Q&A special: Your bumper problem solver
All gardeners have questions, and we got a swag of them at our Reader Lunch in February – far more than we could answer on the day. Here’s a selection of queries on everything from planting under citrus to managing nematodes, answered by our panel of experts who attended the lunch. Where supplied, names and suburbs are given.
WHAT, IF ANYTHING, IS SUITABLE FOR PLANTING UNDERNEATH CITRUS TREES? Joan, East Gosford, NSW
AYou can do this, but keep it to plants with shallow roots. I suggest annual alyssum, or perennial alyssum ‘Snow Princess’, which both flower over a long period and attract bees and beneficial insects. Small flowering annuals such as pansies or lobelia are suitable, as are shallow-rooted herbs. Try marjoram, oregano or thyme. All of these will do best on the outer edges of the canopy, where they can catch some sunshine. In the shadier spots, try some colourful impatiens. Just be sure to maintain a clear area at least 30cm in all directions from the trunk, so you can keep an eye on the graft union and ensure it remains healthy, while avoiding moisture build-up on the bark, which may encourage collar rot. To prevent damaging the citrus roots when planting, just pile compost on the surface and plant seedlings into that. Phil
WHICH PLANTS DO YOU RECOMMEND FOR SPOTS IN THE GARDEN WITH DRY SHADE? Barby, Wentworth Falls, NSW
AHere are some classic options to choose from, all of which are clumping plants that will multiply happily, even in dry shade: clivia ( Clivia spp.), aspidistra ( Aspidistra elatior), hellebores ( Helleborus spp.), Japanese windflowers ( Anemone x hybrida) and lamium ( Lamium spp.), such as Lamium ‘White Nancy’. Elizabeth
WHAT ARE THE BROWN SPOTS THAT APPEAR ON APRICOT TREE FRUITS, AND WHAT CAUSES SHOT HOLES IN THE LEAVES? Christine, Belair, SA
ASometimes this is called ‘freckle’, after the spots on the fruit, and sometimes ‘shot hole’ after the damage to the leaves, but it’s caused by the same thing. It’s a fungal problem, and it’s worse in some years than others. If we get a humid, wet spring, it tends to be worse, and some varieties are more susceptible than others. The fruit is still fine to eat, just not as aesthetically pleasing. If you want perfection, apply a copper-based spray at bud burst, but be aware that long-term use of copper is not good for the worms in soil. I don’t spray for that reason, and the same with leaf curl on my peaches, but our climate is predominantly dry, whereas growers in more humid areas may have to spray. Keeping trees strong and healthy improves resistance, although it doesn’t mean you won’t get it at all. Sophie
PELARGONIUMS, COMMONLY CALLED GERANIUMS, REQUIRE ACIDIC SOIL. HOW DO I MAKE SOIL IN A HANGING BASKET ACIDIC? Carolyn, Berry, NSW
AThey’re not really that particular, however if you want to make the soil more acidic, mix in some compost, and mulch with pine needles. Elizabeth
I HAVE A PUMPKIN VINE AND THE PUMPKINS KEEP ROTTING WHEN LITTLE. WHAT CAN I DO? Judy, Riverview, NSW
AIt’s more than likely that the female flowers haven’t been pollinated. Female flowers on plants such as pumpkins and zucchinis have swollen bases that look like tiny fruit, while the males don’t. When they are not pollinated, these tiny fruits brown, then drop off. You can always help by using a small artist’s brush to collect pollen from a male flower, and gently dab it into the centre of the female. This is best done in the morning. Regularly pollinating the flowers in this way will ensure much greater returns. It’s also beneficial to grow flowers among your vegies to attract lots of natural pollinators, such as bees. Keep in mind, too, that pollination can also be adversely affected by very hot or wet weather. Judy
IS IT BETTER TO USE SUGARCANE MULCH OR PEA MULCH AROUND THE GARDEN?
AThese are both great options, so it really depends on what you want from a mulch. Pea straw breaks down fairly quickly – within three months or so – adding nutrients and organic matter to the soil. Sugarcane mulch takes about six months to break down, and it conditions the soil, but is not as rich in nutrients. If you just want an easy-to-handle, long-lasting mulch for a vegie patch or flower border, choose sugarcane. If you would like to increase fertility, then go with pea straw. Phil
WHAT IS A GOOD EVERGREEN TREE ABOUT 2M HIGH TO PROVIDE SUMMER SHADE FOR HELLEBORES? THE POSITION FACES WEST. Chris, Drummoyne, NSW
AYou really need a shrub that you can prune into a tree shape, so it develops a clear trunk and doesn’t obscure the hellebores. In your area, I’d suggest either a sasanqua camellia or a glory bush ( Tibouchina spp.). Tibouchina ‘Noelene’ is particularly attractive, because the flowers change from white to pink and mauve shades, deepening as they age. If you prefer native plants, I would recommend a lemon-scented tea tree ( Leptospermum petersonii) or the lillypilly Syzygium ‘Cascade’. Judy
CAN YOU TRANSPLANT A MATURE CITRUS TREE EITHER INTO A POT OR TO ANOTHER PLACE IN THE GROUND? IF SO, WHAT ARE THE STEPS PLEASE?
AYes, you can. If it’s large, you may need an excavator to get out the root ball. If moving it to a pot or crate, make sure it’s at least 1m in size. First of all, prepare the ground or pot. Enrich the garden bed with compost and aged cow manure, and ensure the new spot is well drained, or use premium-quality potting mix. On moving day, trim the canopy and tidy up broken or snapped roots.
Lift the tree from its old hole onto builder’s plastic or hessian strapping, and slide it to its new position. Do not pull or hold the tree by the trunk. Use the hessian or plastic as a sling to manoeuvre the tree into place. Water it in, and give the soil a dose of liquid seaweed to reduce transplant shock. Autumn to late winter is the preferred time, although sometimes you just have to do it out of season. Josh Byrne re-pots a patio lime in our upcoming June issue. Elizabeth
I HAVE TWO VERY LARGE NATIVE TREES (AT LEAST 20 YEARS OLD) IN MY GARDEN THAT WERE PLANTED IN A BRICK-WALLED RAISED GARDEN BED. THEY TOWER OVER THE HOUSE, AND TOUCH THE FRONT GUTTERING. SHOULD I GO FOR A SIMPLE TRIM BACK FROM THE GUTTERING OR DO THEY ALSO NEED TO BE TRIMMED ACROSS THEIR TOPS? Sue, Woodbine, NSW
AThe decision may well depend on what species they are and how they respond to pruning. Personally,
I’m never comfortable with trees that tower over houses. They may be fine day to day, but it only takes one freak weather event to cause some damage. Without knowing or seeing the trees, the best advice I can give you is to engage an arborist – a tree-care professional – to assess the trees and advise you on how best to manage them. Phil
CAN YOU TELL ME WHAT IS EATING MY ROSE LEAVES? PERFECT CIRCLES ARE CUT OUT OF THE LEAVES, STARTING FROM THE EDGES.
AAin’t nature grand! Leafcutter bees clip perfect round or oval sections of leaves to line their nests. Preferring soft, new growth of plants such as roses, wisteria, Robinia spp. and Buddleja spp., the female bee snips a neat, uniform section of leaf with her jaws, and then delicately curls it under her body, securing it with her legs. She then takes flight, off to build her cylindrical nest in a narrow cavity. Even more remarkable is that she makes individual compartments, each containing bee larvae and food, then seals them and repeats the process along the cylindrical nest. Try capturing her leaf-cutting prowess on your phone or other camera. Elizabeth
SINCE MOVING HOUSE, WE HAVE HAD AN ONGOING PROBLEM FOR OVER A YEAR WITH OUR INHERITED CAMELLIA HEDGE, WHICH MUST BE AT LEAST 20 YEARS OLD. THE BRANCHES HAVE BEEN DYING BACK, STARTING AT THE TIPS, AND WE’VE LOST THREE BUSHES. WE HAVE TRIED WHITE CURL GRUB KILLER, COW MANURE, COMPOST, BLOOD AND BONE AND LIQUID SEAWEED. ANY SUGGESTIONS? Elizabeth and Gary, Glenhaven, NSW
AHave you been doing any concreting nearby? Sometimes, people render a wall or do some other kind of cement work around their garden, then they wash out the wheelbarrow near the tap, which affects any plants that are growing nearby. Camellias don’t like lime, and this is my guess for what’s affected your hedge. The same thing can happen when you put a plant in a new cement pot. Lime can leach out of the cement for quite some time, affecting plants that prefer growing in a more acidic environment. Sophie
MY ‘LITTLE GEM’ MAGNOLIA, WHICH IS IN SEMI-SHADE, IS SPINDLY AND SLOW-GROWING. WOULD A BIG PRUNE AND FEED HELP?
AYes! Enrich the soil with organic matter, such as compost and cow manure. Spread it on as a mulch, about 5cm thick. Also, apply a controlled-release fertiliser in spring and autumn around the drip line. Increase the watering – give the plant a good, deep soaking once a week. If you want a dense, compact shape, prune the plant regularly, especially after flowering, but ease off pruning once the new flower buds appear. Elizabeth
SPANISH MOSS IS INVADING OUR TREE CANOPIES. IT IS BEHAVING LIKE A WEED IN MY AREA ON SYDNEY’S NORTH SHORE. IS THE HORTICULTURAL INDUSTRY REVIEWING ITS INVASION OR REMOVING THE PLANT FROM SALE? NOTHING CAN GET RID OF IT, AS IT IS UP IN THE TREE CANOPIES.
ASpanish moss ( Tillandsia usneoides), also known as old man’s beard, is a tree-dwelling bromeliad that’s often associated with the Florida Everglades. It can become a weed in Australia in warmer areas with high humidity, and is on the New South Wales Department of Primary Industries weed list. In such areas, it is best grown as an indoor plant or in a shadehouse that is protected from birds (they use it as nest material). Selective pruning of trees may increase sunlight and air movement, which can help reduce its spread. Judy
DO COFFEE GROUNDS HELP VEGETABLES GROW IF FRESHLY SPRINKLED AROUND? HOW MUCH CAN I USE AND HOW OFTEN? Chris, Morisset, NSW
AIdeally, add the grounds to the compost bin or worm farm, and let them break down. If you don’t have compost or worms, sprinklethem around different parts of the garden each time. Elizabeth
I HAVE A BUNYA PINE, PLANTED FROM SEED, THAT’S GROWING IN A BONSAI POT. IT’S ABOUT 30CM HIGH, HEALTHY AND IS NEVER PRUNED. HOW LONG WILL I BE ABLE TO KEEP IT IN THE POT? Cynthia, Canberra, ACT
AThe art of bonsai, where you create the illusion of a fully grown tree in miniature, is centuries old. A bonsai that’s well cared for will last for decades. Keeping it in a small bonsai pot will restrict the root growth, and trimming the foliage keeps the leaves smaller, too. To maintain the bonsai, remove the tree from its pot every two to four years during late winter, tease out and trim off about a third of the roots, then re-pot into the same container using potting or bonsai mix.
Bonsai require very well-drained potting mix and careful, regular watering to keep the roots moist. The best position for these plants is in a sheltered spot outdoors, although they can be brought indoors for a day or two for temporary display.
Bunya pine ( Araucaria bidwillii) is a huge tree in its natural habitat and, given space, it can reach 35m tall and has a lifespan of up to 600 years. The National Arboretum in Canberra has an impressive bonsai collection – its oldest plant is 60 years old. It’s worth a visit there to pick up some growing and care tips. The Association of Australian Bonsai Clubs is another source. Visit aabcltd.org. Elizabeth
I’M FINDING LOTS OF NEMATODES IN MY ABOVE-GROUND GARDEN BEDS. WHAT’S THE BEST WAY TO MANAGE THEM? Helen, Caringbah South, NSW
AIf you are growing food in your raised beds, steer away from chemical controls, as these aren’t safe to use with edible plants. The traditional organic solution for nematodes is molasses. There is a recipe supplied by Jerry Coleby-Williams on the Gardening Australia website (abc.net.au/gardening) that is worth trying.
It is essentially as follows:
Mix 8L warm water with ½ cup blackstrap molasses and 1L full fat organic cow’s milk. This makes enough for a 9L watering can. Water weekly over plants and soil until plants recover.
This treatment works by encouraging microbial action in the soil. Other things that you can do are practise crop rotation, which helps prevent a build-up of problems, and increase the organic content of your soil by regularly forking in some worm castings or organic-based, pelletised poultry manure or compost, either homemade or bought. Sophie