Term 4 – Week 1 – Irrigation


Cherry trees in blossom at Bannockburn Road

Term 4 has begun! A lot of changes happened over the last two weeks while it was school holidays. There is tons of blossom everywhere, on the vines buds have burst and leaves are starting to grow and the plants in the nursery have really shot up.


Tomato plants in the glasshouse


Baby cherries

Weather this week has regressed back to winter! It even snowed in Queenstown. There was a lot of rain overnight on Tuesday, about 32mm. One of the lecturers commented that it was the most rain in one go for about 4 or 5 years. Perfect timing since this week was all about irrigation!

Having a good irrigation system will help to get the maximum yield from a crop. Here in Central Otago there are two sides to irrigation. Irrigation of plants and frost fighting. Both need a huge amount of water, particularly frost fighting.

1mm of water over a hectare equals 10,000 litres of water. Here in Alexandra the annual rainfall is only about 400mm, some years as low as 280mm and growers will need to top that up with about 1000mm of water (not including water for frost fighting).

On Tuesday we went to McArthur Ridge vineyard to look at their irrigation system. It is a large property of 140 hectares so they have a huge irrigation system. They have two dams onsite where they get their water one for irrigation (15m deep!) and one for frost fighting. It was amazing to see the scale of the operation.


Half of one of the dams at McArthur Ridge – too big to get in one shot!



Pumps and filters for irrigation at McArthur Ridge vineyard


Two of the thirteen motors that run the frost fighting. $1.5 million worth of motors!

Orchards and vineyards will need to start irrigation from about now until the end of the growing season. To figure out when to irrigate you either need to run a water budget using evapotranspiration figures (Et) or have moisture sensors in the ground.

Evapotranspiration measures the combined loss of water from plants and soil. So the amount you would irrigate would be Et minus any rainfall. In summer Et can be 6 – 7 mm a day.


This week in propagation we did softwood cuttings of thyme and lavender. Softwood cuttings are taken in spring, using the new growth. Good plants to propagate using softwood cuttings are lavenders, hebes, lilacs and magnolias.

The cutting should be about the length of your little finger, taking the cutting just below a node. Keep the cuttings cool, mist and definitely keep out of the sun. The sooner you can get them done the better as they will wilt quickly. Remove any flower buds as they will keep trying to grow the flower instead of new roots. Dip the base into Seradix 1 hormone. Plant into a mix of half potting mix, half pumice. They should root in about 2 – 5 weeks.


Olivia, Mandeep and Pranel concentrating on the fiddly cuttings

Lavender is a great plant for Central Otago since it doesn’t need much water and can handle the sun. They have a faint fuzz that holds onto water, stopping evaporation. They are pretty low maintenance only needing to be pruned once a year after flowering. There are so many different varieties and even colours. I like the kind that looks like it has little petals on the top (they are technically leaves) but they don’t handle frosts very well.

lavande papillon lavandula stoechas 08d cpf 781

Lavandula stoechas (French lavender)

Last week’s weather:


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