Pas­ture weed watch

NZ Lifestyle Block - - Growing - MILTON MUNRO Photo: Harry Rose Wiki­me­dia Com­mons

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.


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.

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