She Oaks versus Silky Oaks

Casuarina grove in Sydney Park

I confess to not liking She oaks (Casuarina) much. I quite like their needle-like leaves & even their appearance. Despite that I think they have more negatives than positives I will write about their attributes as unbiased as I can.

The Casuarina has around 60 different varieties.  They are often described as a shrub, though I cannot see why.  They grow to varying heights, but most reach around 10 – 20 metres.  Its growth is straight up & does not have a cascading form.  Their leaves are called cladodes, they are long segmented branchlets that look like pine needles.  Each segment is a leaf.

Casuarina leaf debris

These leaves drop & form a thick blanket around the tree & anything other than a Casuarina won’t grow.  You can manage to keep shade-loving plants under a Casuarina as long as you remove the fallen needles. Having lived with these trees I can say from experience that if you leave this job longer than a week, it becomes a big job as the needles will literally bury your plants.

Developers like to plant Casuarinas at new housing developments because they grow very fast & need no care.  They can reach a good height within 3 years & they thrive in very poor soil & semi-arid areas so they can cope with only the water from any rain.  The leaf debris also prevents any weed growth.

Casuarina sends out suckers from which new trees grow. These are hard to remove, but can be mown over

The Casuarina grows extensive root systems & is excellent in binding sandy soils & dunes to prevent erosion.

Casuarinas produce hundreds of small woody fruit that look like small spiny cones.  These cones are very dense & will not break if you tread on them.  The Glossy Black-Cockatoo (also known as the Casuarina Cockatoo) eats the unripe Casuarina cones, though I don’t think this bird hangs around Marrickville LGA.  Wood turners like Casuarina timber.

On Marrickville Council’s side of the Cooks River the Casuarina is the main species of tree because they are indigenous to this area.

The Silky oak, (Grevillea robusta, the Southern Silky oak or the Australian Silver oak) is the largest Grevillea of its species. Native to eastern coastal Australia, it’s a fast growing evergreen tree growing to 18 – 35 metres tall. Its growth is conical & it does not have a cascading form.  Its girth can grow to more than a metre making it excellent at carbon sequestration.    Its leaves look like fern fronds, grow to a length of 15-30 cm & are dark green.   The underside of the leaves is either grayish-white or rusty-red coloured.

This tree is rare because of over logging.  Furniture makers & wood turners love its beautiful timber.

Grove of Silky oaks in Bicentennial Park Rockdale

Grevillea robusta becomes literally festooned with fantastic golden-orange flowers that can be as much as 15 cm long in the spring.  The flowers last for many months & are filled with nectar making them a valuable food source for birds & flying foxes. It is also attractive to honey bees.

This tree does drop a lot of leaves, but unlike the leaf debris from a Casuarina, the leaves can be composted or laid directly as mulch on your garden.

Some people like myself can get contact dermatitis from touching the leaves.  If I wanted this tree in my garden, I would simply minimize contact with the leaves until it had grown to a good height.  You can easily keep kids away while it is growing if they show sensitivity to the leaves.  Because this tree grows straight upwards, the offending leaves get to above head height quite quickly.  The leaves that have fallen to the ground do not create itchiness as far as I know.

I’d like to see some Grevillea robusta planted both in parks & as street trees by Marrickville Council.  I have seen this done by Kogarah Council & the trees look stunning.  There is a grove in Bicentennial Park right next to a grove of Casuarinas making it very easy to compare the 2 species.

As far as I am concerned, the Silky oak beats the She oak hands down.  The Silky oak is a better looking tree, produces less debris, its leaves are suitable for compost, it produces tons of vibrant flowers for many months, it’s shade-producing & a prolific food producer for wildlife & honey bees. Perfect.

The Silky oak produces masses of golden flowers. You can see why wildlife love these trees