This article was published in the Titirangi Tatler, October 2011
Last month's article about the rare vine from the Three Kings Islands, Tecomanthe speciosa, set me thinking about other vines and how they so often become weeds because of their vigour and natural instinct to overwhelm whatever they are growing over. In Auckland we are fortunate not to have a major problem with the exotic ‘Old Man's Beard' or Clematis vitalba. Further south it really demonstrates the smothering effect vines can have, where it overtops tall kahikatea and rimu trees to the point where the trees are killed from lack of light. The native Clematis species do not cause the same overpowering effect. A native climber that has a bad reputation is bush lawyer or Rubus cissoides. Its clinging thorns that grab as you tramp through the bush are so painful, but the vine produces beautiful cascades of spring flowers and is a good source of food for birds. We just have to accept there are some difficult things in life we need to appreciate for the good they do. We should learn to love bush lawyer as it serves a useful purpose in nature's scheme of things.
Here in the Waitakeres we have our share of invasive vines and it is difficult to choose the worst one. In home gardens it is generally the neighbours' beautiful jasmine vine that smells so sweetly which causes the greatest trouble. Layering as it travels unseen across the ground, it is well anchored with roots at every node, and strenuously resists removal when pulled out. Under tension, each root tears a portion of bark from the vine's stem, retaining sufficient material to start a new plant from every node. So instead of eradicating the plant by simply pulling it out, you have propagated dozens of individual plants already well-rooted into the ground. Do not confuse this invasive plant with the unrelated native species Parsonsia heterophylla, sometimes erroneously called native jasmine.
The vine that so often defeats restoration efforts is known as bindweed, morning glory or Convolvulus. This is seasonal and grows rampantly from October throughout spring and summer before dwindling in autumn and totally disappearing in winter. Disappearing does NOT mean dying as the underground stems have built up food reserves and lie dormant before spreading further, much further, underground to come up metres away from where they appeared last year. An interesting characteristic of the plant is that in spring the new growth is so strongly drawn to light the vine spirals upwards, but in autumn it becomes light averse and drops straight to the ground from treetops in order to reroot and prepare for winter. There is a related native species called Ipomoea cairica which is beautiful and relatively uncommon, but it can be just as invasive in the garden, so be warned! It is a Pacific-wide species and is known as ‘mile-a-minute' vine in some places or ivy-leafed morning glory. Here in Auckland the ‘mile-a-minute' vine generally refers to the invasive South African vine Dipogon lignosus which is in the legume or pea family.
Common names are often confusing and ‘ivy-leafed morning glory' does not mean the plant belongs to the ivy family. But talking of ivy, I have an area where I am attempting to recreate a grass understory of Microlaena stipoides below a canopy of native trees. Having assiduously sprayed and hand-weeded the pest plants for several years I felt I was on top of them, even the convolvulus which reappeared in one spot last summer. Now it is spring and the birds have obviously been active importing weed seeds as I have recently pulled out 200 - 300 germinating ivy seedlings with their first leaves just developing. Still they come and it becomes increasingly difficult to see them amongst the thick grass sward. Eternal vigilance is the price of freedom from weeds. Perhaps the most persistent weed I have encountered is the exquisitely beautiful wisteria vine that has defeated me for over 20 years. No matter how much herbicide I spray on it or how many times I dig it out, it reappears from the same root stock after an absence of a year or two.
I guess I am not going to win the weed battle until all my neighbours take up the same fight against the same weeds. Of course many people like ivy while others enjoy weeds such as ginger and Mexican daisy. It is unfortunate that plants so attractive in the home garden can become so destructive of our native vegetation over a period of time.
Most home owners will have seen the booklets various organisations have produced giving advice on which plants to avoid, and what to plant instead. If you need assistance, the Auckland Council website has lots of information to help you avoid planting species you will one day regard as a weed, and to eradicate those weeds you already have.