Will grass grow at 40 degrees?

Grass growth is dependent on several factors, most importantly soil temperature. Grass typically stops growing when temperatures drop below 50 or 40 degrees Fahrenheit. However, some cool-season grasses can continue growing at colder temperatures. This article will examine how temperature affects grass growth, which grasses grow at 40 degrees, and tips for encouraging grass growth in cool weather.

How Temperature Affects Grass Growth

Temperature affects grass growth by impacting photosynthesis. Photosynthesis is the process grasses use to convert sunlight into energy and nutrients. Warm-season grasses thrive in temperatures between 80-95 degrees Fahrenheit, while cool-season grasses prefer 60-75 degrees. Below 50 degrees, photosynthesis slows down dramatically.

Enzymes needed for growth also work best within an optimal temperature range. For warm-season grass, this is 80-95 degrees. For cool-season grass, it’s 60-75 degrees. When temperatures drop below 50 degrees, enzyme activity declines. This slows nutrient intake, cell division, and ultimately, growth.

Soil temperature specifically impacts root growth and function. Grass roots absorb water and nutrients from the soil to support growth above ground. Cooler soils contain less accessible nutrients and water. Roots also grow slower in cold soil. Weakened roots cannot properly support leaf and blade growth.

Which Grasses Grow at 40 Degrees?

Most warm-season grasses will stop growing when temperatures drop to 40 degrees Fahrenheit or below. However, some cool-season grasses can continue growing at temperatures close to freezing:

Tall Fescue

Tall fescue is a hardy, cool-season perennial lawn grass. It can withstand cold winters, tolerating temperatures as low as 20 degrees Fahrenheit. Growth slows considerably below 50 degrees but doesn’t stop completely until near freezing temperatures. Tall fescue will continue growing, albeit slowly, at 40 degrees.

Perennial Ryegrass

Like tall fescue, perennial ryegrass is a cool-season grass. It thrives in cool, wet climates. Perennial ryegrass can tolerate temperatures down to 20 degrees Fahrenheit. It continues growing at a slow rate when temperatures drop below 50 degrees in fall and winter. Expect some growth at 40 degrees Fahrenheit.

Fine Fescue

Fine fescues like hard fescue, sheep fescue, and creeping red fescue grow well in cold climates. Fine fescues prefer temperatures between 60-75 degrees Fahrenheit but tolerate anything above freezing. At 40 degrees, fine fescues will still actively grow and recover from wear, just at a reduced rate.

Kentucky Bluegrass

Kentucky bluegrass grows best in spring and fall when temperatures are 60-75 degrees Fahrenheit. It tolerates cold better than warm-season grasses. While its growth slows down dramatically below 50 degrees, Kentucky bluegrass can remain active at temperatures above freezing. Expect to see some growth at 40 degrees Fahrenheit.

Bentgrass

Bentgrass varieties like creeping bentgrass and colonial bentgrass thrive in cool weather. Bentgrass tolerates cold temperatures down to 32 degrees Fahrenheit. It will continue growing at 40 degrees, though its growth rate will be reduced. Bentgrass prefers consistent moisture and cool temperatures.

Tips for Encouraging Grass Growth at 40 Degrees

While grass growth slows considerably at 40 degrees Fahrenheit, proper care can encourage faster growth:

  • Mow infrequently – Mowing puts extra stress on grass. Limit mowing to 1-2 times per month in cold weather.
  • Raise mower height – Keep grass 2-3 inches tall to allow more leaf surface area to absorb sunlight.
  • Leave clippings – Clippings decompose and return nutrients to the soil.
  • Aerate soil – Aeration reduces compaction and helps roots grow.
  • Fertilize – Apply a high-nitrogen fertilizer to energize growth.
  • Water thoroughly – Moist soil helps roots absorb nutrients.
  • Reseed bare spots – Repair thin or bare areas to thicken up turf.
  • Control thatch – Too much thatch inhibits water, air, and nutrient circulation.

Avoid nitrogen fertilization after late fall to harden plants off for winter dormancy. Letting grass go dormant over winter is natural and healthy. Continue mowing until growth stops completely.

Effects of Prolonged Temperatures Around 40 Degrees

If temperatures hover right around 40 degrees Fahrenheit for an extended period, cool-season grasses will remain semi-dormant. Growth will be very minimal with limited recovery and repair. Prolonged cool temperatures can lead to:

  • Thinning turf cover as growth stops.
  • Slow green up in spring as grass recovers from prolonged dormancy.
  • Increased disease and pest pressure on stressed plants.
  • Reduced energy reserves after extended minimal growth.
  • More weed competition in bare spots and thin turf.

Stress from consistently cool temperatures of around 40 degrees makes grass more vulnerable to further stresses. For example, traffic on dormant grass can easily damage plants.

Warm-Season Grasses at 40 Degrees

Warm-season grasses like bermudagrass, zoysia, and buffalo grass will enter complete dormancy when temperatures remain around 40 degrees Fahrenheit or lower. Growth stops as the plants shut down. Prolonged cool temps can lead to:

  • Brown, dormant turfgrass.
  • No self-repair of damaged areas.
  • Thin turf cover as warm-season grasses go dormant.
  • Increased vulnerability to disease and pests.
  • Very slow spring green-up and recovery.

Warm-season grasses need over 50 degrees for active growth and will remain dormant with prolonged temperatures of 40 degrees and under. Letting them go brown and dormant is normal, though take care not to overuse dormant turf.

Does Grass Stop Growing Below 40 Degrees?

Most grass species will stop active growth when temperatures remain below 40 degrees Fahrenheit. The exception is some hardy cool-season grasses that can tolerate near-freezing temperatures.

Grass Type Stops Growing Below
Warm-season grasses 50 degrees
Tall fescue 20 degrees
Perennial ryegrass 20 degrees
Fine fescues 32 degrees
Kentucky bluegrass 32 degrees
Bentgrass 32 degrees

So warm-season grasses will stop all growth below 40 degrees Fahrenheit. But cool-season grasses can continue growing, albeit minimally, at temperatures between 30-40 degrees.

Grass Growth Rate at 40 Degrees

At 40 degrees Fahrenheit, grass growth is very minimal, even for cold-tolerant species. Expect growth rates around 10-20% of optimal levels or less. Here are estimated growth rates for different grass types at 40 degrees:

Grass Type Growth Rate at 40°F Optimal Growth Rate
Warm-season grasses None 2-3 inches / week
Tall fescue 0.1-0.25 inch / week 1-2 inches / week
Perennial ryegrass 0.1-0.25 inch / week 1-2 inches / week
Fine fescues 0.1-0.25 inch / week 0.5-1 inch / week
Kentucky bluegrass 0.1-0.25 inch / week 0.5-1.5 inches / week
Bentgrass 0.1-0.25 inch / week 0.5-1 inch / week

These are rough estimates, but indicate how minimal grass growth is at 40 degrees Fahrenheit. Growth rates slow to 10-25% of optimal levels or less for cool-season grasses. Warm-season grasses stop completely when temperatures are stuck at or below 40 degrees.

Grass Growth with Fluctuating Cold Temperatures

Grass growth patterns change when temperatures fluctuate above and below 40 degrees Fahrenheit:

  • Warmer daylight temperatures – Can stimulate growth despite overnight freezes.
  • Consistent cold temperatures – Promote full dormancy and temporary shutdown of growth.
  • Alternating cold and warm – Leads to stunted, inconsistent growth as grass struggles to adapt.
  • Hard frosts – Can damage turf and set back growth as plants repair freeze injury.
  • Gradual temperature drops – Allow grass to harden off properly for dormancy.

The ideal condition for cool-season grasses is consistent cool temperatures between 50-60 degrees Fahrenheit. Erratic fluctuations above and below 40 degrees lead to stressed, inconsistent growth.

Effects of Freezing Temperatures on Grass

Freezing temperatures can damage and even kill grass plants:

  • Ice crystal formation ruptures cell membranes.
  • Desiccation as water moves out of cells.
  • Wilting and browning as plants lose rigidity.
  • Death of crown and roots from severe freeze injury.

Actively growing grass is most vulnerable to frost and freeze damage. Dormant grass can survive very cold temperatures with less risk of injury. Other factors impacting freeze tolerance include:

  • Grass species – Warm-season less tolerant than cool-season.
  • Health and vigor – Weak plants more vulnerable.
  • Soil moisture – Drier soils more prone to freeze.
  • Duration of cold – Longer freezes cause more damage.
  • Low mowing – Freezes injure shorter grass easier.
  • Residue cover – Insulates plants against freezing.

Heavily used turf areas like sports fields are also more prone to freeze injury from reduced crown cold tolerance.

Tips for Growing Grass in Cold Weather

Encouraging grass growth when temperatures drop below 50 degrees Fahrenheit requires proper care:

  • Select cold hardy grass varieties – Such as tall fescue, fine fescue, perennial ryegrass, and Kentucky bluegrass.
  • Mow infrequently – Remove no more than 1/3 of grass blade length when mowing dormant turf.
  • Leave grass clippings – Provides insulation for grass plants and crowns.
  • Fertilize in fall – Applies nutrients for winter hardening and root growth.
  • Improve drainage – Allows soil to dry and warm up faster after freezes.
  • Aerate compacted areas – Reduces puddling and surface frost.
  • Reseed bare spots in fall – Gives new grass a chance to establish before winter.
  • Control thatch – Thatch retains excessive moisture that can freeze.

When temperatures drop below 40 degrees, switch to winter lawn care practices to help grass survive cold weather. Resume normal care when consistent spring temperatures arrive.

Transitioning Warm-Season Grass to Dormancy

As warm-season grasses like bermudagrass and zoysia go dormant in winter, proper fall care ensures health in spring:

  • Reduce irrigation – Slowly let turf dry out as growth stops.
  • Lower mowing height – Gradual reduction avoids shock.
  • Apply winterizing fertilizer – High potassium formula aids dormancy.
  • Reduce traffic – Prevents dormant turf damage that’s slow to repair.
  • Control pests and weeds – Treat existing issues before dormancy.
  • Top dress thin areas – Covers and insulates dormant grass.
  • Overseed if needed – Ryegrass provides green cover.

Let warm-season turf go fully dormant and brown in winter. Avoid high traffic while dormant and irrigate only if prolonged drought occurs.

Conclusion

At 40 degrees Fahrenheit, most grass growth slows to a crawl or stops completely. Warm-season grasses will go dormant and stop growing when temperatures remain around 40 degrees or below. Cool-season grasses tolerate colder temperatures but still only grow minimally at 40 degrees, at about 10-25% of their peak growth rate. While grass can survive extended 40 degree temperatures, growth is very limited. Fluctuating cold temperatures create stress and inconsistent growth. Proper winter lawn care and preparation in fall helps minimize damage and encourages faster spring green-up. Adjusting practices based on seasonal temperatures ensures a healthy, thriving lawn all year long.

Leave a Comment