How to Calculate Grass Seed & Fertiliser Quantities
Sowing too thinly leaves soil vulnerable to weeds and erosion, while sowing too densely causes seedlings to compete for nitrogen, moisture, and root space. Getting the rate right matters more than most people expect.
Sowing Rates for Warm vs. Cool Season Grasses
- Warm Season (Couch, Kikuyu): Spread via runners once established, so overall sowing density can be lower than cool season grasses — though the exact rate varies hugely between pure single-species seed and retail blends. Always check your specific product.
- Cool Season (Tall Fescue, Ryegrass, Bluegrass): Grows upright in clumps without spreading via runners, so it generally needs a denser sowing rate for full coverage, commonly cited around 40–50g/m² for new lawns.
Oversowing
Repairing bare patches or thickening an existing lawn typically uses roughly half the new-lawn sowing rate, paired with a phosphorus-heavy starter fertiliser to encourage strong initial root growth before the blades take off.
Frequently Asked Questions
Not directly — genuine Australian Buffalo turf (like Sir Walter) isn't sold as seed and has to be laid as turf. "Buffalo grass seed" sold online is a different species and won't match an existing Buffalo lawn. Kikuyu is the closest commonly-seeded alternative if you want a similar broad-leaf, spreading lawn from seed.
Pure single-species seed, especially Kikuyu, is sown very sparingly because each plant spreads aggressively via runners once established. Retail blends that include a fast-germinating "nurse" grass like annual ryegrass (to protect and stabilise the soil while the main species establishes) need a much higher rate, since the ryegrass component behaves like a normal, non-spreading grass. Always use the rate printed on your specific product.
Starter fertiliser is formulated with a higher phosphorus ratio specifically to encourage strong root development in new seedlings, which regular lawn fertiliser (usually nitrogen-heavy, for established green-up) doesn't prioritise in the same way.
Warm season grasses establish best in late spring through summer when soil temperatures are consistently warm. Cool season grasses do best sown in autumn or early spring, avoiding the peak heat of summer which can stress new seedlings.