Our District

Low-tech, low-cost, low-pressure irrigation

By Hannah Zwartz, Green Gardener

Isn’t it too early to think about irrigation? This year we’re trialling several underground systems in community gardens. These need to be installed at planting time so as not to damage roots later – even though they may not be needed until January. It’s all about getting water deep into the soil, making deep-rooted plants that won’t wilt when things get hot.

Efficient irrigation keeps water bills down, but there are other advantages too. The less water we waste in gardens, the more can stay in our rivers and streams. For me, convenience is also a big motivator - well set-up watering systems means more time at the beach, because you aren’t tied to the end of a hose all summer. Plants can thrive even if you want to go on holiday; a weekly check of reservoir tanks is all that’s needed.

Here are three low-tech, low-cost irrigation options: We are focusing on systems that work well on low pressure eg. from a rain tank barrel. These ideas come from David Bainbridge’s fantastic handbook `Gardening With Less Water’.

 

Deep pipe: Ideal for trees – this is how MOA community orchard in Jeep Rd Domain, Raumati South, established fruit trees on windblown, kikuyu-clad sand dunes. Five years on the trees are now starting to fruit. A length of plastic pipe was buried upright next to each tree so water poured into the top gets down to the subsoil to encourage deep roots. Bainbridge recommends 40-60cm lengths of 5cm-diameter pipe for hand-watering (thinner pipe could be used for drip irrigation systems.) He drills holes 5cm apart down the length of the pipe and covers the top with a zip-tied piece of screen or shade cloth. MOA filled their pipes with pebbles instead. Large hollow bamboo could also be used.

Left: Deep pipe in the foreground at MOA (Kath Irvine doing the first winter prune).

Porous clay pots: I’ve been using this for my tomatoes for a couple of years now with great results. 10 times more efficient than surface irrigation because the amount of water used is largely determined by how much water the plant is using. “It’s almost like an iv line for a person,” says Bainbridge. An added bonus is that weeds are reduced, as are pests and diseases- the plants don’t get stressed, and water is kept well away from leaves and stems.

1. Collect terracotta pots (as large as possible- the smaller they are, the more you will need). They must be unglazed.

    21cm terracotta pot for $3.98 at Bunnings

    25cm terracotta pot for $7.50 at Mitre10

2. Bung up the bottom holes using a cork or sealer/glue

3. Loosen soil across the bed, and bury pots where needed. Keep the rim poking above the soil, fill with water then put a lid on.

4. Leave overnight to see how far out the water seeps- plant your seedlings in this zone (usually within 10cm of pot). A 25cm pot might water 3 tomato plants – but leave room so you can reach the pots for watering once the plants grow.

Left: A terracotta pot and well-mulched tomato.

Refill pots as needed- at first, they should last a week but as things dry out they may need filling every few days. Next month we will look at how to set up a system to keep the pots full automatically. Terracotta pots will be seen in action over the summer at Matai Community Garden, Raumati, or at Kāpiti Community Centre, Paraparaumu (workshop Monday November 7, 10am-12pm.) Porous clay pots were used this way in China 2,000 years ago, and have also been traditionally used in drylands across Latin America (where they are called ollas), and from the Middle East through to India.

Wicks: A wick is made from 1cm-diameter nylon rope, washed to remove any oil. One end goes into a reservoir (anything from a 2l plastic bottle, to water containers, to a 20l pail or 200l barrel out in the garden). The other end goes to the plant roots, either beside an individual plant or buried under a row of beans/lettuce etc. Vinyl tubing can be used to create either a capillary-form wick (for real slow release- the plant only sucks out what it needs) or a gravity-fed form, where the reservoir is above the wick (water drains more quickly, but still much slower than a traditional seep-hose. See the book or website for more details).

You will be able to see wicks in action this summer at Paekākāriki School garden.

 

The Council Green Gardener, Hannah Zwartz, offers sustainable and waterwise gardening advice to local residents, community groups and schools.

Community Visits and workshops are free. 

To contact the Greener Gardener, call the Council on 296 4700 or 0800 486 486 or see www.kapiticoast.govt.nz/greenservices

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