Conserve water by using native plants, good mulch

AS the rainy season gives way to the hotter, drier months of summer, it’s important to consider ways to conserve water in the home garden and landscape.

According to the Environmental Protection Agency, nationwide roughly 9 billion gallons of water per day is used for landscape irrigation. Much of that water is wasted as a result of inefficient irrigation and gardening techniques.

Fresh water is a precious and finite resource here and elsewhere. Population growth coupled with the effects of climate change, such as dwindling rainfall, rising temperatures and reduced stream flow, have diminished freshwater supply. Experts estimate that in some parts of Hawaii groundwater reserves are being withdrawn at or above their sustainable yield.

The good news is that much of the water wasted in landscape irrigation can be easily conserved with simple practices.

WATERING

Much of water wasted in a garden or yard is the result of improper watering. It’s best to water established plants deeply and infrequently. Shallow, frequent watering can lead to shallow root systems and high water loss through evaporation and soil salinization, and can encourage disease.

Regularly monitor soil moisture levels, check plants for signs of water stress and water only when needed. For most plants, deep watering once a week with a slow drip is optimum. Early morning watering, before temperatures rise and winds pick up, greatly reduces evaporation.

To further prevent water loss, water the root zone of plants directly. Studies show that hand-watering is the most efficient, however, properly managed drip and soaker systems can also be highly efficient.

MULCHING

Mulches help conserve water by preventing evaporation, regulating soil temperature, reducing weed growth and minimizing erosion. Depending on the type of mulch, a 3- to 4-inch layer should be appropriate for most applications in Hawaii.

There are many types of mulch and it’s important to look at the advantages and drawbacks of each. Mulches can be organic or inorganic and vary in texture from fine to coarse. A key benefit of using organic mulches is that over time, as they decompose, increase the porosity and water-holding capacity of the soil.

Shredded coconut husks, wood chips, macadamia husks, grass clippings and pine needles are commonly used organic mulches in Hawaii. Lava rock, crushed coral, crushed basalt and volcanic cinder are common inorganic mulches. Rock mulches should be reserved for shady spots and plants adapted to arid climates because they can absorb and radiate heat.

NATIVE PLANTS

Landscaping with natives is another great way to save water. Once established, native plants grown in their appropriate zones can thrive on much less water than many exotic species, often requiring little or no additional irrigation. Also, because they are better adapted to local conditions, native plants typically require less fertilizer and fewer pesticides.

Due to encroachment from development and invasive species, Hawaii is losing its native flora at an alarming rate. Planting natives can help reverse this devastating trend. There are many gorgeous, drought-tolerant native plants to choose from, including ohia lehua (Metrosideros polymorpha), kokio keokeo (Hibiscus waimeae), mao hau hele (Hibiscus brackenridgei), and maiapilo (Capparis sandwichiana).

Kim Perry is a University of Hawaii College of Tropical Agriculture and Human Resources extension agent and the UH Master Gardener coordinator on Kauai. Contact her via email at kperry2@hawaii.edu.