A fortnightly series first published in the Weekend Gardener and reproduced here with their permission.
We are very cautious about invasive plants here. I know there is an old cliché that says a weed is just a plant in the wrong place but in a large garden, we can’t afford to have out of control triffids. If a plant starts to look dangerous, it probably is. If it is a prolific seeder and the seed is dispersed by birds, it is even more problematic. The campanulata cherries fall into this category and if it weren’t for the scores of tui they attract to the garden each spring, we would do away with them. The seeding bangalow palm (Archontophoenix cunninghamiana) is also a source of angst. The same goes for the Himalayan Daphne bholua which doesn’t just seed. It also suckers below ground. If we lived near a national park or adjacent to a native reserve, we would feel morally obliged to review our hospitality to these ornamental plants.
We are nowhere near as tolerant of wayward perennials and annuals. Forget-me-not may be pretty but it is aptly named. We have been weeding it out for years here and still it stages a comeback. The orangeberry (Rubus pentalobus) had to go when it formed an impenetrable mat after just one year then started climbing and leaping to extend its territory – but never fruited. Some of the ornamental tradescantias (wandering willies) are also invasive. We have a very pretty blue flowered form but it sets prodigious quantities of seed and is popping up in thickets many metres away. The remains of the arum lily Green Goddess still require regular attention to get rid of the last remnants of tiny rhizomes out of the ground.
Where we have plants which set miles too much seed, like the granny bonnets (aquilegias) and the sweet williams (dianthus), we try and deadhead straight into a bucket. From there, they either go to the bottom of a hot compost heap, out with the rubbish or on the burning heap. Composting alone does not kill seeds unless you manage your compost in a way that generates considerable heat. While we don’t mind a certain amount of seeding down of pretty plants, we like to keep them confined to particular areas and don’t want to spread them everywhere when we use the compost as mulch.
1) Persuade Mark to head out with the chainsaw and cut down some of the self seeded pongas. We don’t regard these as weeds because they are native, but we end up with too many of them. We have them as raised beds in the rimu avenue, where some are now 50 years old. I want to extend the constructions along further and feature more bromeliads. I have never learned to use a chainsaw and am terrified of them. Mark is equally worried by what I could do with one if I became confident so has never encouraged me to learn.
2) Mark has been raising perennials from seed in the nursery and I need to get onto planting these out. I was particularly pleased to see a tray of eryngiums – blue sea holly. It is a little bit prickly but so very pretty. Blue flowers are my absolute favourite. It would have been better had we got onto planting these out earlier but they are perennial so should grow on to star next summer.