Swales can help trees grow when planting in sandy soils

Gardening on sandy soils is challenging at the best of times and during periods of drought it can feel pointless.  Local gardeners will share one solution at an upcoming workshop on 17 March that’s part of Kāpiti Coast District Council’s Community Garden Parties.

The Paekākāriki community garden group, POG, will host the workshop at their new orchard site behind the sports fields at 162 Tilley Rd (bordering the Holiday Park and Queen Elizabeth Park.) Sites don’t come much more challenging than this – it’s a dry, weed-covered inland dune - but the group will be showing their plans to transform it by creating swales.

Swales are ditches dug along contour lines, across the face of a sandy slope, designed to trap and hold organic matter such as compost and bark chip. This holds more moisture in the soil, making a better environment for plant roots. It’s basically like terracing the slope by using earthworks instead of retaining walls to make stable planting pockets. Plants above the swales help stabilize the soil while the lip below will eventually be used for planting fruit trees whose roots will take in the mulch and moisture held in the swale.

The trick to gardening in these challenging environments, says the Council’s Green Gardener Hannah Zwartz, is to make the most of every drop of moisture, be it from the hose, rain, or dew.

“One problem with gardening on a slope is that the force of gravity means all the water, along with any topsoil or mulch, ends up at the bottom of the hill. Think of the hollows between our inland dunes - that’s where the good soil collects and there’s more moisture. Recreating this landscape halfway up the slope can create rich pockets of soil like there as well.”

Swales are a permacultural technique that can be used on large-scale farms, but also on a smaller scale on any dry bank, Ms Zwartz says.

The workshop, like all the garden parties, will be free. Attendees will learn how to measure contours and create swales and swale creation tailored to their own gardens.

“Bring a spade and strong shoes if you can – and it’s also a chance to find out more about the community orchard plan,” says Ms Zwartz.

The garden parties follow last year’s successful series, celebrating local knowledge on waterwise gardening, food growing, and community building with free workshops, activities, and festivities in seven gardens across Kāpiti, from zucchini sizzles to wheelbarrow races, fruit tree pruning demonstrations to pou whenua-making and wildplay.