On a grassy ledge carved into their steep Kuliouou hillside, Kevin and Susan Mulkern stood in the shade of a spreading kiawe tree. A swing hung from an outstretched limb, which was reinforced by a crutch planted in the ground.

The Mulkerns, landscape contractors, could have removed the kiawe, an invasive species, after they bought the property in 1979. They’re grateful that they let it be.

“This tree saved our child’s life,” Kevin Mulkern said, pointing out a crack that split the branch where it met the trunk. “About 15 years ago, a big boulder fell from the cliff. It fractured this branch, sheared off several other major limbs and kept going, but the tree had broken its fall.”

At the bottom of the hill stands the wood-frame house, where, on that rainy, windy afternoon, the Mulkerns’ daughter, Dorothy, then 14, was home alone in her room at the back.

“It was New Year’s Eve. Dorothy called me at work and said a rock had crashed into her room,” Mulkern said. “I thought she was joking and hung up on her. Then we rushed straight home.”

“The boulder gave Dorothy a ‘garden view’ and scared the lights out of her,” Susan Mulkern added.

Through the gaping hole, the Mulkerns saw more damage: The 5-foot-tall rock had felled a paperbark tree before taking off the corner of the house and rolling down the side path to the front door.

As a result, trees hold a special place in the Mulkerns’ hearts and the garden on their 11,334-square-foot lot, much of it nearly vertical. “We’re planting trees instead of adding rockfall mitigation fences,” Kevin Mulkern said, explaining that other rocks had come down along with the boulder and rockfalls are common in the area.

THEIR house on a raised foundation, has picture windows on all three sides of the living room. Instead of curtains, the surrounding trees have been pruned so that the interlacing branches give privacy and shade. It started when an arborist friend advised that dead wood be trimmed from the pink tecoma trees planted along the street by the city, and continued when the Mulkerns saw the possibilities.

“It’s beautiful,” said Susan Mulkern, who used to work for her father, designer Alfred Shaheen. “We’re looking at greenery, flowers, birds … and trees are great noise and air filters.”

Melaleuca trees, also known as paperbark, screen the side bedroom into which Dorothy moved after the boulder fell. Out back, Rhapis palm and more paperbark trees guard the house.

“In 1979 it was all dry grass, haole koa and barbed wire; this was a ranch in the old days,” Kevin Mulkern said as he led the way up the hill on switchback trails set with steps made from old railroad ties. Terraces were held in place by dry-stacked rock walls — some made with rocks from the New Year’s Eve fall. Pausing to admire their lychee and lemon trees, pomegranate bush and wild basil, they reflected on their progress over 35 years.

“Other people’s gardens always came first.”

There was purple-flowering vitex — a jungle of it — when they first arrived. They cut it back and shaped some of it into topiary balls.

Orange-flowering cape honeysuckle, bright “red dragon” orchids (Renanthera kalsom) and bromeliads added splashes of warmth. “Because Dorothy liked the rock face, we made little puka and planted red bromeliads there.” Coppery vriesea grew waist-high, the mother plants sending out babies on stalks.

Terraced lawns were green with emerald zoysia and Korean temple grass; another ground cover, wedelia trilobata with yellow flowers, “used to be common along Waialae and Red Hill by the freeways,” Kevin Mulkern said. And there are rescue plants: a cactus washed by waves from a Portlock yard, a Surinam cherry that a client no longer wanted.

With its rugged volcanic ridgeline etched against the clouds, Kuliouou feels like a prehistoric valley, a land that time forgot. The Mulkerns moved here from Sunset Point to be nearer to their East Oahu business.

“I worried because after driving home from work, Kevin would be paddling out in big Sunset surf as night fell,” said Susan Mulkern, who first met her husband as a teenager on Kuhio Beach as he came in from surfing.

“The open space on the hill reminded us of living by the ocean,” she said.

After a day of alternating rain and sun, a mist moved onto the hillside, smelling of the sea.

At the top of the garden, on the big grassy terrace they built around the kiawe tree, the Mulkerns admired an overhanging curtain wall of lava rock held in place by a cage of white banyan roots. It’s nice up here at night, too, they said, especially with Champagne and fireworks over Maunalua Bay. Then, holding hands, they slowly descended the hill.

“Garden Party” spotlights unique and exceptional gardens. Contact us via email at features@staradvertiser.com or call 529-4808.