Stenocarpus

( sten - oh - CAR - puss )

At-A-Glance Information

This genus of shrubs and trees produces individual plants with variably shaped leaves and eye-catching flowers. These tropicals need full sun and moderate to regular water to flower and perform well in the landscape. Species produce flowers in shades of orange, red, yellow, and white and are often fragrant, sometimes described as rank, pungent, or off-putting. They form large shrubs or trees, typically reaching up to 25 to 40 feet tall and 12 to 25 feet wide at maturity. Use these plants as focal specimens, screening plants in narrow spaces, or as street or urban trees. They are commonly included in wildlife, container, informal, and tropical gardens. Take care when planting Stenocarpus in the landscape, as sap and other plant parts can cause contact dermatitis.

Stenocarpus species and varietals

The genus Stenocarpus includes around 22 species and is a member of the plant family Proteaceae. The plants in this genus are related to those in Banksia, Embothrium (Chilean Firebush), Hakea (Pincushion Tree), Grevillea (Spider Flower) and Macadamia. These trees and shrubs grow best in USDSA hardiness zones 9-11 or Sunset growing zones 16, 17 and 20-24. To find your zone, click here: Zone Map.

Stenocarpus angustifolius (Narrow-Leaf Stenocarpus)
These shrubs or small trees typically reach between 13 and 16 feet tall when mature and have narrow, lance-shaped leaves. Flowers are creamy-white and bloom from August to December in the plant's native range (Queensland, Australia). Fruits appear in December and contain winged seeds. Cultivars of this species include 'Doreen' (compact shrub or small tree with creamy curly flowers), 'Forest Lace' (grown as a foliage plant for the cut flower industry) and 'Forest Gem' (commercially grown for cut foliage).

Stenocarpus cryptocarpus (Giant-Leaf Stenocarpus, Giant-Leaf Stenocarpus)
This species is endemic to north Queensland, Australia. These trees form buttress roots at their bae, and can reach up to 82 feet tall when mature. Flowers are cream-colored and strongly fragrant, blooming from December through April in the plant's native range.

Stenocarpus cunninghamii (Little Wheel Bush)
This species is endemic to northern Australia, and has narrow lance-shaped leaves. These trees or shrubs can reach up to 40 feet tall when mature, and produce pale yellow to white flowers in March to May. These plants love dry climates and are perfect for drought-tolerant beds or xeriscaping.

Stenocarpus davallioides (Fern-Leaved Stenocarpus, Fern-Leaf Stenocarpus)
This species is endemic to northern Queensland, Australia, and forms a large canopy tree that reaches up to 130 feet tall when mature. Flowers are cream to greenish and leaves are fern-like (deeply divided). This species is rarely cultivated as a garden ornamental due to its large size. 

Stenocarpus reticulatus (Black Silky Oak)
This species is endemic to northern Queensland, Australia, and forms a tree with strongly-perfumed creamy-white flowers. The flower scent is described as unpleasant, meant to attract nocturnal moth pollinators. These trees typically reach about 115 feet tall when mature, making them large shade or canopy trees better for larger landscapes.

Stenocarpus sinuatus (Firewheel Tree, Tulip Flower, White Beefwood, White Oak, White Silky Oak, Queensland Firewheel Tree, Queensland Fire Tree, Wheel of Fire, Tulip Tree, Rotary Tree)
These are slow-growing trees that have dense foliage and reach 30 feet tall and 15 feet wide at maturity in most cultivated landscapes. Leaves are shiny and deep green and flowers are tubular, red and yellow, arranged in clusters that resemble the spokes of a wheel (hence the common name). They make showy trees for patios or terraces and can add a tropical look around swimming pools and in lawns.

Caring for stenocarpus

Take care when planting Stenocarpus in the landscape, as sap and other plant parts can cause contact dermatitis. Grow Stenocarpus in a sunny location in well-draining soil that is acidic to neutral and low in phosphates. Provide shelter from frost and high winds. Space plants between 15 and 33 feet apart to allow for their mature size; if growing as a screening, plant between 6.5 and 10 feet apart. Stenocarpus prefer well-draining, somewhat poor soil that has a pH of between 5.0 and 7.0 (acidic to neutral). If local soils are particularly poor in nutrients or do not drain well, make sure to amend the planting area with plenty of organic compost before installing. Apply a layer of mulch around the planting area to suppress weed growth, maintain consistent soil temperatures, and to increase soil moisture retention.

Water new plantings regularly as they establish a strong root system in their new home. At maturity, these shrubs and trees are considered to be quite drought-tolerant, able to get by for much of the year on rainwater alone with supplemental irrigations during extended periods of drought. As a general rule of thumb, water deeply when the top 2-3 inches of soil feels dry to the touch. Avoid overwatering, which can quickly lead to root rot issues. These trees and shrubs are well-adapted to poor soils, and do not generally require fertilization. Stenocarpus can be pruned as needed to maintain shape and size, and to remove dead, dying, damaged, crossing or diseased branches. Prune to shape; otherwise allow these shrubs to take their natural form. Stenocarpus are typically long-lived if given proper care, and can survive in the landscape for decades to a century or more before needing to be replaced. In harsh urban environments or cultivated landscapes, their life span is shortened to between 50 and 80 years.

Propagation

​Stenocarpus, or Firewheel Tree, 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 shrub, follow the instructions below:

Propagating Stenocarpus by Cutting
  1. 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. A good substrate for propagation of cuttings is a light blend of 1/3 pasteurized soil or compost, 1/3 sand, vermiculite or perlite, and 1/3 coconut coir or peat moss.
  2. 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 portion(s) of the end of a non-blooming semi-hardwood 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.
  3. 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.
  4. 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 Stenocarpus by Seed
  1. 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. The best potting medium for seed germination is a light blend of 1/3 pasteurized soil or compost, 1/3 sand, vermiculite or perlite, and 1/3 coconut coir or peat moss.
  2. Harvest your seeds. The seed pods on Stenocarpus plants are pretty easy to spot, they're large and left behind after flowers have faded. Once they have dried out and begun to split open, you can harvest the seeds inside. Cut them off of the plant, placing them in a paper bag. Harvest as many as you can, and place the paper bag in a dry, cool, dark area. They will begin to split open and release the seeds contained inside. Once they have been released, take them out of the bag and put them in a container so you can work with them.
  3. 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 10 to 30 days (2 to 6 weeks) from sowing.
  4. 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.
  5. 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.
Stenocarpus trees and shrubs produce seeds within woody capsules that split open at maturity. Each contains dozens of overlapping seeds.
Stenocarpus seeds are flat, light, and tan to brown, equipped with a terminal wing that aids in wind dispersal.

Problems and Pests

Stenocarpus trees and shrubs, although typically resilient in most landscapes, can be susceptible to developing issues with the following pests and diseases:
  • Root Rot
  • Nutrient Sensitivity
  • Fungal Blight (Sclerotium rolfsii)
​

Gallery

Stenocarpus flowers are eye-catching, and can be red to yellow or white.
These trees are beautiful when admired from below, and are commonly planted along patios.
Stenocarpus make great privacy screening.

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Resources

Tree on Fire: Stenocarpus sinuatus
Wikipedia: Stenocarpus
The New Sunset Western Garden Book: The Ultimate Gardening Guide (2012) - Page 613, Stenocarpus sinuatus