SWEET PEA SHRUB Polygala myrtifolia
THIS IS AN OLD garden favourite that has escaped out the gate. It once held the status of being one of the most popular garden plants for its rapid growth and year-round blooming habit, but its hardy habits now make it a pest, particularly in Northland, Auckland, other parts (mainly coastal) of the North Island, and in the Nelson region.
Sweet pea shrub grows rapidly into a 2m (often higher), multi-branched, rounded, evergreen shrub. It is densely clothed in attractive, yet unremarkable, light green foliage. Young shoots have short, curly hairs.
Purple, pea-like flowers, with green outside petals, occur year-round, followed by flat, heart-shaped seed capsules containing hairy, dark brown seeds.
IT’S CONFESSION TIME. Sometimes I make mistakes. Admittedly it doesn’t happen very often, but it does happen.
Occasionally I misidentify a weed. I was given a description of it, I made a call and I fell into a trap for beginners, mixing up my lamiums. I called red dead nettle and it was actually henbit.
Red dead nettle ( Lamium purpureum) is an annual weed found pretty much all over New Zealand, generally in gardens and sometimes in cereal crops. It is a native of Central Europe and Asia, but has effectively spread throughout the world.
It’s a member of the mint family which includes such notables as mint, henbit, basil, oregano, thyme, and marjoram, which all sounds like the starting of a good pizza.
Lamium comes from the Greek word for throat which refers to the shape of the flowers, shaped a bit like an open throat. Purpureum is the Greek word for purple which refers to the colour of the flowers. In much of the rest of the world this is ‘purple dead nettle’ but I think red dead nettle sounds better.
The ‘dead nettle’ part of the name is interesting too. They do kind-of look like a nettle plant but without the sting, therefore it’s a ‘dead’ nettle. Get it?
As with nearly all members of the mint family, red dead nettle is completely edible. It tastes good in a salad or stir-fry and the flowers are sweet.
Identifying it is usually easy (stop judging me!) but it does look very similar to a number of other weeds, and if they aren’t side by side it can be easy to mistake it. It grows to around 20cm high and can germinate at any time during the year. It produces a number of small stemmed, serrated-edged leaves that are green at the bottom of the plant and slightly purple colour at the top of the plant. This is similar to henbit leaves but the key difference is henbit leaves don’t have a leaf stalk.
At the top of the stem, the plant produces a large number of pretty little purple flowers. This can be a mixed bag. Get it early and it’s easy. Get it late and it’s impossible.
Keep your crop or garden happy, healthy and competitive and you’ll stop it from getting a toehold. You can easily pull it out by hand and that’s always worked well for me.
On a large scale, most of the usual suspect chemical options don’t have any effect. You can use Bromoxynil in cereal crops, but beyond that there isn’t much else.