) in Western Australia but mostly hugging around Perth with just a few in the Margaret River area. In South Australia there are 18 records, scattered around the south-west wine growing areas.

I don't get the impression it's a sleeper weed, with the potential to break out and rampage through our native vegetation. But if the climate changes to its advantage and we are careless in where we toss our pomice, who knows.

Images: The vineyard at the top is beautiful Tarrawarra in the Yarra Valley, where I saw no evidence of escaping wine vines. The other picture is of a single plant, one of the oldest and biggest in the world, growing inside at Hampton Court Palace and therefore unlikely to escape.

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