Grow It Green: How to Ready Your Lawn for Fall

When the heat of July finally starts to fade, many of us wonder whether we should keep mowing, watering, or just let the lawn take a break. The answer, according to Kendall Kunelius of UNH Cooperative Extension, is a careful balance of maintenance and a few strategic pauses.

First off, check your mower deck. September is the perfect time to raise the cutting height to about 3‑inches. A slightly taller blade lets the grass store more energy, which it will need to survive the chilly nights ahead. Don’t be tempted to cut it super short; that only stresses the roots.

Watering also changes its rhythm. As temperatures dip, the grass doesn’t need daily sprinkling. Aim for about an inch of water per week, delivered in one or two deep soakings rather than a light daily spray. Deep watering encourages roots to grow downwards, making the lawn more drought‑resilient for the winter.

One of the biggest “gotchas” in late summer is that‑by‑now the soil is often compacted from spring traffic and summer footfall. If you can, rent a core aerator or ask a local garden center about a walk‑behind version. Pulling those small plugs out creates air pathways, letting water and nutrients reach the grassroots more easily.

After aerating, consider overseeding. Cool‑season grasses—fescues, ryegrass, and the classic New England bluegrass—still germinate well in September. Spread a thin layer of seed, then lightly rake it in and keep the area moist. Within a few weeks you’ll see a denser, greener carpet that’ll hold up better against the first frosts.

Fertilizer timing matters, too. A light, slow‑release nitrogen application now will feed the grass through the fall, but avoid high‑phosphorus blends that can leach into waterways. The extension office often recommends a 3‑1‑2 N‑P‑K ratio for New Hampshire lawns in September.

Leaves—those beautiful autumn confetti—are a double‑edged sword. A thin blanket can protect the grass from wind‑burn, but a thick mat blocks light and traps moisture, inviting disease. Sweep or rake regularly, especially after heavy falls, and compost the pile rather than letting it sit on the lawn.

Finally, keep an eye on weeds. The heat of summer may have encouraged crabgrass or dandelions to set seed. A post‑emergent herbicide applied now, following label directions, can curb their spread before winter sets in.

In short, September is a busy but rewarding month for lawn lovers in New Hampshire. Aerate, overseed, adjust mowing height, water wisely, and give weeds a gentle nudge. Follow these steps, and you’ll walk out onto a carpet that looks just as good in October as it did in July.