Patchy lawn? Find the cause before you buy seed

The standard response to a patchy lawn is a $30 box of "miracle" patch mix from the hardware shop, scattered with hope. Three weeks later: same patches, fatter pigeons. Seed comes last. First, work out why that spot is bare - something made it bare, and it's almost always still there.

Diagnose first

• Patches along the path, the clothesline run, the cricket pitch. Traffic and compaction. The soil's been trodden into concrete and roots can't get air or water into it. If a screwdriver won't push in easily, this is you.
• Thinning under trees or on the south side of the house. Shade. Most lawn grasses want 3-4 hours of direct sun; couch wants more. No seed survives what killed its predecessor.
• Patches that lift like carpet, magpies drilling the lawn. Curl grubs have eaten the roots. Treat the grubs before repairing or you're laying out a second dinner.
• Round spots where the dog goes. Urine burn - see the dead grass guide for the tell-tale green ring.
• Scalped crowns and high spots. The mower's shaving the lawn's high points down to dirt. The fix is cutting height, or levelling the lumps - new grass will just get scalped too.
• General moth-eaten thinning everywhere. Usually hunger plus mowing too short. A lawn cut to the floor every fortnight and never fed will thin out; weeds fill the gaps.

The repair, in order

1. Fix the cause. Aerate the compacted run (a garden fork worked back and forth every 10 cm does a real job on small areas). Treat grubs. Raise the mowing height. Redirect the dog. Accept that deep shade might want pavers or shade-tolerant plants instead of a fifth attempt at grass.
2. Rough up the surface. Scratch the patch back to loose soil with a rake - seed and runners need soil contact, not a thatch mat to sit on.
3. Repair to match your grass. The bit the seed box doesn't mention: if your lawn is couch, kikuyu or buffalo - and in Melbourne's north it usually is - it doesn't grow from the seed in that box anyway. Those lawns repair from runners: feed and water the surrounding lawn and it'll walk back across a small patch in a warm month or two, or cut a strip of turf for instant coverage. Seed is for fescue and rye lawns, sown thick in early autumn or mid-spring.
4. Water like it's a nursery. Light and daily until establishment, which is the one time shallow watering is correct - then taper to deep and infrequent.
5. Keep traffic off. Four to six weeks. Yes, including the dog. Good luck.

When it works

Warm-season repairs take between October and December - the grass has the whole summer to knit in. Fescue goes in around March-April while the soil's still warm but the heat's gone. Mid-winter repairs fail, and February repairs need daily babysitting through the heat. Time it right and a patchy lawn is a one-season fix; keep it fed and mown a notch higher, and the patches don't come back.

Quick answers

Why won't lawn seed fix my bare patches?

Two reasons. Whatever made the spot bare is usually still there, and if your lawn is couch, kikuyu or buffalo it does not grow from the seed in the box anyway. Those lawns repair from runners or a strip of turf; seed is for fescue and rye.

When is the best time to repair a patchy lawn in Melbourne?

October to December for couch, kikuyu and buffalo, so the grass has a whole summer to knit in. March to April for fescue. Mid-winter repairs fail and February repairs need daily watering through the heat.

How do I repair a bare patch in the lawn?

Fix the cause, scratch the patch back to loose soil, repair to match your grass with runners, turf or seed, water lightly every day until it establishes, and keep traffic and the dog off it for four to six weeks.