How plants can show us what lies beneath

A geologist learned this eucalyptus torquata grew in soils over rocks associated with nickel sulphide deposits. It’s a practice known as geobotany.

Eucalyptus torquata, commonly known as coral gum or Coolgardie gum.

Following mention of the coral gum, Eucalyptus torquata, in this column in April, a reader made contact offering some fascinating information. John Earthrowl, a retired exploration geologist, recalls working for an international exploration company in Western Australia during the nickel boom of 1967-1970. His team learned that Eucalyptus torquata only grew in soils over rocks associated with the nickel sulphide deposits they were looking for, so they used that species as a marker. It’s an exploration tool known as geobotany.

Earthrowl took it one stage further, observing thatthe showy flowers of E. torquata attracted flocks of certain local bird species, especially in the early mornings, so he added binoculars to his daily work kit. Dubbing the practice geo-ornithology, Earthrowl notes: “It is not a recognised tool of the mineral explorationist but I have always maintained that a good explorationist is a geologist with interests in nature beyond rocks and minerals.”

Despite the coral gum’s limited distribution in the wild, it has proven adaptable in cultivation where summers are dry, and is now popular for gardens, parks and streetscapes.

All that jazz

The Celebrations range of kangaroo paws offer vibrant colour combinations on naturally compact and bushy plants.

Celebrations Jazz.

Celebrations Carnivale.

‘Jazz’ is the latest in the range, which are best suited to growing in pots in full sun. The cut flowers have a vase life of two weeks.

Celebrations Aussie Spirit

Celebrations Masquerade.

Q&A

Our garden is densely planted, with some large conifers and Norfolk Island pines. How can we easily improve the soil quality, apart from adding autumn leaves and compost?

Robin Nettleton, Melbourne

Home-made compost and decomposed autumn leaves are two of the best items to improve your soil and replenish organic matter. You can apply them to the soil surface, as water and earthworms will incorporate them. Also excellent are worm castings, seaweed products and soft mulches such as sugar cane mulch, pea straw and lucerne. Microbial products such as Popul8 and SoiLife can also help. Regularly test the soil pH and maintain it between 6 and 7.

Our magnificent 20m-tall Norfolk pine is home to all sorts of creatures and gives wonderful shade. But it’s hard to grow plants under it that cope with the roots, needles and our sandy soil. What tree with contrasting foliage might work?

Ruth Kennedy, Melbourne

These conditions are very challenging. With some sun, you could try a variegated willow myrtle (Agonis flexuosa ‘Variegata’) or weeping river wattle (Acacia cognata ‘Lime Magik’), both natives with weeping form and bright foliage. Pin cushion hakea (Hakea laurina) is another possible native. Tough, large shrubs include black elderberry (Sambucus nigra ‘Black Lace’), mist flower (Bartlettina sordida) and variegated silverberry (Elaeagnus ‘Limelight’).

Is it possible to strike shoots that grow from the trunk of a ponytail (Beaucarnea recurvata)? I’ve tried removing some with some bark attached but haven’t had success.

Trevor Sauer, Brisbane

Also called elephant’s foot, Beaucarnea recurvata has a swollen trunk base that can spread up to 3m across. Shoots near the base usually have some roots and can be separated fairly easily. For shoots on the trunk, use a sharp paring knife to cut them away in spring, remove the bottom leaves, and let dry for a week or so. Dip in rooting hormone then pot into cactus mix and water sparingly.

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