No-dig or tilling: which is right for your garden?

For a long time, a good gardener was someone who turned their beds over every season. These days many gardeners barely dig at all. Both camps grow good food. The question is what suits your soil, your time and your back.

What digging does

Turning soil over has real effects, some helpful and some not.

The upside:

• It loosens hard, compacted ground quickly.
• It lets you mix in compost, manure or gypsum through the root zone.
• It buries weeds and the remains of old crops.
• Loose soil makes it easy to plant and to sow root crops.

The downside:

• Structure breaks down. Healthy soil is full of crumbs held together by roots, fungi and the sticky by-products of soil life. Digging breaks these crumbs up. In the short term the soil looks fluffy, but over time it can slump and form a crust after rain or watering.
• Fungi get cut up. Many plants partner with fungi whose fine threads reach far into the soil and bring back water and nutrients. Those networks take time to rebuild after each dig.
• Earthworms are disturbed. Worms build long burrows that carry air and water down. Digging destroys those burrows and exposes worms to birds and drying out.
• Organic matter burns off faster. Mixing air into the soil speeds up how fast organic matter breaks down, so you need to keep adding more.
• Weed seeds come up. Most soils hold a bank of dormant weed seeds. Every dig brings a fresh batch to the surface where they can germinate.

What no-dig does

In a no-dig garden you add organic matter to the surface and let worms and soil life take it down. You plant through the top layer and leave roots in place when crops finish, cutting plants off at ground level instead of pulling them.

Gardeners who switch often notice:

• Fewer weeds after the first season or two.
• Soil that stays moist longer under mulch, which matters in a dry climate.
• More worms.
• Less work and less strain on the back.

It's not magic, though. No-dig beds need a steady supply of compost and mulch, and slugs and snails can enjoy the cover. Very compacted or poorly drained ground may need help first.

When digging is still useful

A balanced approach is to dig when there's a real reason, then stop.

• Breaking up compacted ground, once. Old lawns, paths and ground driven on by builders can be packed hard. A single deep loosening with a garden fork, broadfork or spade gets roots and water in. After that, protect the soil so it doesn't compact again.
• Starting a new bed on heavy clay. Many Adelaide plains suburbs have heavy clay. For a new bed, forking in gypsum and plenty of compost helps the clay form crumbs and drain better. Do it once, when the soil is moist but not wet, and then switch to adding material on top.
• Getting rid of tough perennial weeds. Couch and kikuyu runners may need digging out, or smothering for a long time.
• Harvesting root crops. Potatoes, carrots and sweet potatoes have to come out somehow. Fork gently and spread the soil back as you go.

The key rule for clay: never dig it wet. It smears and sets hard. Squeeze a handful first. If it holds a sticky ball, wait.

How to start a no-dig bed

You can start one on lawn, weedy ground or an existing bed. Late winter and autumn are good times, so the layers have a few weeks to settle before planting.

1. Cut down what's there. Mow or slash weeds and grass low. Leave the roots in place.
2. Water the ground well.
3. Lay cardboard. Use plain brown cardboard with tape and labels removed. Overlap the sheets by 15 to 20 cm so weeds can't sneak through the gaps. Wet it thoroughly.
4. Add compost. Spread a good layer of compost or a compost and soil mix on top, around 10 to 15 cm. This is where you'll plant.
5. Mulch. Finish with a few centimetres of pea straw, lucerne or sugar cane mulch.
6. Water again and let it settle.

You can plant seedlings straight away by pulling back the mulch, making a hole in the compost and, if needed, poking through the cardboard. Leafy crops like lettuce and silverbeet are easy first plantings. Carrots and other root crops do better once the cardboard has broken down and the layers have mixed, usually after a season.

Very persistent weeds like couch may push through. Pull them as they appear, and add another layer of cardboard over bad patches.

Keeping it going

• Add a few centimetres of compost to the surface once or twice a year.
• Keep the soil covered with mulch or plants at all times.
• Cut finished crops at the base and leave the roots to rot in place.
• Use paths, stepping stones or narrow beds so you never stand on the growing area.
• Grow green manure or broad beans over winter in beds you're resting.

So which should you choose?

If your soil is already reasonable, no-dig will usually make it better with less work. If it's badly compacted or heavy clay, a single thorough preparation followed by no-dig gives you the best of both. Plenty of gardeners land somewhere in the middle, and that's fine. The goals are the same either way: lots of organic matter, soil kept covered, and as little compaction as you can manage.

In Patchmates

Add a note to the beds you've switched to no-dig, and a task to top them up with compost each autumn.