Bed of Nettles

December 2024

If you want to attract butterflies, you need nectar flowers and you need food plants for their caterpillars. Lots of people know that swan plants bring monarch butterflies into the garden, but I'm not sure how many know that for red and yellow admirals, you need nettles.

An admiral caterpillar on nettles

New Zealand has native nettles. What I call the Chatham Island nettle, also known as Southern nettle, Urtica australis grows huge leaves in the right conditions. It's the main nettle for the Chatham Island red admiral. Urtica aspera, with a status of 'At risk - Naturally Uncommon', seems to be uncommon enough not to get a common name. It is found in the South Island and grows over 300m above sea level. Urtica perconfusa, also under threat, is a swamp nettle and is found from the mid-North Island south.

Found across most of the country is Bush nettle, Urtica sykesii, but it is not really found in the Auckland region. Last but not least is Ongaonga or Urtica ferox, which is the tree nettle which has killed a couple of people and is also found across most of the country bar Auckland and Northland. This is the main host plant for the mainland red admiral.

Now I've looked at nettle locations on iNaturalist, I am amazed that the admiral butterflies were reported as common around the Auckland region before the powers that be spent a decade aerial spraying for invasive moths. This may be because the admirals used the introduced nettles - the annual nettle Urtica urens and what I call a stinging nettle, being a European import myself, also called perennial nettle, Urtica dioica, which both naturalised in New Zealand about 1860-1870.

Urtica dioica is a banned plant in Auckland and the Hauraki Gulf and you are not allowed to propagate it or plant it. Because of that I did not dig some roots up from an overflowing clump in a local community garden and grow some in pots. They propagate so much more easily than the native nettles, being the thugs they are, but even in pots they can be spread by birds eating the seeds, so I would keep them close to the house, if I had any. Which I don't.

I really want to replace them with native nettles, but as I say, I am having difficulty growing the native varieties. My last attempt at growing Chatham Island nettle failed completely, but I did have some grow from seed back at the old house. I have never got bush nettle to grow from seed. The New Zealand Plant Conservation Network says bush nettle is really easy to propagate, which is just rubbing it in, really. I readily admit I am not the best at raising plants from seed, but I really should be able to raise something classified by most as a weed.

I managed to buy a small urtica sykesii a few years ago from Eden Garden, which has a nettle house and raises admirals. This did grow into a large pot, but I haven't managed to propagate it with cuttings. Now we have a big garden, I am going to plant this directly into the ground and it needs shady, moist soil. The Chatham Island nettles are also going to be planted and, whilst I can't find a reference, it looks like this species prefers full sun to part shade. It's not a fan of humidity and whilst the Chathams has a maritime climate, it doesn't get the same amount of sun as Auckland, so I'm going to plant them with tree cover to keep them cool and hopefully that will work. They survived down the side of the old house for a few years, so I think they will do okay.

Identifying the site is on the project plan:

7. Need to identify a damp, semi-shaded area and child-safe site for nettle field away from flower garden.

The problem I have is that the garden slopes and the only damp place in the warmer months is by the stream. Unfortunately I just can't get down there easily - imagine a mud version of rock-climbing - so I wouldn't be able to monitor the plants for caterpillars. However, I need to keep the nettles away from the flower garden. Apparently the perfume of the flowers can mask the scent of the nettles for butterflies looking to lay eggs. The nettle bed also needs to be away from the kids' play space.

This leaves the bush area at the very top of the garden. However, there are a couple of problems - a ton of debris, which makes it hard to move around and work up there, and ginger.

Dead and live ginger, as well as broken branches at the top of the garden

The ginger is going to be an ongoing problem and it is one of the dirty dozen list of invasive species. This isn't the stuff you can eat. This is the stuff that takes over forests.

I'll need to clear a good amount of space to make room for the nettle bed. The minimum recommendation for a nettle bed is four square metres, so the butterflies can find it. Hopefully the native nettles will grow to fill that kind of space without needing additional plants, as I seem incapable of providing them.

My idea is to turn all the debris into some dead hedges - a barrier made of branches, plant waste, etc - which will give room to plant and still give the wildlife that depend on rotting wood an undisturbed place to live. It would also stop the kids running into the nettle bed by accident (although it is very hard to walk up there, let alone run, it is so steep).

I missed the window to plant the nettles in spring, thanks to lomandra, so I will now wait for autumn to clear the ginger and plant the nettles. Hopefully there will also be less mosquitoes around. The garden is rife with them and every hour I'm working on it, I sacrifice blood. We need more piwakawaka and dragonflies to take them out!