Hort Tips for September

Home Grown  by Keith Reed
September is under-rated as an important time for landscape tasks in Oklahoma. This is the key month to begin preparing plants for the upcoming winter and setting them up for a successful spring. Our recent reprieve from our typical August heat makes the next few weeks especially important from a fall vegetable garden and weed control perspective. The time to act is now! Here are some helpful tips on those areas along with some other suggestions for your September landscape:

  • If you plan on applying fall pre-emergence to prevent pesky spring weeds like annual bluegrass, henbit, chickweed and several others, do it as soon as possible as it’s likely some of these weeds have already popped up thanks to a few rounds of cool nights. The proper product to use can vary depending on a particular application. Contact the Extension office if you need additional assistance. And always remember, these products will fail (or cause damage) if they are not applied properly. Always follow label directions.
  • The window has closed for planting some fall vegetable crops. However, you can still plant spinach, leaf lettuce, mustard, radishes, rutabagas, Swiss chard, garlic and turnips.
  • If you are not planting a fall vegetable crop, consider planting a cover crop. Cover crops build organic matter which in turn leads to improvements in water and mineral holding capacity, improved drainage; critical factors for plant health. OSU Fact Sheet #6436 Healthy Garden Soils is a good resource on cover crops.
  • September is the month to resume lawn fertilization for cool-season grasses (i.e. shade) like tall fescue. This should also be the last month of the growing season to fertilize warm-season grasses like bermuda, zoysia or buffalo. See OSU Fact Sheet #6420 Lawn Management in Oklahoma for more information.
  • Damage from twig girdlers, a common tree pest, can start showing up this time of year. While we usually don’t see the actual insect, their damage is apparent. These pest chew off the ends of small tree branches, leaving an almost machine line pattern of consistency with the cuts. If you start finding branches on the ground with conical shaped cuts on the large end, this is your culprit. These insects don’t really warrant control as is is extremely rare for them to cause significant damage. If you wish to reduce the presence of twig girdlers long-term, it can be helpful to pick up the fallen branches and dispose of them offsite.
  • As you already know, while bermudagrass makes a fine turfgrass for many Oklahoma applications, it can also be a very troublesome weed if it is growing where it does not belong. September is the best time of year to weaken unwanted bermudagrass with the non-selective herbicide glyphosate or a product labeled for control of grassy weeds. Please note that I said weaken not kill. This is a very difficult plant to eradicate once it is well established. Make sure it is not suffering from drought stress before spraying. Also, keep a close eye on it and be prepared to respray as needed later this fall. Even this may not be enough. Keep a close eye out for new growth in the spring and respray/dig out as necessary. While it is not completely impossible to eliminate bermudagrass without using herbicides, it can be done with hard work and patience. We will cover this in-depth in another article.

For more information on this or any other horticultural topic, you can contact Keith Reed, the Horticulturist in the Payne County Extension office. Keith can be reached via email at
keith.reed@okstate.edu, phone at 405-747-8320, or in person at the Payne County Extension office, located at 315 W. 6th in Stillwater.

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