Tristaniopsis
( tris - TAN - ee - op - sis )
At-A-Glance Information
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This species of evergreen trees and shrubs needs full sun and regular water, and are native mainly to Southeast Asia, New Guinea, New Caledonia, and Australia. They are commonly called Water Gum or Kanuka, and are slow-growing to between 20 and 30 feet tall in most gardens with a spread of 10-20 feet. Fragrant yellow flowers bloom in springtime through early summer, and are attractive to bees and other pollinators. Leaves are glossy and dark green, and trees form dense, rounded canopies that provide excellent shade. Use these trees to add elegance to urban landscapes, as a specimen tree for its beautiful blooms, or as a shade or street tree. They are also fantastic for erosion control, bioswale or rain garden plantings, and as urban trees that can take a lot of pollution.
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Tristaniopsis species and varietals
The genus Tristaniopsis is a member of the plant family Myrtaceae and includes around 45 species. These trees perform best in zones 15-24 (to find your zone, click here: Zone Map).
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Tristaniopsis collina (Hill Water Gum, Hill Kanuka) This species is native to eastern Australia, and forms a small to medium-sized tree to about 115 feet tall. Trunks are irregular, and greyish to cream-colored. Branchlets are purple. Flowers are yellow and bloom from November through January in the plant's native range. Dry seed capsules follow, and mature from April through July. |
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Tristaniopsis exiliflora (Kanuka Box) This species is native to Queensland, Australia, where it grows alongside streams and rivers. Kanuka Box can reach 66 feet tall, and have a slow growth rate. Trees will resprout freely if the main trunk is damaged. Crown is dense and spreading. These trees are harvested for their timber in their native range. |
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Tristaniopsis laurina (Tristania laurina) (Water Gum, Kanooka) These Australian natives have dense crowns filled with glossy green, narrow foliage. They reach 45 feet tall and 30 feet wide at maturity. Bark is mahogany and peeling, revealing satiny white bark underneath. Flowers bloom in clusters in late spring and early summertime and are fragrant, yellow, and profuse. Blossoms are followed by seedpods. Use Water Gum as a tall screening plant, or as a boundary or background planting. They also do well in large containers. Variety 'Elegant' has broader leaves than the species and emerge red, maturing to green when shaded. Other cultivars include 'Luscious' and 'Hot Tips'. |
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Caring for and pruning tristaniopsis Trees
Plant Tristaniopsis trees in a place in the landscape that will receive full sun to light shade. Growth and flowering potential are maximized in full sun exposure (between 6 and 8 hours of sun each day). Younger trees may appreciate some late afternoon shade in warmer climates. Ensure that soil is well-draining before planting. If local soils are particularly clayey or compacted, it is suggested that the planting area is amended with plenty of organic material and/or sand before installation. They can tolerate a wide variety of soils, including sandy loams, clay loams, and well-draining rocky soils. They are also very hardy trees for most landscapes, being frost, flood and drought tolerant. After installation, apply a thick layer of mulch around the base of trees to suppress weed growth, increase soil moisture retention, and help to regulate soil temperatures. Water newly planted trees regularly to help them establish a strong root system. Mature trees are considered to be drought-tolerant, getting by on precipitation alone for most of the year. They do appreciate deep waterings during extended periods of drought, however.
Prune simply to shape trees; they have a handsome natural canopy shape and really do not need much pruning. They can have a tendency to produce foliage growth at their base, which can be removed in late winter or early springtime. Prune young trees to encourage a strong central leader to emerge. Apply a dressing with an organic compost once a year in springtime to support the season's growth and flowering. This is typically sufficient for trees as far as fertilizing goes, however if trees seem to be struggling (not growing well or with discolored leaves), they may benefit from a feeding with a balanced, slow-release fertilizer applied in springtime.
Prune simply to shape trees; they have a handsome natural canopy shape and really do not need much pruning. They can have a tendency to produce foliage growth at their base, which can be removed in late winter or early springtime. Prune young trees to encourage a strong central leader to emerge. Apply a dressing with an organic compost once a year in springtime to support the season's growth and flowering. This is typically sufficient for trees as far as fertilizing goes, however if trees seem to be struggling (not growing well or with discolored leaves), they may benefit from a feeding with a balanced, slow-release fertilizer applied in springtime.
Propagation
Tristaniopsis can be propagated either by using cuttings or from seed. To ensure that your propagated plant will have the exact same qualities and characteristics as the parent plant, use the cutting method. If you would like to experiment and see what plant you can grow from seed, just keep in mind that it will not necessarily be the same as the parent plant. To propagate your Water Gum tree, follow the instructions below:
Propagating Tristaniopsis by Cutting
Propagating Tristaniopsis by Seed
Propagating Tristaniopsis by Cutting
- Gather your materials. You'll need a clean, sanitized, sharp pair of garden shears, rooting hormone, a pencil, and a 3-inch pot filled with well-draining compost or other organic material. If you don't have any potting medium on hand, you can make some. Just mix together equal parts (by volume) moss peat and horticultural-grade sand or grit sand.
- In spring or early summertime, choose the plant that you'd like to propagate. Ensure that this plant has had a good watering the night before, as this will improve the chances your cutting will take root. Cut one or more 6 inch softwood portion(s) of the end of a non-blooming branch and strip the leaves off of the lower half. Make a hole in your planting medium by pushing your pencil into the soil. Dip the end of the stem in rooting hormone, and plant it in your pot. Fill in soil around the cutting to support it, but do not pack it down too much.
- Moisten with water, and ensure that the pot has good drainage. Your pot should be kept in warm, sunny conditions indoors (and not in direct sunlight). Water whenever your soil is dry under the top layer. After about four to six weeks have passed, your cutting should be rooted. When you notice new growth, you'll know you have roots.
- Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 55 and 70 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, until the next spring, when you can transplant it to its new home. Ensure that the last frost of the year has occurred before doing this, as it can seriously damage your new shrub.
Propagating Tristaniopsis by Seed
- Keep in mind that the plant you get from seed will not necessarily mimic all of the characteristics of the parent plant. To propagate by seed, you will need a paper bag, a pot or tray filled with well-draining compost or other organic material, a spray bottle and a fork. If you don't have any potting medium on hand, you can make some. Just mix together equal parts (by volume) moss peat and horticultural-grade sand or grit sand. You will also, after a few weeks, need individual 3-inch pots for each seedling that grows.
- Harvest your seeds. They are contained inside of the 1/4 inch to 1/2 inch diameter dark brown to dark reddish-brown seed capsules produced by trees in late summer or fall.
- Water your prepared seed tray or pot filled with soil, and ensure that good drainage is occurring. Place your seeds in your prepared pot or seed tray about a quarter inch to a half-inch under the soil surface. Cover them with soil and water with your spray bottle. Place your tray of seeds in a warm area that receives bright, indirect light. A greenhouse is the most ideal climate, but a planting tray inside a window will do as well. Germination usually takes 3-4 weeks from sowing. Once you begin to see seedlings sprout and they are able to be handled, transplant them to their own individual 3-inch pots, filled with the same potting medium as described in Step 1. Loosen the seedlings from the potting medium by digging down with the tines of your fork about an inch and a half, gently working the seedling up until it is out. Then, replant the seedling in its individual pot.
- Keep the seedling's potting medium moist, but not wet, by spraying the soil with your spray bottle. Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 55 and 70 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, until the next spring (after the danger of frost has passed), when you can transplant it to its new home.
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Tristaniopsis seed pods ready to release seeds. |
Problems and Pests
Tristaniopsis trees typically have issues with the following pests and diseases:
- Scale Insects
- Leaf Hoppers
- Leaf-Eating Beetles
Gallery
Tristaniopsis flowers are yellow and bloom from spring through summertime.
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These trees have handsome foliage that lasts year-round.
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Tristaniopsis trees make wonderful shade, street, and parking lot trees.
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Videos
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A quick video about a choice garden varietal of Tristaniopsis.
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Learn about these great landscape trees.
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Resources
The New Sunset Western Garden Book: The Ultimate Gardening Guide (2012) - Page 638, Tristaniopsis laurina (Water Gum)
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