SFPUC Growing Plants in Hospital-Like Nursery to Protect Water Quality

Most plant nurseries are a scene of colorful chaos — bags of soil strewn about, pools of water collecting beneath ceramic pots, and a patchwork of plants existing in tight quarters. But these conditions can create a breeding ground for plant diseases.

So, the San Francisco Public Utilities Commission is trying something different at its new native plant nursery in Sunol. To avoid infecting plants, the botanists here take precautions more akin to a laboratory than a commercial nursery.

The nursery sits atop the Alameda Creek Watershed, which lies east of Fremont. Here, dry grasses paint the surrounding Diablo hills golden, with dense patches of dark green oak trees.

The SFPUC owns 35,000 acres of land in the watershed, which supplies up to 30 million gallons of water a day to Bay Area residents.

But beneath the surface of the grass, funguses that have spread through the soil attack plant roots, causing decay and ultimately death. Up to half of the tan oaks and 1 in 5 coast live oaks in this area died over a 10-year period due to sudden oak death, according to the SFPUC.

Native California flora such as oaks, mugwort and monkeyflower are vital in watershed habitats to filter pollutants and prevent erosion. But theses species have often succumbed to quickly spreading disease. When the commission had to plant these natives in the Alameda Creek Watershed, it took extreme measures to prevent infection, but they were ineffective. So now, the commission is growing its own native plants. If successful, the project could provide a new model for restoring disease-ravaged ecosystems.

The commission will finish planting the first batch of Sunol nursery- grown natives, like rushes and iris-grasses, by the end of June.

Stringent Measures Were Ineffective

Under state and federal law, when the commission wants to build anything on watershed land, subtracting habitat, it has to compensate by planting additional native plants, says Tim Ramirez who manages the SFPUC’s natural resources and lands division. When the commission undertook such a project in the Alameda Creek Watershed, it knew native plants coming from commercial nurseries might spread botanical diseases in the landscape.

So it required nurseries growing the plants to place the natives over 3 feet off the ground and for nursery employees to disinfect their shoes. It also asked contractors working in the field to wear clean clothes, and clean their boots and equipment before work. The PUC also tested natives for pathogens before and after they were planted in the watershed. But still, nursery-raised trees such as oaks and sycamores and shrubs like mugwort and monkeyflower brought disease into the landscape.

“It’s counter-intuitive to the goal of restoration, if you’re planting plants that are already sick,” says Mia Ingolia, a biologist and botanist with SFPUC.

The commission decided to try growing its own plants.

Nursery Like a Hospital

To keep plants disease-free, the Sunol Nursery uses sterile techniques more often seen in labs. Any seeds entering the nursery must be bathed in bleach, and botanists use latex gloves and spray  stainless steel planting tools  with disinfectants.

On entering and exiting the nursery, all visitors must bathe their shoes in soapy water. No trucks or contractors can enter the grounds. Trucks dump soil from outside, over a gate and into a loading station. From there, the team takes buckets of soil to a “steamwagon,” where dirt is steam-cleaned to get rid of weed seeds and plant diseases.

Before the native plants are put in the soil, they’re certified to be root-rot free. To do this nursery workers water the plants and catch the water. They then take an organic green pear, prick it with a needle, and place it in the captured water.

“After three days, if you look at that pear, and it has a lesion on it, that looks like a rotting pear that you see on your counter … and it’s not mushy, it’s hard, then you know that you have a positive,” Ingolia said.

So far no plants grown in the Sunol nursery have tested positive.

Seed to Soil

SFPUC contractors will finish planting the first batch of plants in June. These plants are being used to create areas in an on-site industrial yard where runoff and rainfall can collect and be filtered through the native plants before entering the watershed. This will help improve the clarity of water moving from the yard into the watershed.

But “it may be a while until native species like oaks are able to be planted in the watershed,” said Ramirez.

While state and federal regulators like to see oaks that are already mature being planted, the commission is taking a different route. In the future, it wants to plant certified disease-free acorns in the ground.

“They want you to mitigate right away and plant and have it be restored as quickly as possible,” says Ramirez, “so we have to ask them also to be patient.”

But, he says, the extra time it takes to grow your own native plants is worth it in the fight against plant diseases.

“Because once you have [diseases] in your watershed, or you bring them into your watershed, it’s even more expensive and time- consuming to try to minimize the risk, or if you are brave, to try to eradicate some of these things.”

This summer, the team will head back out to the watershed to collect more native plant seeds. This time they’ll collect flowers like California poppies, fiddlenecks and lupines, and start the next round of plantings in 2020.