Eucalyptus Babies

Posted at 9:08 am July 15, 2009 by Christy Powell

We grow over 30 types of Eucalyptus to feed our koalas. These are two-week-old Eucalyptus camaldulensis seedlings.

We grow over 30 types of Eucalyptus to feed our koalas. These are two-week-old Eucalyptus camaldulensis seedlings.

Some new babies are growing in the San Diego Zoo’s plant propagation nursery: Eucalyptus trees! As many people know, koalas eat mainly Eucalpytus leaves, and part of my job as a plant propagator is to grow food for the animals. These seedlings will eventually be planted at a browse farm off site where the trees are grown in rows and cut back to maintain the new, juvenile leaves the koalas love.

We are propagating 13 of the most preferred Eucalyptus species, including Eucalyptus camaldulensis, Eucalyptus puntata, Eucalyptus rudis, and Eucalyptus robusta. A majority of theses species are not commonly available for purchase from nurseries, so that’s why we start the seeds in a greenhouse nursery. The seeds are sown in “conetainers,” which are long cylindrical containers that slide into trays. These specific containers allow the trees to establish good root development without the circling that occurs in some shallower pots. Each tray holds 200 containers that can be moved around and grouped together as the seeds germinate.

Eucalyptus seeds are very small; 1,000 seeds weigh about 1 ounce!

Eucalyptus seeds are very small; 1,000 seeds weigh about 1 ounce!

The containers are first filled with a light propagation mix soil. Then the small Eucalyptus seeds are sprinkled on the surface of the soil. Finally, a layer of sand is added to cover the seeds, and they are watered in and misted once a day. The seeds germinate pretty readily; the ones sown on June 22 were already sprouting just six days later. The seedlings are now being transitioned from the greenhouse to a protected area in the nursery. Once the seedlings are large enough, they will be shifted to a larger container called a treepot (containers that are longer than they are wide). By spring 2010, the babies should be able to leave the nursery and settle into their new home at the browse farm. It will take several more years before browse will be able to be harvested from these new seedlings.

The San Diego Zoo has the largest koala population (11 currently at the Zoo, plus a dozen more on loan to other zoos) and the most successful koala breeding program outside of Australia. We were the first zoo in the United States to welcome a koala joey. The San Diego Zoo is fortunate to have such an ideal climate for growing fresh Eucalyptus for the koalas, because they eat a lot of it! Koalas eat about 1 to 1.5 pounds (454 to 680 grams) of leaves each day, which doesn’t include the several species they are offered but might not eat. Eucalyptus leaves are poisonous to most animals, but koalas have special bacteria in their stomachs that break down the toxic oils. Special cheek teeth grind the tough leaves. Koalas don’t get many calories from their diet, but they conserve energy by moving slowly and by sleeping as much as 20 hours each day.

The San Diego Zoo received its first two koalas, Snugglepot and Cuddlepie, in 1925, as a gift from the children of Sydney, Australia, to the children of San Diego. Koalas have few natural predators, although sometimes a dingo or large owl can take one. The most common direct causes of koala deaths are from motor vehicles and dogs. So they are definitely safest high up in trees. In the past, koalas were killed for their coats. In fact, from 1919 to 1924, eight million koalas were killed. Today, the koala is threatened by predation by domestic dogs and by a disease that has spread through most of the population. Unfortunately, some koalas get run over by cars. But the one thing that koalas and other wildlife can’t protect themselves against is the loss of their habitat. A combination of cooperative managed-care propagation programs, research, and support for habitat conservation projects continue to ensure the survival of koalas.

Christy Powell is a plant propagator at the San Diego Zoo.

Read more about the Zoo’s gardens

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5 Responses to “Eucalyptus Babies”

  1. nancy from michigan says:

    Christy, thanks for all the interesting information on growing eucalyptus leaves for the koalas. how many years ago did you start growing your own eucalyptus? I wouldn’t think that it would take sooolong.

    wow! it’s quite a process isn’t it? SDZ is some remarkable zoo growing it’s own food when possible for it’s animals. I understand that several varieties of bamboo are also grown for the pandas. what other things are grown for the animals at your zoo? it is so nice that so much information is shared with everyone even though we are not staff, keepers, or zoo workers in other areas. but, non the less, we are interested zoo lovers and animal lovers who like to keep abreast of what’s happening throughout the zoo in many different areas of expertise. thanks to these wonderful posts from everyone, we learn alot!!

  2. Christy Powell says:

    Hi Nancy,

    You’re welcome! Thanks for your interest in our browse program at the Zoo. I talked with the Curator of Horticulture at the Zoo and he told me that the browse farm was started in 1971 and that next year was when fresh food began to be fed out to the animals. In the mid ’70s he was working in the nursery and spent most of his time growing and raising up Eucalyptus for the browse program. He estimated that they had close to a million Eucalyptus seedlings growing at one time in the nursery.

    The pandas do enjoy 25 different types of bamboo and eat as much as 84 pounds of it a day! Other species we use for browse for the animals include Acacia for giraffes, Hibiscus and willow for primates, blackberry leaves for the insect house, and Ficus and bananas for the gorillas. There are eight full-time browse workers that collect the material and bring it to the keepers to feed out to the animals. There is always something new for me to learn working at the San Diego Zoo, and it is fun to share the botanical side of the Zoo with others.

  3. David G. Signer says:

    Are all the species commonly known as eucalypti actually members of the genus Eucalyptus?

    If there are eucalypti from other genera, are any non-Eucalyptus species fodder for koalas?

  4. Lucas says:

    Does eucalyptus make for good lumber? I don’t think I’ve ever seen a any furniture made out of this particicular trees. Also, would eucalyptus wood be a decent firewood?

  5. Christy Powell says:

    Thanks for your questions, Lucas. I am not a woodworker and haven’t worked with Eucalyptus lumber personally, but from what I understand, Eucalyptus wood is harder to work than other woods and has irregular grain. It also depends on the species of Eucalyptus. Some is as soft as pine wood, while other species are very hard. We had a Eucalyptus removed from my house, and we gave some wood to a person that makes bowls out of it. Eucalyptus wood is a decent firewood and burns well once dried. The remaining portion of the Eucalyptus tree we had removed was picked up for firewood.

    “The Eucalyptus in California” by Norman Day Ingham, Agricultural Experiment Station publication from 1908, is an interesting publication discussing the history of Eucalyptus in California and the potential uses for it if you would like to read more.


    Christy Powell