Pasture weed watch
A tiny invader turned tyrant
The sky is clear, the birds are singing and it’s around 15°C. I should be happy, but all I can see is the state of my lawn.
One of the benefits of living in Invercargill (there are many) is that for four to five months of the year, I don’t have to worry about cutting the lawn. It just doesn’t grow.
Well, it shouldn’t grow, yet there it is looking long and scraggly. To make matters worse, there is a damp end to my lawn where the grass is being out-competed and replaced by a truly annoying weed. In honour of my scruffy lawn, let’s talk about hydrocotyle.
When we are talking about hydrocotyle we are actually referring to one of 10 different species found in New Zealand and nearly 100 around the world. They are all very similar in appearance and function - I can’t tell them apart - so let’s just treat them as one for the sake of this column.
Hydrocotyle are found all over New Zealand; wherever there is excess moisture, they will be there. They like it so much, some botanists actually classify them as an aquatic or semi-aquatic plant. Hydrocotyle are one of the few plants that can happily grow in continually wet or waterlogged soils and they tend to colonise it very quickly.
The botanists are also in a bit of debate as to which family of plants Hydrocotyle belongs too. For a long time it was thought to be in the Apiaceae or carrot family, but recent genetic analysis has put Hydrocotyle into the Araliaceae or ivy family. Both of these families of plants are quite inter-related so in my opinion it’s a bit of a moot point.
Hydrocotyle is one of the few weeds I have come across that has no other uses. If anyone does know more, drop me a note, I’d love to know.
Identifying hydrocotyle is a cinch - think buttercup, but in miniature. These are perennial plants that grow from an underground stem, and the leaves are very small (check out how tiny they are compared to the car keys, pictured below) and tend to be kidney/rounded shaped, sometimes with a jagged pattern around the edge of the leaf. They produce tiny pale flowers alongside their leaves, which then produce a moderate amount of seed.
HOW TO CONTROL IT
This can be tricky. There are sprays that are very effective, such as Triclopyr. Most of your garden shop Hydrocotyle products will be Triclopyr.
However, spraying is not usually enough. You need to control the reason why the Hydrocotyle is invading and that’s to do with wet soil. The best control methods involve improving drainage, levelling areas to prevent water pooling, and improving soil structure. These methods can be just as effective as spraying the Hydrocotyle and will give you longer control.