LAWN: Do you overseed lawns in fall?

If client requests it
Always suggest to client

Update (09/15/2017)

Seed Needs Don't Stop When You Leave

Printable Version [PDF]


Cool September Forecasted to Yield to Early Fall Heat

  1. Early September has mirrored the cool August. - Source: Pat Guinan
  2. This is set to change, however, as the 10-14 d forecast has heat returning. - Source: NOAA

August ended as the coolest since 2004, and the first few weeks of September followed suit. Through September 13th, the month is 3 degrees below normal, but unfortunately forecasts expect that to change over the next two weeks.  High temperatures are expected to climb into the 90s over the weekend, and come slightly back down into the mid to upper 80s through next week. Humidity is also expected to be high, so expect it to be sticky. The good news is that day length is fairly short, so the duration of heat stress on cool season grasses (and us) shouldn’t be as substantial.

A mild cold front is expected to pass through Sunday into Monday and bring the region a much-needed chance of showers. Except for remnants of Irma in southeastern MO, no rain has fallen throughout most of the region since late August. As discussed below non-irrigated turfgrass is entering drought dormancy, and the lack of rainfall is seriously hindering reseeding efforts.

Drought type conditions for most of the region

  1. Over the last 30 days, most areas are 1-2� below normal. - Midwest Regional Climate Center
  2. Hopefully, some rain will return over the next two weeks as forecasted - Source: NOAA CPS


Quick Hits

Large Patch & Spring Dead Spot Prevention Drawing Near

  1. Dry weather has put a halt to early large patch outbreaks. Pics from Spring 2016
  2. Warmer forecasted temperatures may delay spring dead spot applications a bit.

  • On well-irrigated zoysiagrass at our research farm, large patch is still firing, but recent dry conditions have halted symptom development on less watered sites. Additionally, we are slated for a few higher mid-80 to 90+ degree days which should drive a brief flush of zoysia growth. For this reason, fall preventive applications, if they haven’t been made already, may be held off for another week or so until the temperature dips again. The same can be stated for fungicide applications targeted for spring dead spot.  Five-day average 2” soil temperatures have not yet dipped below 70 degrees yet. Although there is no formal threshold model, a common rule of thumb for both diseases is to wait until 2” soil temperatures moderate in the 65-70 degree region to fire away. A subsequent application 21-28 days after the first is suggested on highly amenity sites. Waiting longer into September may be beneficial, since if this fall is like the last, symptoms and perhaps infection of both of these diseases may last into November if winter temperatures again arrive behind schedule.
  • Some diseases on bentgrass putting greens may recur with the impending heat spell. In particular, basal rot anthracnose may rear its ugly head one more time before this season is over.

Seed - Water ≠ Grass

When to Seed Non-irrigated Turf?

  1. Trees are now outcompeting turfgrass for the scarce water supply.
  2. Obvious root competition extending several feet beyond the drip line of trees.

Along with much of Illinois and particularly southeastern Iowa, (see U.S. drought monitor here) the results of little rain over the last 30 days is evident in drought dormant lawns and commercial areas across the region. Tall fescue is particularly primed to deal with the lack of water over extended periods, and is the reason why it’s the main choice for lawns in the region. Of the cool season grasses, tall fescue can best maintain high water potential and reduce water loss in a deficit situation with its extensive root system and stomata regulation (avoidance). Like much of it is doing now, tall fescue can also reduce its physiological processes and go into dormancy with lower tissue water potential (tolerance).

This current drought is producing a problem in seeding or overseeding tall fescue lawns now. We have been in the prime time window for the last three weeks for seeding, but on lawns that were not irrigated establishment will not be optimal. Seed that was put down over the last few weeks and not irrigated, may not just sit there and wait for the rain since a heavy dew set can provide enough water to get germination going. These weaker seedlings wouldn’t have had a chance without supplemental irrigation, so seeding this fall has subsequently required pulling a hose. This is especially true for turfgrass establishment near trees, as shown above.

If you are going to renovate, seed, and fertilize a client’s lawn, make sure they are informed on the necessity and scheduling of irrigation after you leave. Mother Nature may provide some rainfall early next week, meaning this weekend and next week may provide the best window for seeding and renovation with a little help. As we slide into October, establishment becomes more difficult as seedlings need to be mature and hardened off prior to Old Man Winter’s fury. Additionally, fallen tree leaves can provide a humid environment for seedling damping off, so get the spreader going soon while there still is some shade. 


Lee Miller
Follow on Twitter!  @muturfpath
Like on Facebook! Mizzou Turfgrass
Extension Turfgrass Pathologist
University of Missouri