Photo by Alan Decker

Kate Sessions Balboa Park Nursery. You could live in San Diego all your life and never notice the inconspicuous sign that marks the nursery's entrance just down the hill from the Frisbee golf course on Pershing Drive.

On the morning after one of those record-breaking cold nights this past January, Mike Rasmusson checked on his charges. Rasmusson supervises the Kate O. Sessions Balboa Park Nursery -- the city facility where many of the park's plants get their start in life. Behind the nursery's hothouses and administrative offices, he stopped at an outdoor table and peered down at a group of four-inch plastic containers. "Ohhhhh, shoot!" he moaned. "This is Ficus macrophylla, the Moreton Bay fig. These are the babies."

The carnivorous specimens can't tolerate the salts and other minerals in San Diego's tap water.

Photo by Alan Decker

The fig-tree sprouts, grown from tiny, almost invisible seeds that had been buried in the pots for more than five months, had shriveled and turned black overnight. Had they withstood the frost and thrived for a hundred years, each might have rivaled the magnificent giant that reigns over the lawn next to the Natural History Museum. But now they were dead. Rasmusson shrugged. "You just have to take it in stride and say, 'You know, let's try it again.'"

Balboa Park eucalyptus. During most of the 20th Century, the eucalyptuses seemed to be pest-free. Then in the 1980s, an Australian beetle began chewing its way through eucalyptus species in Southern California.

Photo by Alan Decker

It helps to be dauntless when it's your job to maintain the park's status as a horticultural showplace. Apart from the 150 acres of coastal sage scrub preserved in Florida Canyon, the landscape of Balboa Park's 1172 acres is a wholly unnatural creation, filled with species imported from every continent except Antarctica. The plants have to be watered and mulched and pruned and fertilized and protected from deleterious weeds and bugs. As they die or grow tiresome, they have to be replaced with others both eye-pleasing and apt to thrive.

Mike Rasmusson in 2000 became the first city arborist — looking after all the trees in all of the city's 340 parks.

Photo by Alan Decker

Who decides what goes where? "Right now, I'm pretty strongly involved with that," Paul Sirois said, "but we draw on a lot of folks."Sirois is one of two district managers in charge of the park. He holds a two-year degree in park management and design and a bachelor's in environmental horticulture, but when he joined the city parks staff in 1993, he started "from the ground up." As a maintenance worker, "I did everything from cleaning restrooms to edging turf," he says. He later advanced through the park department's supervisory ranks and in 2000 became the first city arborist — looking after all the trees in all of the city's 340 parks. In December 2005 he was promoted to the position of horticulturist for Balboa Park, and when the district manager's position opened up last year, Sirois applied for it. "I love the park, so I thought I'd give it a go."

Paula Root likes to tuck orchids throughout the Botanical Building.

Photo by Alan Decker

He now oversees about 60 people, including 45 grounds maintenance workers, 5 rangers, 4 gardeners, 5 supervisors, and a horticulturist. Augmenting his team's labors are citywide crews that handle certain tasks, such as mowing the expanses of lawn adjoining Sixth Avenue and at Morley Field. The central crews cut those weekly using seven-gang mowers and smaller trim machines, but Sirois's crews go behind to weed-whip and edge and blow the clippings. "We also do some hand-mowing in areas that are too small, such as the strips of lawn near the Organ Pavilion."

Desert Garden, Balboa Park. Sirois wanted the new Zoo Place plantings to "kind of match" the Desert Garden across Park Boulevard.

Photo by Alan Decker

A separate citywide crew attends to routine pest management for San Diego's parks. "We're trying to get away from chemical use as much as possible," Sirois says. Mulch and mechanical weeding are used to discourage herbivorous invaders, but when herbicides and pesticides are unavoidable, the centralized teams apply them. Balboa Park's gardeners and grounds maintenance workers are on the front line in diagnosing problems. "It's really a combined effort of everybody being aware and watching what's going on." The volunteers who toil in the rose garden are constantly monitoring the roses to see when they've got too much rust and need to be sprayed, Sirois says. Because of his years of working as the city arborist, Sirois himself has been involved with diagnosing tree maladies.

No tree in the park has been more beleaguered in recent years than the eucalyptus. First brought to California during the gold rush, eucalyptuses were later thought to be a good source of wood for railroad ties, but people soon learned that the young trees grown in California lacked the strength of the several-hundred-year-old specimens that Australians had harvested from their virgin forests. Still, early Californians liked how fast eucalyptus matured, Sirois says. "And they were pretty drought resistant." He thinks that's why so many were planted for the 1915 Panama-California Exposition, the event that kicked off the transformation of the park from an almost treeless wasteland to a garden paradise. "They grew so fast, and you had a pretty good shade canopy pretty quickly."

During most of the 20th Century, the eucalyptuses seemed to be pest-free. Then in the 1980s, an Australian beetle known as the eucalyptus longhorn borer began chewing its way through eucalyptus species in Southern California, killing many of them. Since then an almost biblical series of plagues has descended upon the trees: "at least 16 different pests in the past 17 or 18 years," Sirois says. Dying eucalyptuses have become a common sight, not just in the park but throughout the city.

Most of the time, scientists have found ways to vanquish the pathogens. That was the case with the red gum lerp psyllid, a tiny insect that in 1998 began showing up on the leaves of the red gum eucalyptus and a few other species. The psyllids sucked the sap from leaves, an insult that caused defoliation. As the denuded trees weakened, Sirois and other local arborists feared that up to 1000 might be lost. But a Berkeley entomologist went to Australia and found a tiny stingless wasp that was a natural predator of the lerp psyllids. He imported the wasp to California. "For a while, they had to delay the release because a different type of psyllid was being used in Florida to control the overgrowth of melaleuca trees there." There was some concern that the wasp might attack the Florida psyllids, but it turned out not to be a problem, Sirois says. Once introduced here, the wasps spread, and the red gum lerp psyllid population came to be "very well under control." Sirois says another psyllid began attacking lemon-scented gum eucalyptus around the same time, but it turned out not to be a tree killer, as had been feared.

Another problem has proven more intractable. "We first noticed it in 1999," Sirois explains. "We'd see something like a brown stain that would go up the side of the trunk of the tree. It mostly seemed to start at the bottom, although we've found some trees where it looks like the top branches are being affected first." In the areas of the stain, the bark dries and cracks, and one by one, branches lose their leaves and die. From a distance, it can look as though the tree is rusting to death.

In a grove, "You may see one tree get it, and then a little while later another tree in the grove will get it, and a little while later another tree will get it," Sirois says. "But in general, we haven't seen whole groves disappear." As a preventive measure, park personnel have sprayed the bark of some trees with an antifungal chemical. "It's certainly not hurting, and a lot of the trees we've treated have not come up with any kind of disease," Sirois says. "But it's too early to say whether it's helping." Also, the fungal spray doesn't work once the tree is diseased; no infected tree has ever recovered.

Most frustrating has been the inability to figure out what's causing the malady. "Several possibilities have been thrown around," Sirois says. "But nothing has really matched up to what we have." He says authorities have conclusively ruled out the funguslike organism that causes sudden oak death. "There's also a disease called Mundulla yellows that they have down in New Zealand and Australia. It's pH-related, and we thought maybe that would have something to do with it." But the pH of the soil around affected trees hasn't "really fit the bill," Sirois says. "We thought of Xylella — the bacteria that's currently affecting the wine crop and oleander. But that was tested and ruled out." This past winter, the advance of the mystery ailment seemed to slow, a possible consequence of the cold weather, Sirois speculates. "But last summer and spring were pretty bad. We lost quite a few large trees. I would say 30 to 50."

The primary victim has been the sugar gum (Eucalyptus cladocalyx), although a number of honey-scented gums (Eucalyptus melliodora) and silver dollar gums (Eucalyptus polyanthemos) have also come under attack. The towering sugar gums also happen to be the most prevalent tree in Balboa Park, a fact that was documented when the first-ever Balboa Park Tree Survey was conducted in 1998. "It was an old-style survey, prior to GPS," Sirois elaborates. Brass pins were driven into the ground every 250 feet; then teams counted every tree with a diameter of two inches or more within each grid block. The final tallies revealed 15,271 trees (including 348 separate species). Almost 5000 of the total were some variety of eucalyptus.

That large percentage worried Sirois and the park horticulturist at the time, Kathy Puplava. "If you grow a monoculture, you're susceptible to losing the whole tree population," Sirois explains. "Back East, Dutch elm disease wiped out all the elm trees." So in the wake of the survey, the two developed a park reforestation plan that emphasized the goal of making Balboa Park's tree population more diverse. Sirois says probably 30 species have been added to the park in the years since then. But he adds that it hasn't been easy to find substitutes for the really big eucalyptuses.

Trees that are skyscrapers in some areas often don't reach the same heights in San Diego's dry climate. The coast redwoods planted in Balboa Park's Redwood Circle during the 1920s stand only about 80 feet tall, compared to the 300-plus feet they attain in Northern California, where summer fogs bring moisture to the uppermost branches and free the trees from the need to transport water up that high from their roots. Sirois says another limiting factor is the park's soil, much of it hardpan and impenetrable below a depth of just a few feet. "We don't have the deep alluvial soils that they have in Pasadena," he says. "You see huge, magnificent trees there."

Some species do grow as tall in San Diego as the eucalyptus. The star pine (Araucaria heterophylla) and bunya-bunya (Araucaria bidwillii) do, Sirois says, but their silhouettes look nothing like the broccoli-esque forms of the sugar gums and lemon gums. (Bunya-bunyas have outstretched, almost prehistoric-looking branches, while star pines grow into the classical shape of Christmas trees.) Torrey pines can reach great size. "But as far as function — meaning having that willowy top but very tall — there really aren't any trees that match the eucalyptus, and that's something we've struggled with."

Sirois has talked with the urban forester from the City of Los Angeles about what L.A. is doing to replace tall-canopy trees. "One they're trying is the pecan tree. So we've planted a few of those in the park." The turpentine tree (Syncarpia glomulifera) "gets pretty tall," Sirois says. "It's close to the eucalyptus family." Familiar eucalyptuses will also continue to be planted, he adds. "We've planted sugar gums in the last six years. But we're just a little more selective in where we plant them. We're not putting them right next to buildings anymore." The risk of branches dropping off or trees falling is too great.

Sirois says the park's reforestation plan recognizes the importance of diversifying not just the types of trees but also their ages. When the 1915 and 1935 expositions were being readied, "Thousands and thousands of trees were planted all at once," he reminded me. Most weren't that old, perhaps four to five years, so they're maturing around the same time. Sirois thinks the fundamental explanation for the recent eucalyptus woes could just be that the trees are reaching the end of their natural lifespans here and in their waning years are susceptible to disease.

To ensure that future generations of Balboa Park managers don't face the same problem, "You really want to continue planting all the time," Sirois says. "That's critical to maintaining a healthy urban forest with old trees, middle-aged trees, and new trees." In practice, "We generally try to plant around 200 trees a year." When a stormy year destroys more than 300 trees, as happened in the winter of 2003-2004, "we'll try to accelerate the replanting then. But as a standard, we try to keep it around 200."

In deciding where to plant new trees, Sirois says he and his staff are guided by the master plan developed for the park in the late 1980s. "We may change plant material, but we don't try to change the function of the various areas." They wouldn't, for example, plant a new grove in the middle of one of the big expanses of turf on the west side of the park. "They're passive park areas, so people can have picnics and other gatherings. We try to respect those layouts."

Earlier master plans also influence current thinking. Samuel Parsons Jr., the Central Park superintendent brought to San Diego from New York City in 1904 to develop the first plan for what was then called City Park, "was very big on the views at the edges of the canyons," Sirois says. "He wanted to have trees every couple hundred feet or so to provide a frame but not to eliminate the view." Although buildings in the park and downtown have obscured many of the sweeping vistas, some remain, and "we try to stay respectful of all that," Sirois says. "We want to make sure we still maintain some of the view corridors."

Within those broad guidelines, lots of factors direct where a new tree is planted. Input from local residents sometimes influences what gets planted where. One example is the Trees for Health Garden, located on the northeast corner of Quince Street and Balboa Drive. The original inspiration for it came from San Diego Herb Club members, who about ten years ago got a small grant to promote awareness of medicinal trees in Balboa Park. Major plantings on the site were started in 1998, and today everything from the African sausage tree to the white popinac lines the gravel paths. The park's gardeners have continued adding trees and shrubs to expand the scope of the garden.

It's not unusual for citizens to ask that a tree be planted to commemorate the passing of a loved one. Several hundred trees have been planted in honor of someone over the years, according to park staffers. Sirois says they normally will tell the bereaved party which locations and trees are available. The charge for arranging such a ceremony is $200. "We'll usually plant the tree three-quarters of the way and leave a little pile of soil so the folks can come and do their memorial service," the manager says. Plaques used to be installed, but no longer. "It just got to be too many," Sirois explains. "It became a maintenance problem, and it also kind of was taking on the appearance of a graveyard."

When it comes to flowers and shrubs, Sirois says that 15 areas of the park have been designated as specialty gardens, and "the specialty gardens are themed out." In those areas, "We're pretty much trying to match the theme of what's already there. In the Desert Garden, we're bringing in desert plants. In the Rose Garden, it's roses." Sirois adds that the park staff also tries "to bring in new plant material that's being introduced in the industry. Something we're planning on using in the future are some of the new bougainvilleas that are being developed right now. There are also new podocarpus varieties that have just been introduced. We're going to start incorporating them with some of our plantings. So we're trying to keep on top of the industry, but at the same time, we do have to match form and function to what's already in the landscape."

No place in the park sees more continual change than the Botanical Building. Dominating the area just north of the reflecting ponds, it was touted as the largest lath structure in the world when the 1915 exposition opened. None of the original plant specimens survive. The Navy turned the place into a warehouse during World War II, and several renovations also disrupted the building's function as a conservatory at various times during the last century. Mike Rasmusson says only a few of the largest specimens that were growing in the building before 1994, for instance, were preserved during the makeover that took place that year. One was the wide clump of Formosa palms at the eastern end of the building. "I love that palm," the nursery supervisor enthused on a recent chilly morning. "The blooms smell kind of like oranges and pineapples. You can even smell them outside!"

I was meeting with Rasmusson and Paula Root, the nursery gardener who works full-time in the Botanical Building. Rasmusson held Root's job back in the early 1990s, so he had the task of redesigning the beds after the 1994 renovation. It's rare to meet people who take such evident pleasure in their jobs as these two. "I'm probably the only lady on my street who can't wait to get to work," Root confided. "My husband's always asking me, 'Why are you leaving so early?' "

"I used to do the same thing!" Rasmusson exclaimed, recalling his days as the Botanical Building's chief gardener. "I used to come in early and have my coffee and just walk around and go, 'Hmmmm. What am I doing today? I'll do this project!' You see jobs that you need to do, and it's really fun."

It was a Thursday, the one day of the week the building is closed, and Root had started her morning by working on the big circular display in the center of the building. The day before, it had been filled with a sea of vermilion poinsettias, but she had moved all those pots to a back room where they would be given away to the public, first come, first served. What remained within the circle was the gigantic fishtail palm (Caryota obtusa) that Rasmusson planted when it was only about 12 feet tall. Now it looks as though it's ready to punch through the lath roof. Rasmusson says it will be replaced sometime this year, before it does any damage. "We were talking about using another type of palm in there, but we decided to plant another obtusa. We want that spectacular show."

Dark-green-bladed lilyturf and chartreuse Myer's asparagus are the only other permanent plants within the central circle. "When we developed this place, I needed something that would just kind of sprawl out and hide containers," Rasmusson explained. "They do their job." Within the bright green circle of the asparagus plant's fluffy plumes, Root tucked dozens of pots of epidendrums, some bearing clusters of purple blooms on their tall, reedy stems, others laden with orange and red flowers. On the level below them, she planned to place frilly purple-and-white Willis Harrington orchids. The orchids had been sent over that morning from the park nursery. They would remain on display, Root told me, as long as they continued to look good. "The challenge of being a gardener in this building is the rain," she said. If raindrops penetrated the building's wooden slats, the Willis Harringtons would develop unsightly brown spots. "I'm crazy," she confessed. "I've been known to move all the orchids inside because a big storm was coming."

"If it hails, it's all over," Rasmusson added.

After the Willis Harringtons stopped being presentable, Root would replace them with cymbidiums grown in the nursery. "Then in May you have your epiphyllums — your orchid cactus," Rasmusson said. "We're always out there, looking for different plant materials to put in here."

Root likes to tuck orchids throughout the Botanical Building so that visitors are constantly confronted with their striking colors and forms. If the orchids are the most obvious plants that change weekly, they're not the only ones. Root drew my attention to the raised bed filled with pots of lavender, echinacea, borage, menthol, aloe vera, sage, and other plants used for medicinal purposes. Most of them were sun-lovers, Root explained. The relatively shady conditions in the Botanical Building wouldn't permit most ever to bloom. But "Susan Masing grows these outdoors," Root said. Every Thursday, Masing, another of the nursery gardeners, brings good-looking specimens over from the nursery and removes any that look bedraggled. Masing also changes the plants on the "touch and smell" bed that Rasmusson created years ago. "We had people coming in here touching the orchids and bruising plants," he recalled. To channel that urge, he assembled scented geraniums and other fragrant-foliage specimens. "Everybody loves it," Root attested. "But it gets pretty much torn up every week. Because the kids and adults get excited, and instead of just touching it, they pick things."

It's fun to wander through the building with Rasmusson. Most of the plants that today look huge and dramatic were but a fraction of their current size when he selected them a dozen years ago, and his obvious pleasure in their transformation is contagious. When he planted the monstera vine near the front entrance, for example, he was hoping it would someday insinuate itself around the main door, greeting visitors with its big beautiful leaves, and it's done just that, "Like you see right now! You get that automatic tropical feeling!" The flame-thrower palms were barely taller than Rasmusson when he installed them along the building's eastern wall, but "now they're at least 15 feet tall!" he marvels. "I put them in because when their new foliage comes out, they have a nice maroon color, and they have the really nice fronds. But when you're standing in the back of the building, I also wanted that big grand look."

Rasmusson reused a lot of the bedding plants that had been in the building before the '94 renovation, but he organized them differently. "Everything had been pretty much everywhere. There was really no semblance of order, and I wanted to have it be more tour-friendly." So he developed themes, such as the bed devoted to plants of economic importance (bananas, allspice, coffee, and more). There's a woodland area and a dracaena area and a bed filled exclusively with bromeliads. "Before you couldn't get a sense of how many varieties there are," Rasmusson says. Now the profusion of different leaves and petals makes it obvious.

For a while, the beds bore plaques identifying their themes, but these were stolen over time. The park staff recently has had a new motivation for replacing and expanding signage: they're in the process of applying for the Botanical Building to be designated an accredited botanical garden by the American Association of Museums. But even without the formal designation, Rasmusson says he's always thought of the conservatory as being museumlike -- a place designed to teach visitors about its contents. He's astounded whenever he runs into a San Diego resident who's never been inside the building. "Paula does the most awesome job! Even better than when I was here! I'm jealous," he teased.

Root batted away the praise. There's so much to do, all of it engaging, she indicated. Many plants must be hand-watered; she can spend up to an hour a day at that in summer. When it's dry, she mists the tillandsias every day or so. She hand-sweeps the aisles and prunes almost everything. Certain beds require special ministrations. The carnivorous specimens can't tolerate the salts and other minerals in San Diego's tap water, so once a week Root uses a hand pump to remove the water in their swampy bed, and she replaces it with new water that she has filtered. She uses pesticides only as a last resort, instead washing down plants at regular intervals to discourage infestations. "People crack me up," she says. "They'll ask me, 'Where are the bugs?' I say, 'Trust me. I know where they are!' "

In addition to all the routine chores, "There's constant change, because things get old," Root told me.

"Yeah, I remember you came to me when this was a brunfelsia bed," Rasmusson said, standing at a spot near the building's southeast corner. He explained that the brunfelsia, commonly known as Yesterday-Today-and-Tomorrow because of the way its flowers change color, wasn't blooming well; the light wasn't bright enough. Root suggested tearing it out and instead planting a tiny grove of miniature fishtail palms. "They were over at the nursery, and I thought it would look really cool to plant a bunch of them together," Root recalled. Rasmusson encouraged her, and the result, tucked between a cluster of bamboolike palms and a statuesque tree fern, is a striking detail within the verdant tapestry, if one that many visitors never notice.

No one could overlook the clown fig tree across the aisle from the miniature palm grove. When Rasmusson planted it in 1994, it was only four feet tall. Today it's five or six times that height, a mass of dazzling green and white foliage. "This area here was dark," Rasmusson recalled, so he wanted a bright plant that would catch visitors' eyes and lure them over to inspect its leaves, each one dappled with a unique green and cream pattern, as if hand-painted. The little figs it bears have the additional charm of resembling clown's noses. "Kids like that," Rasmusson said. But the tree had grown almost too tall. He planned to prune and thin it out soon. "We call ourselves plantsmen -- because we do everything."

Rasmusson directed my attention to another plant in that corner of the building: a hybrid philodendron that develops intriguing eyelike patterns on its main stem as the lower foliage falls out. A local plantsman by the name of Rudy Lasaga developed it, the nursery superintendent told me. Now deceased, Lasaga "was about 80 years old at the time I knew him, and he used to do lots of crossing of plant material. I had to beg to get this thing! Finally he told me he would give it to me as long as I promised not to give it to anybody else or cross it with anything."

Rasmusson wheedled and pleaded for other unusual specimens when he was replanting the conservatory. "I went to begonia people's homes. I went to palm people's homes." When the succulent bed was being developed, Root donated South African specimens she had collected at her home over the years. "I've given plants, too," Rasmusson said. "We all have our little babies in here. It's like an addiction we have, and we bring them in here to show them off."

As nursery supervisor, Rasmusson has a budget enabling him to buy material from outside suppliers. But many of the new flowers and shrubs and trees planted in Balboa Park are developed from seeds and cuttings at the park's Kate Sessions nursery. You could live in San Diego all your life and never notice the inconspicuous sign that marks the nursery's entrance just down the hill from the Frisbee golf course on Pershing Drive. The nursery occupies 8.3 acres, according to Kim Duclo, the veteran park ranger who accompanied Rasmusson and me on a tour on another recent morning. That's a quarter the size of the nursery Kate Sessions operated 110 years ago in the northwest corner of the park, near Sixth and Upas. Yet the current nursery feels huge; it's hard to imagine that the woman known as the mother of Balboa Park tended to anywhere near the variety of plant life that Rasmusson has under his purview.

Upon our arrival, he pointed out the ice that had formed in a puddle on the ground. "I've never seen it this cold here in San Diego," he said. In addition to the Moreton Bay fig tree seedlings, at least a dozen other plants had succumbed. But Rasmusson wasn't dwelling on the damage. Just promoted to the supervisory job the week before, he was bursting with ideas for upcoming projects. A small but immediate one was a remake of the south side of Zoo Place, the main road leading into the zoo parking lot off Park Boulevard. The zoo is responsible for the north side of the road, where its gardeners have established a lush and interesting mixture of plants. But only a few undistinguished-looking chitalpa and eucalyptus trees occupied the city-tended strip of dirt.

I'd passed the site any number of times without giving it a second thought. It didn't look disgraceful, just boring. But Rasmusson was itching to beautify it. He'd like all the park's plantings to make passersby halt in their tracks. "You want them to kind of look at it and think, 'Wow! I could do that!' or 'What is that plant?' " he said. He wanted the new Zoo Place plantings to "kind of match" the Desert Garden across Park Boulevard but also to tie in with plants on the north side of Zoo Place. As the zoo's gardeners had, he wanted to plant New Zealand tea trees and Westringia rosmariniformis (an Australian shrub that's a common fixture of the San Diego landscape). But he also wanted to add new, complementary specimens. "There's some bottlebrush over there. But we have a weeping bottlebrush! I'll probably add that, so it'll be different but also the same. If we tie the whole thing together, it will really flow."

He'd planned to inject some color by planting yellow lantana, but the cold had killed the nursery's stock of it. Still, he had other candidates that he promised to show me. First, we walked through a large room filled with metal tables, the place where most of the nursery's cutting and potting take place. A large plastic bag filled with bright orange stems laden with shiny black berries -- nuts from the palm Chamaedorea tepijilote -- lay on one of the tables. Volunteers work at the nursery every Wednesday morning, and Rasmusson explained, "The next time they're here, we'll have them take off the seed coats and pot all these up, and we'll grow them on. And that'll be the future chamaedoreas in the park."

We zipped through several hothouses, where I glimpsed some of the ongoing experimentation. Rasmusson pointed out sprouts started from seeds that a member of the city's spray-crew had brought back from Florida. "It's one of those weird things that we've never seen before. So we decided to try growing it." On another table, the gardeners had started Malaysian red guavas. "We just did it for fun to see what it'll do," Rasmusson said. The hothouses also hold trusty standards that need a protected start in life, such as golden candles, a Central American native cherished for its glowing yellow bracts. Cuttings were growing in more than 100 four-inch pots, and gazing down at them, Rasmusson noted, "They're super-cold-sensitive. Luckily they're in here!" By September they would be transplanted into one-gallon containers and moved into one of the shade houses outdoors, to grow for another year or so before being displayed in the Botanical Building.

Good news and bad greeted Rasmusson on the series of tables outside the hothouses: the dead Moreton Bay fig sprouts and yellow lantana, dead ruellia. But a crowd of potted violas was unscathed, and the calendulas looked robust. Orange flags stuck out of some of the pots, a sign that the plants had been reserved to go to a particular spot in the park. Green flags signaled availability.

A park and recreation flatbed truck pulled up next to us bearing a young dragon tree (Dracaena draco) uprooted from Zoro Garden. A sinkhole had developed requiring repair work, and the dragon tree had fallen victim to the excavation. Rasmusson told the truck driver where to deposit the tree; it would be placed in a container until another permanent home in the park could be found.

He led me to the first of the nursery's two large shade houses. "This is where we have a lot of the plant material that we rotate to the Botanical Building and then bring back," Rasmusson said. "Here we have all our cymbidium orchids that will be the next display in the center circle. You can already see the buds." They'd be in full bloom before long, he promised. We stopped in front of more golden candles. Two or three times the size of the young plants in the hothouse, these had been cut down to bare stems, but soon their foliage would reappear. By late spring or early summer, sunny yellow bracts would burst forth. "But you see how these are getting really big?" Rasmusson asked. In another year or two, they'd crowd themselves out of their two-gallon containers. "So we'll plant them somewhere in the park, and the little guys inside will become our display plants."

In another aisle, Rasmusson pointed out a ground-cover plant that he was thinking about using at the Zoo Place site. "These are still small right now, but they have a real pretty purple flower." What appealed to him even more were the leaves -- round and grayish green. "It's a look that I don't see too often," he said. It could blend well with other specimens he was considering.

Later, in the nursery's tree section, I saw two of the trees Rasmusson was thinking about for the Zoo Place site, and his choices made me smile. One (Beaucarnea recurvata) is commonly known as the elephant-foot tree because of the pachydermatous appearance of its rough gray trunk base. (Another of its common names is the ponytail palm, an allusion to the long, droopy foliage.) Rasmusson wanted to mix this in with Brachychiton rupestris, an Australian native that develops a rough gray trunk that's shaped like a bottle but calls to mind some body part borrowed from a giant of the animal kingdom. Both would contribute to "that zoo look," Rasmusson suggested.

He had very different ideas for the landscaping around the just-completed House of Spain, the newest of the park's international cottages (and the last one likely to be constructed). Although each of the cottages has a cultural theme, the grounds around each house were never used as a showplace for flora from that part of the globe until the House of Puerto Rico was built in 2005. Rasmusson pointed out that the nursery had a nice stock of Caribbean plants that would complement the national theme. He got permission to develop a design that used many of them, and now he was planning something similar for the House of Spain. "Definitely got to have a cork oak!" he declared. "And we have to have an olive tree! Got to have the bay laurels, because they have a lot of that over there. I could put a couple of strawberry trees in there, too, because that's also a Mediterranean thing." He'd work on the shrubs and flowers once he got the big elements in place.

After we concluded the informal tour, Duclo and I drove to the park's Administration Building, where the rangers are based. Duclo has worked as a ranger for more than 11 years, and his knowledge of the park's history is encyclopedic. He thinks one of the themes that runs through that history is how big an impact certain individuals have had on the park at various times. George Marston was such a figure, as was Kate Sessions. Kathy Puplava (the park's first horticulturist, now retired) was another. "Even though we do things collectively, individual people can have a vision," Duclo commented to me, "particularly if they're really plant-knowledgeable people like Mike [Rasmusson]." Duclo thinks, "We're coming into a renaissance for the park now. We've got a couple of people in place like Paul Sirois and Mike that really have a vision for the next 100 years. And it'll be great, because it's looking at what fits and what works."