Next summer I will try to deliver water more efficiently to the plants that need it, using rain water and household grey water as much as possible. This year we have had a taste of what gardeners in many other parts of the world struggle with all the time; perhaps we can learn from them.
Raised vegetable gardens are great because they drain well and allow the soil to warm up quickly in the spring – but they drain too well in a drought. Instead of the ubiquitous use of hoses, many vegetable gardeners create furrows between their rows of vegetables. Plants are watered by flooding the furrows. Deep root systems develop, and it is easy to empty watering cans into the furrows, or fill them with a soaker hose. Several days can go by without watering.
Seedlings are planted into a shallow groove along the ridge top and watered separately until they are large enough to benefit from the flooding. Often gardeners drape black landscape fabric over the ridges. Not only does this prevent erosion, but soil is not splashed on to tomato leaves, and strawberries keep clean.
In a garden, furrows are blocked at either end, acting like long thin puddles. In well-drained, sandy soil, the furrows have to be closer together than in a soil that holds water better, so add organic matter to the soil at the beginning of the season to improve its water holding capacity. The depth of the furrow depends on the expected root ball of the crop.
This advice comes from Arizona: Furrows deliver water alongside the plant row. Water is kept in the furrow long enough for moisture to infiltrate the soil of the root zone (http://extension.arizona.edu/pubs/az1435.pdf).
From Texas: Furrow or flood irrigation is the oldest, cheapest and most low-tech form of irrigation. Stored water or rain surges into the furrows, the water slowly infiltrates the ground, and less water is lost through evaporation. In 2000 over half the fields in the US were irrigated in this manner (https://jbgorganic.com/blog/2009/03/let-it-rain/).
From Spain: When they do get rain here, it is often a heavy deluge that collects in the furrows (http://fincafood.com/2012/04/16/spring-planting-part-1-water/).
In a perennial garden, or around shrubs, use the same method. Create a decorative pattern of ditches, or winding furrows, snaking through the bed, around compact groups of plants or individual shrubs. Fill these dry streambeds with attractive rocks, and cover the planting spaces with your favourite mulch. The plants flourish (or at least survive) because there is water for their deep roots whenever it rains or the ditches are filled with grey water.
At the end of the season, when the ground is saturated again, unblock the ends of the furrows and dry streambeds, and they will become drainage channels. Or simply rake the soil smooth and sow some fall rye or other green manure to prepare the garden for next year’s crop.
— Sheila Watkins, Master Gardener