Autumn gardening guide

Date posted: 01 March 2018

Can you believe it's March already? In a few weeks' time we should start to see Mount Lofty Botanic Garden's leaves begin to develop their signature tints, but until then it's the perfect time to start getting your garden into shape for the season ahead.

If you’re scratching your head at where to begin, never fear - we asked our horticultural curators and staff at The Diggers Garden Shop for their top autumn tips.

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Plant, plant, plant!

Autumn’s the ideal time of year to plant – particularly trees, shrubs and perennials – because air temperatures have cooled, soil temperatures are still warm and you hope we’ve had some rainfall to increase soil moisture. First consider the state of your soil because this is the time to undertake any soil improvements, such as mixing in soil conditioners, prior to planting.

When the soil’s warm and moist, new plantings will establish good root growth before slowing down in winter. You’ll see benefits again in early spring, when the plant you planted in autumn – which has had time to establish – puts on wonderful new growth ahead of next summer’s heat.

Autumn’s also a good time to begin transplanting any shrubs or trees, and to make new plants from cuttings. Take 10-centimetre cuttings from hardwood herbs such as rosemary and bay or natives such as banksias, grevillea and coastal rosemary. Remove the lower leaves, dip cuttings into hormone powder and pot in small containers of premium potting mix. Keep just moist and shelter from strong wind and sun.

Watch your soil

As mentioned above, you want your soil to be moist, and after a really hot and dry summer, these cooler autumn days and nights are a relief for gardeners and plants alike. But don't let the cooler temperatures lull you into a false sense of security when it comes to watering your garden and potted plants. It can take numerous rainfall events before the water will penetrate deep enough into the soil for the plant roots to uptake. Keep observing your soil moisture levels, even through the cooler and milder days.

Kitchen gardening

Start forward planning and planting now for your winter crops to ensure a bumper harvest! Try to get all brassicas (cabbage, kale, Asian greens, broccoli and cauliflower, etc.) in by the end of March. Our Little Sprouts Kitchen Garden curator finished sowing all the seeds for her autumn crops last week, and they'll stay in our glasshouse to harden off before they go into the ground. She intends to sow more seed in late March/early April to keep us going through the winter.

The team at the Diggers Garden Shop are experts on what to plant year-round, and they have the following advice for the season ahead: "If your vegetable patch is looking tired, consider planting a green manure crop to add life to an overworked patch. Excellent choices include fenugreek, bio-mustard and a specialist Autumn Green Manure mix available at Diggers.

There are lots of plants that you can sow in autumn including: cabbage, broccoli, cauliflower, Asian greens, lettuce, rocket, silverbeet and spinach, as well as gorgeous sweet peas and Australian wildflowers. Diggers have 10 different sweet peas to choose from including the most sweetly-centred and fragrant Flora Norton. Its also a great time to plant perennial herbs including rosemary, mint, marjoram, thyme, lemon balm and sage.

It's time to top up the mulch on your veggie patches, herb gardens and ornamental beds, but it's best to do this after watering. It's also time to reward your garden with an organic seaweed fertiliser and rockdust to increase trace minerals.

Diggers Adelaide also have a fully-stocked range of glorious autumn flowering perennials including salvias, sedum, dahlias and lavender; garlic ready to plant; spring flowering bulbs' vegetable and perennial flower seedlings including hollyhocks and foxgloves; indoor plants; quality garden tools and specialist garden books."

Fertiliser

Choose a well-balanced fertiliser – one in which the nitrogen: phosphorus: potassium ratio contains similar percentages plus calcium. This will encourage plant cells to thicken, making your plants more resilient to fungus and disease during the cold and wet of winter.

Lawn care

Autumn’s ideal to help your lawns recover from the hot and dry summer, and to prepare them for the wetter and colder months. It’s a good time to fertilise your lawn, but ideally you want a lower nitrogen content fertiliser than what you use in spring and summer. A more even balanced NPK (nitrogen, phosphorus and potassium) fertiliser will help repair damaged areas by promoting new growth, but will also importantly promote new root growth before soil temperatures drop, giving your lawn a head-start for next spring. Remove fallen leaves from your lawn regularly as these will deprive the lawn of light, causing die back and brown patches.

On the rose

For rose aficionados, autumn’s the time to fertilise to ensure your roses have a good supply for that final specky autumn flush. Neutrog’s Sudden Impact for Roses is a perfect choice.

Worms

Earthworms are a sign your soil is fertile. When you add organic matter such as leaves and cow manure to your garden soil, you'll attract earthworms, so there's no need to add more to your garden. The worms you’ve attracted with organic matter will add nutrients from their castings, and make tunnels. Check for borer damage on all deciduous trees, paying attention to the trunk at soil level. It‘s easier to check when trees are dormant and bare.

Leaf matters

This time of year produce a lot of leaf matter and you can use this to start a compost of leaves (such as Oak in particular). Traditionally “Oak leaf mould” was an integral part of potting mixes, but more recently it has been replaced by peat-moss (coir or natural) and pulverised composted Pine bark.

Other handy hints

Good garden hygiene at this time is a great idea. Take care around the base of shrubs and trees to limit the build-up of mulch and matter around the stem/trunk region, particularly in high rainfall areas such as the Adelaide Hills. This helps prevent collar rot and other fungal attack.

Pruning of some species of tree, for shape more than anything, also is a good idea. Some trees, Maples in particular, will bleed if you leave it too late. Pruning too early or too late can open also open the tree to fungal attack through the wound.

This season there will be a lot more of the down and powdery mildews, particularly in the Adelaide Hills. The soft option is spraying with milk, but there are also preparatory fungicides available too (just make sure to read the instructions well).

Trim hedges before the onset of winter to keep them compact and bushy from ground level.