Verbena incompta and V. linearis as "Benign exotic herbs" for Gahnia Grove

[UPDATE April 2021:
Both species were reduced and suppressed, but regrowth of both was subsequently retained in some places where alternate ground cover was not yet established and the need for shade was high.]

V. incompta has proved an excellent shade to 2-3mH, remaining green longer through summer drought on this dry ridge-top than any other shrubby herb species including totatoa and Senecio eslierii.]

Both these species germinated with great abundance and density thorughout the bared clay banks, and grew to provide essential shade and shelter for these bared areas during Summer and Autumn. We expected to see them develop as tall single stemmed annuals, allowing other plants to grow beneath them as we recalled having in 1999 seen "Purple top", believed to be Verbena bonariensis, along Kaipatiki Roadside, where it was easy to knock down once mature.

Whether the incompta we have had identified here is the same species or not, in the conditions of a dry poor-soil ridge from which competing kikuyu and shrub weeds had been eradicated and native plants were not yet present, neither of these species showed any sign of yielding to old age by mid-August, and between the two of them they had achieved dominance over most of the area, with wild carrot and ox-tongue becoming scarce.

Both these Verbena species are known to be extremely tolerant of arid soils, and both developed many spreading stems from thick long woody roots at ground level.

So we decided it was time to remove them while they can still be composted usefully before Spring germination of both native plants and less-aggressive exotic herbs.

Few could be uprooted, and cutting stems low often leaves a large root mass on the surface, so we have broken most plants down over themselves, cutting the thickest (ie 8-10mm) stems as low as possible, and covered all roots and stem bases with their softer upper stems and foliage.

Hopefully most will weaken and be able to be uprooted. If not, this task will be ongoing for the coming year at least, unless enough mulch to suppress them can be produced from Spring growth of ox-tongue, wild carrot, Black nightshade and anything else leafy.

In either case, we expect to have to mulch a lot of Verbena seedlings this year.

These plants were difficult to uproot even as small seedlings. So though their welcome growth provided quick low shade, moisture retention and, when rains came at last, erosion control, in the conditions this year at Gahnia Grove we might have better advanced benign plant cover and the transition to native vegetation by mulching over most of them as seedlings.

But it is impossible to be sure, as without their hardiness through summer, the drought might have had even more impact on the existing native vegetation and the growth of benign exotics.

Posted on August 15, 2019 07:42 AM by kaipatiki_naturewatch