Kentucky bluegrass
Poa pratensis
Known for its deep blue-green colour and for creeping rhizomes that let it repair its own damage. Very cold-hardy, but unhappy in hot humid summers — in Japan it suits cooler regions.
At a glance
| Family | Poaceae |
|---|---|
| Season type | Cool-season |
| Heat tolerance | ●●●●● |
| Cold tolerance | ●●●●● |
| Shade tolerance | ●●●●● |
| Wear tolerance | ●●●●● |
| Drought tolerance | ●●●●● |
| Mowing height | 25–60 mm |
| Propagation | Seed / Sod |
| Upkeep | Medium upkeep |
| Native range | Europe, Asia, North Africa |
Growing conditions
| USDA hardiness zones | 2–7 |
|---|---|
| Sunlight | Full sun |
| Watering | High |
| Growth rate | Moderate |
| Soil pH | 6–7.5 |
| Common problems | Rust / Dollar spot / Snow mould / White grubs / Brown patch |
How to grow it
Climate and sun
The most cold-hardy of the common cool-season grasses, at home in northern and upland regions. It creeps by rhizomes, so damaged areas fill in on their own. Where summers are hot, surviving August is the whole game — a spot with afternoon shade often keeps it better than open sun.
Planting
Seed or sod. Seed takes two to three weeks to germinate, so clear weeds thoroughly beforehand or they win the race. Early autumn is the window. It is usually sown in a mix with faster-establishing perennial ryegrass rather than alone.
Watering
It drinks in summer: deep morning water two or three times a week. Little-and-often watering keeps roots shallow and makes the summer worse.
Mowing
Cut at 30–50 mm, weekly in growth. Raise the height in summer so the canopy shades the soil and the plants spend less.
Feeding
Nitrogen-led feeds in spring and autumn. Skip midsummer feeding, which invites disease. Of the year's feeds, the autumn one does the most good.
Problems and winter
Rust, dollar spot, snow mould and root-feeding white grubs. Cold is not a problem — it overwinters under snow. The two months after the rainy season decide the outcome.