We've recently cleared an area of weeds in our garden, but made the cardinal weeding sin of not replanting and leaving a 'weed shaped hole' in the garden. Having learnt this term, thanks to the Parliamentary Commissioner for the Environment, Simon Upton, I really should have known better!
So last night, I needed to plant some pumpkin seedlings I'd been given, which lead to needing to clear the weedy vines that had recently sprung up in this area. Greater bindweed (Calystegia silvatica) grows very rapidly and has taken over areas of my garden - including smothering the rat trap! It produces strong vines and flowers from October to May. Successful removal completed, hopefully we'll soon have lots of lovely pumpkins!
Greater bindweed has large, arrow-shaped leaves with distinct notches at the base and are arranged alternately along the stems. The leaves usually die back during winter. It has thick roots that can spread out over wide distances, helping it spread easily. It scrambles up and over other plants and out-competes them by smothering. It effects not just our home gardens, but also affects the survival of native species on streambanks, forest margins and in wetlands.
Of course, this particular 'weed shaped hole' was created by removing another pest weed, ivy! There are several invasive vines we find commonly in Aotearoa including several that are closely related to Greater bindweed, such as blue morning glory (Ipomoea indica) with blue flowers and purple morning glory (watch out for this one - it is currently only found in Napier, Christchurch and one site in Bay of Plenty).
There are several other bindweeds in NZ including field bindweed (Convolvulus arvensis) and pink bindweed or convolvulus (Calystegia sepium) which has extensive rhizomes (underground spreading stems), arrow-shaped leaves, flowers pink with white stripes, and is very common.
Two other similar vines are shore bindweed (Calystegia soldanella) which is usually just grows along the ground (not climbing), has smaller, thick, semi-succulent leaves, small pink flowers, and is coastal, and Calystegia tuguriorum which has slender, much branched, climbing stems, roundish or kidney-shaped leaves, flowers white or pink and grows in lowland forest margins all over New Zealand.
Control of these sort of vines is hard - sprays can have an effect, but will likely also impact desirable plants as they kill anything they come in contact with and spreads easily on the slightest breeze. Removal of as much as possible and suppression to give other plants a chance to establish is time consuming and will need regular attention, but is the most recommended control method (note to self - get planting!)
If you are keen to include vines in your garden, there other species that are not invasive and even some native options - try looking for NZ bindweed (Calystegia tuguriorum) , Scrambling fuchsia (Fuchsia perscandens) or Evergreen clematis (Clematis armandii).
Evergreen clemantis, Credit: Holders, iNaturalist.org NZ Bindweed, credit: John Barkla Climbing fuchsia, credit: Jeremy R. Rolfe
A final cautionary tale, that I'm learning by trial and error - many common garden plants, including ivy and greater bindweed can be irritants to the skin. I would recommend wearing gloves when removing this vine.