Sweet pea shrub
Sweet pea shrub Polygala myrtifolia is a South African import and a common weed in coastal areas of Northland.
Why sweet pea shrub is a problem
Sweet pea shrub is fast growing and tolerates a wide range of conditions. It shades out low-growing coastal native plants, and spreads through dunes. Adult shrubs don't live that long, but they produce a massive seed bank with long-lived seeds which makes this weed very hard to control.
Sweet pea shrub flowers
How you can identify sweet pea shrub
Sweet pea shrub is in flower late spring - early summer. You can see plenty of this weed on the Ngunguru river mouth headland track and on the Ngunguru sandspit itself.
Look out for light green foliage and pretty 3-petalled purple and green sweet-pea like flowers.
Sweet pea shrub has a close but non-weedy relation that is often found in gardens. The way to tell them apart is that the weedy one has a green surface to the outside of the outer petals, and the non-weedy one has entirely purple petals on both sides.
Looking at coastal sites like Ngunguru the widespread and successful nature of the plant confirms weediness without close identification.
Control of sweet pea shrub
Small plants can be pulled out and left to rot down. You need to cut down larger plants and spray or treat their stumps with herbicide to prevent regrowth.
An ecologically and culturally sensitive area such as the Ngunguru sandspit in Northland requires a special approach. Now this site is in public hands, pest management through a suitable plan, which would incorporate other weeds such as pines, pampas and sweet pea shrub, is likely.
How you can help stop the spread of sweet pea shrub
If you live near the coast anywhere in Northland, get rid of sweet pea shrub from your garden, and try some exciting alternatives such as tibouchinas with their bright purple flowers, or perennial salvias. For a native alternative, try manuka cultivars (Leptospermum scoparium).