Autumn (fall) overseeding

Why early autumn

Seed germinates fastest in warm soil, and in September the soil is still holding summer heat while the air is cooler and moister. The new grass then has the whole autumn to root before winter, and it does not have to survive a summer heatwave in its first months, which is the weakness of spring overseeding.

Prepare first

Seed needs to reach soil, not sit on thatch. Scarify first, and on compacted ground aerate as well. Mow a little shorter than usual beforehand so light reaches the seedlings.

How to sow

• Use the same seed mix as the existing lawn, at 10–15 g/m² (about 2–3 lb per 1,000 sq ft). Bare patches can take the full new-lawn rate.
• Spread it in two passes at right angles, then rake it in lightly or brush it into the aeration holes.
• A thin top-dressing of fine compost or sandy soil over the seed helps it hold moisture.
• Feed the new seedlings with a starter fertilizer high in phosphorus, not a high-nitrogen or autumn feed.

Keep it moist for three weeks

Most overseeding fails because the surface dries out. Water lightly once or twice a day so the top 1–2 cm stays damp until the new grass is up and growing, then return to normal, less frequent watering.

Do not combine with a pre-emergent

A pre-emergent applied for annual meadow-grass (Poa annua) in late summer also stops your grass seed. Choose one or the other for the same autumn.