Mulching 101: Why It Matters More on the Coast
If you only do one thing in your garden each year, make it mulching. On the Mornington Peninsula, mulch isn’t a nice-to-have — it’s essential. Our sandy soil heats up fast, dries out fast, and loses nutrients fast. A proper mulch layer fixes all three problems.
What Mulch Does
Think of mulch as a blanket for your soil. In summer, it keeps soil temperatures down by as much as 10 degrees. In winter, it insulates roots from cold. Year-round, it holds moisture in, suppresses weeds, and slowly breaks down to feed the soil.
On sandy coastal soil, mulch is even more important because there’s less organic matter to hold things together. Without mulch, water runs straight through and nutrients wash out with every rain.
Choosing the Right Mulch
Not all mulch is created equal. For Peninsula gardens:
Best options:
- Coarse bark chips — long-lasting, looks tidy, doesn’t blow away in coastal wind.
- Arborist’s wood chip — free or cheap, great for large areas. It’s a mix of bark, wood, and leaf that breaks down into beautiful soil over time.
- Sugar cane mulch — lightweight and breaks down faster, adding organic matter to sandy soil quickly. Needs topping up more often.
Avoid:
- Fine pine bark — compacts, repels water, and blows around in wind.
- Pebbles and gravel — don’t feed the soil, heat up in summer, and weeds grow through them anyway.
- Dyed mulches — the dye can leach chemicals and they’re generally made from poor-quality recycled wood.
How Thick
Seven to 10 centimetres is the sweet spot. Less than five centimetres and weeds push through easily. More than 15 centimetres can prevent rain reaching the soil and create habitat for pests.
Spread mulch evenly across the whole bed, but keep it a hand’s width away from plant stems and trunks. Mulch piled against stems holds moisture against bark, causing collar rot — a common and preventable way to lose plants.
When to Apply
Twice a year is ideal: once in late autumn (after feeding the soil) and once in early spring (after the first round of weeding and feeding). The autumn application protects soil through winter. The spring top-up gets you through summer.
The Water Penetration Test
After mulching, give the area a water and check that moisture is getting through to the soil underneath. Some mulches, particularly if they’ve dried out, can become water-repellent. If water beads up and runs off, break the mulch surface up with a rake and water again slowly.
On the Peninsula, the combination of wind and sandy soil means mulch breaks down faster than in sheltered inland gardens. Budget for topping up more frequently, and view this as a positive — that broken-down mulch is feeding your soil.