Garden tips: dendrobium beetles; propagation; azaleas; agapanthus

The native pink rock orchid, now renamed Thelychiton kingianus, is a target of dendrobium beetles.

Dendrobium beetles are orange and black, and about 10mm long.

A pest that destroys the new shoots is again attacking my Dendrobium kingianum. I’ve noticed a small caterpillar and an orange-and-black beetle. How can I treat the problem?

ANTONIA STEWART, SYDNEY

The native pink rock orchid, now renamed Thelychiton kingianus, is a target of dendrobium beetles. These are orange and black, about 10mm long, and eat the new leaves in summer. They then lay eggs that hatch into white larvae that can destroy all the growing tips and flowers. No products are registered to treat this pest but expert Jeff Howes, in a recent blog on gardendrum.com, suggests a way to catch them, using one hand to grab and the other held below for a second chance as they drop.

I’m getting bored purchasing plants from the nursery but increasingly amazed with the array of native plants in my local area. Can you share any advice on propagation for an intermediate gardener wanting to step it up a notch?

MICHAEL CAMERON, ALBANY, WESTERN AUSTRALIA

You do indeed have a wealth of beautiful native plants in your area. Two books to assist are Angus Stewart’s Let’s Propagate! and Jackie French’s New Plants From Old . The Australian Native Plants Society at anpsa.org.au has links to a range of resources related to propagation. It also has study groups for particular genera, such as Banksia and Grevillea. You could also join the Wildflower Society of Western Australia to meet fellow enthusiasts and experts; it has a branch in Albany.

My potted mollis azalea gets moved from place to place. It doesn’t flower every year. How can I get a glorious display of colour every year?

BOGEY MUSIDLAK, CANBERRA

These deciduous azaleas need a cold climate and cool root run. Although they grow in pots, in small or dark-coloured pots the roots can get too warm. Plant out yours in a semi-shaded position with moist, rich soil and good drainage or keep potting it up into a larger, heavy pot using premium quality potting mix. Keep the pot cool and well watered. Keep mollis azaleas well mulched.

Should I cut off the agapanthus flower heads now they’ve finished? How far down?

STEVE BROWN, WOLLONGONG

Cut the spent flower stems right at their bases. This stops the plants wasting energy on producing seedpods and prevents unwanted seedlings spreading.

Send your questions to: [e-mail] or Helen Young, PO Box 3098, Willoughby North, NSW 2068. Website: helenyoung.com.au. The best question for January wins a set of five elegant, magnetic vases for your dining table, worth $72.95 from Independence Studios (isgift.com).

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