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Getting the lawn ready for winter

In the Garden

I’ve had a number of calls in the office about preparing a lawn for winter. There are four consideration when dealing with lawns, regardless of the season:

  • Mowing
  • Irrigation
  • Fertilization
  • Weed control
  • Other—on occasion, we also need to worry about compaction and thatch

Some of the recommendations will change as we go into the fall season.


Throughout the summer we continually preach that lawns should be cut high. The longer the leaf blade, the deeper the roots. For Kentucky bluegrass the best height is 2.5 – 3.5 inches. This one practice will save on your water bill and reduce weed pressure for your lawn. Continue to mow high, until the final mowing.

The final mowing should take place after the grass has stopped growing—probably mid-October to mid-November in most of eastern Idaho. Each year is different, and Ashton is different from Pocatello. This last mowing should be short — 2 to 2.5 inches long. This final mowing (which may also have a lot of tree leaves), should be bagged.


Proper fall irrigation will save a lot on your water bill. Water the same amount, just increase the number of days between watering. You shouldn’t be watering more than once a week right now. With cold temperatures, timing becomes an issue. The final irrigation should be about the time of the final mowing (before the ground freezes so your sprinkler system can be winterized) so there is enough soil moisture to make it through the winter.


The final fertilization is probably the most important for lawn health and spring green-up. This final fertilization should be one-half pound nitrogen per 1,000 square feet, and applied just before the final irrigation. Too much fall fertilizer will encourage some winter diseases.

Weed control

Winter annuals are just young seedlings right now and they are easier to control at this young stage. Biennial and perennial weeds, such as musk thistle, bull thistle, dandelion, Canada thistle or field bindweed (morning glory) are moving nutrients down to the roots as the days get shorter and colder. Fall is a good time to get systemic herbicides down to perennial roots. Fall weed control will also reduce the number of early spring weeds.


If you have compaction or thatch problems in your lawn, you may want to aerate this fall.

Compaction occurs in high traffic areas. This keeps oxygen from getting to the roots and they die.

Thatch is the high lignin grass stems that don’t break down very quickly. There can be several reasons for this, but it can mostly be attributed to poor soil health practices.

Core aeration will increase oxygen into the soil, helping to combat both compaction and thatch situations. If you determine that aeration is necessary, be sure to use a core aerator, which leaves the plugs on the soil surface. If all you do is push spikes into the soil, you will actually increase the compaction.

By taking a few steps this fall, you can have an easier spring.

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