How High to Mow a Lawn in Northwest Territories

The mowing height for a lawn in the Northwest Territories depends on the grass: 3 to 3.5 inches for tall fescue, 2 to 3 inches for Kentucky bluegrass and fine fescues, and 1.5 to 2.5 inches for perennial ryegrass and rough bluegrass. Most mixed lawns do well at 3 inches. The growing season is short, so every blade you leave standing is working for the roots, and the table below shows where each species sits.

The mowing height for Northwest Territories lawns

Five cool-season species make up the realistic list here, and their heights are not interchangeable. A lawn of tall fescue cut at 1.5 inches is scalped. A perennial ryegrass lawn left at 3.5 inches flops over and mats. Each figure below sits within the range that land-grant extension services publish for the species.

Why the short season favors the taller end

Grass feeds its roots through its leaves. When the frost-free stretch is a little under four months (the mean dates, covered in the last section, fall on May 25 and September 18), there is little time to rebuild a root system that was clipped back too hard. Taller blades also shade the soil, which slows weed seed germination and keeps the surface from drying out as fast.

If you are not sure what is in your lawn, start at 3 inches. That height falls inside the range for tall fescue, Kentucky bluegrass and fine fescues. It sits just above the range for perennial ryegrass and rough bluegrass, so a ryegrass-heavy lawn can drop to 2.5 inches. The general rules for any lawn are in our guide to Mowing a Lawn.

Why warm-season grasses are off the list

Warm-season grasses such as bermudagrass and zoysia grow when soil is hot and stall in cool weather. Here they would spend most of the year dormant and brown, and they would not reliably survive the winter. Only the five cool-season species above belong in a territorial lawn. Farther north the same logic applies even more strictly, as in How High to Mow a Lawn in Nunavut.

Raising the deck when the heat comes

Summer in Yellowknife is not dry in the way people expect of a northern place, but it is not wet either. The Canadian Climate Normals for the Yellowknife A station (1981-2010) show about 109 mm (4.3 inches) of rain across June, July and August, out of 290 mm (11.4 inches) for the whole year. June is the driest of the three at 29 mm (1.14 inches), followed by August at 39 mm (1.55 inches) and July at 41 mm (1.61 inches).

Those normals are for one station, and they cover 1981-2010. The US figures elsewhere on this site use 1991-2020, so do not line the two sets up as if they were the same yardstick. They tell you what a typical summer looks like, not what this one will do.

Rain never works alone. On sandy soil, an inch of rain drains through within the day, so a lawn on sand can need watering every second day even in a wet summer. Clay holds the same water for a week. And rain that comes as one heavy thunderstorm tends to run off a baked surface instead of soaking in. A hot spell speeds evaporation, and that is when a low cut hurts most, because short grass leaves the soil exposed to the sun.

The practical move is simple. When the heat arrives, raise the deck to the top of your species range: 3.5 inches for tall fescue, 3 inches for Kentucky bluegrass and fine fescues, 2.5 inches for perennial ryegrass and rough bluegrass. Taller grass shades its own roots, and the soil under it stays cooler and holds moisture longer. A hotter, drier place does the same thing at a larger scale, as in How High to Mow a Lawn in Colorado.

A rain gauge on your own plot settles what the station averages cannot. A slope, a rain shadow or a town lot can shift the numbers noticeably. Set a straight-sided can on the lawn and check it after each storm. If a week brings less than an inch in total, the lawn needs a deep watering, not a light daily sprinkle.

The one-third rule, and why it is not arbitrary

Never remove more than a third of the blade in a single cut. Extension services repeat this rule so often that it sounds like folklore, but it reflects how grass works. Each cut removes leaf surface, which is the only part that makes food. Take too much and the plant draws on stored reserves, and the roots stop growing until the leaves catch up.

The arithmetic is easy to apply. Tall fescue held at 3.5 inches should be mowed when it reaches about 5.25 inches, which removes roughly 1.75 inches. Kentucky bluegrass at 3 inches gets cut at 4.5 inches. Perennial ryegrass kept at 2 inches gets cut at 3 inches. Work the rule backward from your chosen height, and the height tells you when to mow.

The rule makes more sense in a short season than almost anywhere. Growth comes in bursts after a wet spell or a warm week, and a lawn can jump from tidy to shaggy while you are away for a weekend. When that happens, resist the urge to cut it back to normal in one pass. Mow to a third off, wait a few days, then mow again. Two gentle cuts do far less damage than one hard one.

Clippings help too. Short pieces drop between the blades and break down, returning some nutrients to the soil. Long, heavy clumps from an overgrown lawn smother the grass underneath, so if you skipped a week, rake them up. If you end up needing to rake clippings regularly, that is a sign you are mowing too infrequently.

The first and last cut of the year

On average, the last spring frost at Yellowknife A falls on May 25, and the first fall frost on September 18. Both are mean dates from Environment and Climate Change Canada. In one year out of two, the frost comes later than the average date, so each date marks the middle of a window rather than a safe line. The normals also cover 1981-2010, and they describe one station. Districts farther north or at higher elevations typically run weeks behind it.

For the first cut, ignore the calendar and watch the grass. Mow when the lawn is clearly growing and the ground is firm enough not to rut under the mower. Soggy, freshly thawed turf tears under the wheels, and early blades give little to cut anyway. Keep the deck at your normal species height, not lower. Scalping a lawn in spring to tidy winter damage removes the very leaf area it needs to wake up.

For the last cut, drop to the lower end of the range, not below it. That means 3 inches for tall fescue, 2 inches for Kentucky bluegrass and fine fescues, and 1.5 inches for perennial ryegrass and rough bluegrass. Long grass that goes under snow can mat down and invite snow mold. Keep mowing as long as the grass is growing, and treat the frost date as a cue to check the lawn, not as a deadline.

For questions about soil, local conditions or what grows in your community, the Northwest Territories Industry, Tourism and Investment agriculture services are the official source. No further local frost data is published here beyond the Yellowknife A normals.

Common questions

Can I grow bermudagrass or zoysia in the Northwest Territories?

No. They are warm-season grasses that need sustained heat to grow and they do not reliably survive long, cold winters. Choose from tall fescue, fine fescues, Kentucky bluegrass, perennial ryegrass or rough bluegrass.

What height works if my lawn is a mix of species?

Pick the overlap. A mix of Kentucky bluegrass and perennial ryegrass can be held at 2 to 2.5 inches, and one with tall fescue and Kentucky bluegrass fits at 3 inches. Start at 3 inches if you cannot tell what is growing.

Do I need to water if Yellowknife gets 4.3 inches of summer rain?

The normal is 109 mm (4.3 inches) across the three months, which is a typical total, not a promise. Sandy soil may need watering every few days even in a rainy stretch. A rain gauge in your own lawn is the better guide.

Do the Yellowknife frost dates apply to my town?

Only roughly. The May 25 and September 18 means come from the Yellowknife A station, and places farther north or higher up usually run weeks behind it. Use them as a starting point and adjust to what your own grass is doing.