Tropical Gardener Helpline: Over-watering is one of the biggest landscape problems

  • Rain barrels are a great way to save rainwater for future use. (Photo courtesy /
  • Allowing sprinklers to run in the rain wastes water and can leave lots of standing water in your garden. (Photo courtesy /

  • Leaving your irrigation system running in the rain is a colossal waste of water. (Courtesy /

Craig asks: My landscape is all on an irrigation system, but I am thinking I may need to change the settings for summer since we are having more rain. What would you advise?

Tropical Gardener Answer: You definitely want to cut back on your watering times during our summer rainy season. According to a recent speaker in the Community Seed Library series at the Kailua-Kona Library, Micah Barker from Bioscape Hawaii identified over-watering as one of the biggest plant problems in Kona. Too much water can cause diseases like root rot as well as growth spurts that can attract hungry insects. Micah’s general advice was to water deeply and infrequently.


Longer watering times will encourage plant roots to go deeper. This means they will be better established in the soil and can tolerate longer dry periods. Also, it is preferable to water in early morning to avoid leaving wet leaves overnight that are more susceptible to diseases.

Of course, not all plants have the same water needs. Trees and shrubs will have deeper roots than your grass or vegetables and can be watered less frequently. Watering twice a week for larger plants and maybe every other day for grass or veggies should be enough when it is not raining. During rainy season you either have to monitor rain frequency or install rain sensors on your irrigation system. Since it often rains in the afternoon, be sure to turn off your system for the morning following a rainy afternoon. If we have a sunny day, you can leave it on to water according to the schedule.

Rain sensors can save you time and help reduce your water bill. They are available online or at local garden shops, usually for less than $30. They are easy to attach to your irrigation controller and will automatically turn it off when it rains and turn it back on after the storm.

Catching rain water to water, your plants on dry days can also save money on water. Many different rain barrels and rain diversion systems are available online. Check them out if you want to save some of our summer rainwater and put it to good use.

You can actually water less and save some money on your bill by helping the soil retain moisture longer. Mulching around your plants will keep the root zone moist longer and can cut back on your watering frequency. Apply it at least 3 inches deep to be effective but keep it a few inches away from the trunk or base of the plant. You want it in the root zone. With mulch in place you can still maintain a watering time of about 15 minutes, to encourage deep roots, but water less often.

Careful observation or species research can help you determine the water needs of your plants more exactly. Drought tolerant plants definitely need less water and should be on a different station than those that like a consistent water supply. Leafy veggies like lettuce and kale require more water than tomatoes and hard shelled squashes. In rainy season be sure that lettuces don’t get too much water that can cause root rot and other diseases. Many gardeners choose to plant tomatoes and squashes like kabocha toward the end of rainy season in August or September so the young plants can have a good water supply to start but have drier weather once they start fruiting.

All of your plants should be in soil that drains well. If you ever see standing water in your garden, stop watering for a few days until it is gone. To conserve water, consider installing more drought tolerant and native plants that are accustomed to long dry periods.

Hopefully, these suggestions can help your plants stay healthy and thrive in our wet summer season and can save you some money on your water bill.

Email plant questions to for answers by Certified Master Gardeners. Some questions will be chosen for inclusion in this column.

Diana Duff is a plant adviser, educator and consultant living in a dryland forest north of Kailua-Kona.

Gardening Events

Saturday: “Work Day at Amy Greenwell Garden” from 9 a.m. to 12:30 p.m. Meet at the Garden Visitor Center across from the Manago Hotel in Captain Cook. Volunteers will be able to help with garden maintenance and are invited to bring a brown bag lunch. Water and snacks provided. Call Peter at 323-3318 for more information.

Farmer Direct Markets

Wednesday: “Hooulu Farmers Market” 9 a.m. to 2 p.m. at Sheraton Kona Resort &Spa at Keauhou Bay

Saturday: “Keauhou Farmers Market” 8 a.m. to noon at Keauhou Shopping Center

“Kamuela Farmer’s Market” from 7:30 a.m. to 1 p.m. at Pukalani Stables

“Waimea Town Market” from 7:30 a.m. to noon at the Parker School in central Waimea

“Waimea Homestead Farmers Market” from 7 a.m. to noon next to Thelma Parker Gym in front of Thelma Parker Library.

Sunday: “Pure Kona Green Market” 9 a.m. – 2 p.m. at Amy Greenwell Garden in Captain Cook

“Hamakua Harvest” 9 a.m. to 2 p.m. at Hwy 19 and Mamane Street in Honoka’a


Plant Advice Lines Anytime: Tuesdays &Thursdays: 9 a.m. to noon at UH-CES in Kainaliu – 322-4892

Mon., Tues. &Fri: 9 a.m. to noon at UH CES at Komohana in Hilo 981-5199 or

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