Garden tips: Funnel ants; Dorrigo waratah; moth orchid; mulch

Funnel ants are taking over the lawn volcano-like mounds.

Moth orchids need a brightly lit position without direct sun.

After rain we get soil pyramids on our lawn during the night that are 3cm-7cm high with a hole in the middle. What causes these? What could I put down the hole to fix the problem? - M. SIGEL, BRISBANE

Funnel ants are common in Brisbane, forming volcano-like cones, especially after heavy rain. They prefer sandy soil and can form extensive underground nests. Try products such as Ant Sand, but large infestations may need a professional pest controller. Small mounds of mud balls after rain are due to earthworms, so leave those be. In Victoria and Tasmania, taller “chimneys” of soil are the work of land yabbies or land crayfish.

I was given a gorgeous moth orchid (Phalaenopsis) for my birthday but the leaves are going limp and losing their lustre, and it doesn’t look happy. What’s wrong? - ANNA WHITEMAN, SYDNEY

It’s easy to overwater these lovely houseplants. The roots will rot if water sits in the saucer or base of the pot, causing the leaves to collapse and the plant to die. It needs a brightly lit position without direct sun. Water when it begins to dry out, perhaps twice a week in summer.

I have shredded the lighter branches and foliage of a pussy willow that has been felled. Is it safe to use this immediately as mulch around my established citrus trees? - TIM KAETHNER, CRAFERS, SOUTH AUSTRALIA

Woody mulches draw nitrogen from the soil as they decompose but green foliage adds some nitrogen. An equal mix is probably OK to use but mostly woody material should be composted first or supplemented with some pelletised poultry manure. However, willows are notorious for their ability to grow from small pieces, so there is a risk the mulch could start shooting. Hot composting is recommended to avoid this. All willow species except weeping willow and two sterile hybrid pussy willows are weeds of national significance.

Where a three-in-one fruit tree has particularly strong or weak growth on one of the varieties, what action would you recommend to get a more balanced harvest? - BOGEY MUSIDLAK, CANBERRA

When several different varieties are grafted on to the one tree, pruning is essential to keep them all in balance. The most vigorous will overwhelm the others if not kept in check. Thin out excess branches and keep each variety confined to its own area. Timing will depend on what fruit types they are.

Send questions to: [e-mail] Helen Young, PO Box 3098, Willoughby North, NSW 2068. Website: helenyoung.com.au. The best question for December wins a signed copy of The Australian Native Garden by Angus Stewart and AB Bishop, worth $50.

FLORA:Dorrigo waratah (Alloxylon pinnatum) is a lesser known but spectacular flowering tree that adds crimson to the garden around Christmas. Native to the high country around Dorrigo, in northeastern NSW, it forms a small evergreen tree in cultivation with dark, glossy leaves. It grows in a range of climates from subtropical to cool, even as far south as Tasmania, but can be difficult to establish. Rich, deep, well-drained soil and a sheltered position are ideal. The wheel-like flowers can appear from spring through to autumn and attract bees, birds and other insects. They also make good cut flowers. The pinkish red timber from this species is excellent for furniture and cabinet making.