Garden Bark & Mulch

A depth of 5–10cm is the recommended range for most NZ garden applications. Apply 5–7cm around vegetable beds and smaller plants, and 7–10cm around shrubs, trees, and larger ornamental beds where longer-lasting weed suppression is needed. Too shallow and weeds will push through; too deep and water may struggle to penetrate to the roots below. Keep mulch away from the base of plant stems and tree trunks — leave a 5–10cm gap to prevent rot.

In most NZ gardens, mulch should be replenished once or twice a year — typically in spring before the growing season begins, and again in late summer or early autumn before winter. Bark mulch breaks down slowly and may only need topping up once annually. Finer organic mulches like pea straw break down faster (usually within one growing season) and need replenishing every spring. Rather than doing a full replacement, top up to restore your desired depth — usually adding 3–5cm is enough to refresh the look and effectiveness.

The terms are often used interchangeably, but there are differences. Bark mulch is specifically made from shredded or chipped tree bark — it’s longer-lasting, slower to decompose, and ideal for ornamental beds, paths, and around trees and shrubs. Garden mulch is a broader term that can include a range of organic materials: bark, pea straw, wood chips or compost. At Gammans, all bark and mulch products are manufactured on-site at our Omokoroa yard, meaning consistent quality and reliable supply — unlike suppliers who source from external stock.

Yes — mulch is one of the most effective chemical-free weed suppressants available. A layer of 5–7cm depth blocks most weed seeds from receiving the light they need to germinate. It won’t eliminate weeds entirely (some persistent weeds will still push through), but it dramatically reduces the weeding workload through the growing season. For best results, remove existing weeds before mulching, and maintain the correct depth. Coarser bark grades like #5 Bark Nuggets tend to outperform finer mulches for long-term weed suppression.

For vegetable gardens, pea straw is widely regarded as the best mulch in NZ. It’s soft enough to plant through, breaks down to add nitrogen and organic matter to the soil, retains moisture around plant roots, and is particularly effective for tomatoes, courgettes, and strawberry beds. Fine bark mulch (like Gammans #3 Decorative Mulch) also works well around vegetable beds for moisture retention and weed suppression and as a pot topper. Many experienced gardeners use pea straw in the veggie patch and bark mulch in ornamental areas — the best of both worlds.

No — when applied correctly, bark mulch is beneficial for plants. The key is correct application depth (5–10cm) and keeping mulch away from plant stems and tree trunks. For new plantings it’s worth adding a slow-release fertiliser below the mulch layer when you apply it.

Calculate: Length (m) × Width (m) × Depth (m) = Volume in cubic metres (m³). For example, a 4m × 5m garden bed mulched to 7cm depth requires 4 × 5 × 0.07 = 1.4m³. One cubic metre covers roughly 10–20m² depending on depth and the grade of mulch. If you’re buying in bags, most bulk bags contain 0.6–1m³. If you’re unsure about your quantities, drop into the Gammans yard with your measurements — or call us on 027 548 1278. We work through these calculations with customers every day.