Garden Tips for September

David Hillock


  • Watch for fall specials at garden centers and nurseries since fall is a great time for planting many ornamentals.
  • Choose spring flowering bulbs as soon as available.
  • Plant cool-season annuals like pansies, ornamental cabbage or kale, snapdragons and dusty miller when temperatures begin to cool.
  • Watch for and control any late infestations of tree webworms.
  • Twig girdler insects should be controlled if large numbers of small branches of elms, pecans, or persimmons are uniformly girdled from the tree and fall to the ground.
  • Begin to reduce the amount of light on outside tropical houseplants by placing them under shade trees before bringing them indoors for the winter.


  • You have all of September to plant cool-season vegetables like spinach, leaf lettuce, mustard and radishes, and until the middle of September to plant rutabagas, Swiss chard, garlic and turnips.


  • Last nitrogen fertilizer application of the year on warm-season grasses should be applied no later than September 15. (HLA-6420)
  • Winter broadleaf weeds like dandelion will begin to emerge in late September, which is also the best time to control them with a 2, 4-D type herbicide.
  • If pre-emergent control of winter-annual weeds (henbit, chickweed, annual bluegrass, etc.) is desired in lawns, the application should be completed by the second week of September. Note: Do not treat areas that will be seeded in the fall.
  • Continue bermudagrass spray program with glyphosate products for areas being converted over to tall fescue this fall.
  • Plan to seed bluegrass, fescue or ryegrass as needed in shady areas in mid- to late-September. Fall is the best time to establish cool-season lawns (HLA-6419).
  • White grub damage can become visible this month. Apply appropriate soil insecticide if white grubs are a problem (EPP-7306). Water product into soil.

Fall is for Planting Trees and Shrubs

David Hillock

Fall is an excellent time to plant most trees and shrubs. In fact, research suggests that early fall planting is best for container-grown and B&B shade and ornamental trees and pines, but spring is best for planting bare-root plants and broadleaf evergreens, such as holly and Southern magnolia. Plants planted in the fall have more time for the root system to become established before the onset of summer heat. Plants installed during the growing season are susceptible to high transpiration rates leading to drying of plant tissues.

A perfect example of this was seen at the Oklahoma Gardening© Studio Gardens several years ago when we planted the Edible Landscape bed. One blueberry shrub was planted in the fall and then several more were planted in the spring. There was a noticeable difference between the one planted in the fall and those planted the following spring; in spite of the heat the fall planted shrub looked awesome and was barely phased by the extreme temperatures that summer. The others struggled, having crispy leaves, dropping many of them, and barely hanging on in spite of the intense watering provided to keep them alive.

 So, if you need to replace a tree or shrub or want to add more to the landscape, now is the time to be looking for that perfect plant. The weather should be changing for the better as we move through the month of September, bringing cooler temperatures and additional rainfall, something we all will eagerly welcome and our plants will greatly appreciate.

Cool-season Lawn Planting and Renovation

David Hillock and Dennis Martin

The period mid-September through early October in Oklahoma typically has near-ideal day/night temperature combinations for germination of cool-season grasses. So, let the tall fescue, perennial ryegrass and Kentucky bluegrass seeding begin (if you have access to water)! Sodding of these grasses is also appropriate at this time. The best temperatures for germination are when we experience a mid-80s day and upper 50s/low 60s night. You might be asking, is it possible that we will get fooled and the temperatures will shoot back up. Sure, anything is possible in Oklahoma, but what is key to remember is that the night time lows are what’s important. When you see evening temperatures from the upper 50s to mid-70s, it’s time to seed cool-season lawns. So even if a few day-time highs slip back in the mid to upper 90s, (and it will happen) our day-time lows are looking great!

Fact sheet HLA-6418 covers turfgrass selection, while HLA-6419 covers the establishment (planting method) and HLA-6420 covers the mainstream long-term maintenance practices (mowing, fertilization, irrigation, etc). A newer fact sheet, HLA-6608, addresses managing turfgrass in the shade. Find these on the web at the turf collection located at:

There are many satisfactory performing tall fescues. These include, but are not limited to Crossfire II, Houndog V, Millenium, Rembrandt, Plantation to name just a few. There are dozens of good performers. A blend is a combination of two or more varieties within the same species. A mix is two or more species combined. Blends and mixes are beneficial in cool-season lawns as they broaden the genetic diversity present. In theory, this decreases the likelihood that your lawn will be completely wiped out by a single disease or single insect infestation.

Most importantly, if turf-type quality is expected, choose a turf-type rather than a forage type tall fescue. Forage type fescues include Fawn and Alta. General purpose soil stabilizer types include the old K-31, Kentucky 31, KY 31, they get used as a forage and as a lawn, but these variations on Kentucky 31 are not true turf-type tall fescue despite what the marketing message on the seed bag might say. Turf-types are selected for improved color, texture, density, slower vertical leaf expansion rate and other important characteristics for lawn use.

Tall fescues are best in medium to light shade. There are no hard and fast rules for “hours of sunlight” required. There are no perfect solutions to dense shade where grasses fail repeatedly, year-in and year-out. It is best to take a hint if grass is failing in a shaded site many years, it’s time to move on to mulches, shade tolerant perennial ground covers, hardscape elements, etc.; a list of alternate shade tolerant plants can also be found in fact sheet HLA-6008. Sometimes grass does not die exclusively from shade, but rather the combination of shade and tree root competition for nutrients and water in combination with added disease pressure due to less air movement and more grass canopy moisture caused by less air movement in a “tight and mature” landscape.

In lightly shaded areas, mixtures of tall fescue and Kentucky bluegrass can sometimes work best. While Kentucky bluegrass is generally not as shade tolerant as tall fescue, it still has some shade tolerance and it has improved brown patch disease and Rhizoctonia blight resistance over that of tall fescue. Brown patch is usually the most serious disease of tall fescue. These mixtures will often have Kentucky bluegrass present at 5 to 10% by weight and tall fescue at 90 to 95%. There are 10 times as many bluegrass seeds in a pound of bluegrass as there are tall fescue seeds present in a pound of fescue so we use about 10 times less bluegrass seed to get to a 50/50 species count. Never, use a 100% stand of Kentucky bluegrass in most areas of Oklahoma because pure stands of Kentucky bluegrass in most of Oklahoma can get summer patch disease. Also, older Kentucky bluegrasses such as Park, Newport, South Dakota Common (SD Common), Kenblue and variety not stated (VNS =when there is no variety name stated) really don’t bring any value to the cool-season mix. So if these are the only ones available locally, you might as well use 100% tall fescue. Most other varieties of Kentucky bluegrass that you might encounter (there are hundreds nationally, and yet few repeatedly available in OK from year to year) are improvements and will benefit the mix!

 There is seldom any benefit and there is often detriment created by mixes of cool-season perennial grasses with annual or Italian ryegrass. Yet, if you scout the store shelves, you will find these mixes. Annual ryegrass simply competes with the cool-season perennial grasses in the mix in the cool portion of the year when good growth can take place and then annual ryegrass, having taken its fair share of the lawn, dies out in the heat. This leaves uniformed consumers in a panic at worst and with unsightly dead areas in their remaining cool-season perennial lawn at best. Avoid mixes of annual ryegrass with the desirable cool-season perennials like tall fescue, perennial ryegrass and Kentucky bluegrass.

Collecting and Using Landscape and Garden Waste

David Hillock

It won’t be too much longer and landscape and garden cleanup will be underway. It is recommended that most of the landscape waste be composted and used as an amendment to improve soil conditions. Composting yard waste keeps it out of the landfills, saving time, space and money for the waste collection systems and you.

Leaves are best handled through composting. To eliminate grass clippings, check out the “Don’t Bag It” program through your local Oklahoma Cooperative Extension Service office. Other plant material such as that from the garden or prunings can also be composted. Some items may need to be ground or chipped up first to decompose more quickly.

Below is a quick recipe for making a good compost pile. For more information about composting see HLA-6448 Backyard Composting in Oklahoma.

How to Make Compost

A compost pile is built by layering organic materials. Compost piles should be 3 to 4 feet wide and 3 to 4 feet high. This volume allows the pile to heat as composting occurs.

  1. First Layer: 3 to 4 inches of dried organic matter, such as leaves or dried grass.
  2. Second Layer: 3 to 4 inches of green material, such as kitchen vegetable scraps, grass clippings, or green plant material.
  3. Third Layer: 1 to 2 inches of manure or 1 cup of fertilizer containing nitrogen.
  4. Fourth Layer: 1 inch of soil to add microbes to the pile or a commercial compost starter.

 Do not add pet manure, meat scraps, fat, bones, diseased plants, or noxious weeds to the compost pile.

Controlling Winter Annual Weeds

David Hillock

If winter annual weeds, such as henbit and annual bluegrass, have been a problem in the past then you will for sure want to apply a preemergence herbicide as soon as possible. Many of our winter annual weeds germinate in the fall or early winter and survive as very young plants until late winter or early spring when conditions are more favorable for growth. Waiting until you notice them is too late.

The key to effective control is timing. Preemergence herbicides must be applied well in advance of the expected germination time of the weeds to be controlled. In addition, the products must be watered in to activate them. At least ½ inch of water either through rainfall or irrigation if no precipitation is expected within a couple days after application is recommended. In some cases the product needs to be incorporated into the upper surface of soil.

There are several products available in the garden centers that will effectively control germination of most winter annual weeds. Some are labeled just for turf areas and some are labeled for both turf and ornamental areas. Two products, one containing benefin + oryzalin and the other bensulide, are labeled for use in lawn and ornamental areas. Another product available that contains trifluralin can be used in ornamental and vegetable beds.

Be sure to read and follow the label directions for best results and to avoid damaging any desirable plants.  

2017 4-H State Judging Contest

Shelley Mitchell

The 4-H State Horticulture Judging Contest will be held Saturday, September 30 as part of the 4‑H Judging Contest. The complete list of plant specimens can be found at Note that this year there is a new category of turfgrasses and weeds. For questions, contact Dr. Shelley Mitchell at

Upcoming Events

Fall Pecan Field Day Set for September 22

Knight Creek Farms near Sapulpa will host an upcoming field day for interested pecan growers. This event will showcase topics like early pecan harvest and drying operations; row harvesting; new planting and irrigation options; wildlife control options; and marketing.

The field day is scheduled to begin at 2 p.m. on Friday, September 22 and dinner will begin at 6 p.m. sponsored by Grissoms John Deere. Directions – From Highway 117 in Sapulpa, 6 miles south on S. Hickory St., turn right onto W 181st St S.  Event is free, but registration is required.  Please call (405-744-5404) or email ( to register.

This event is presented by Oklahoma State University Horticulture and Landscape Architecture Department, Noble Research Institute and Oklahoma Pecan Grower’s Association. 

Viticulture & Enology Workshop Scheduled October 24

A special workshop will be held at Waddell’s Vineyard & Winery near Ada on October 24. Registration for the event will begin at 8:30 a.m. and the presentations will commence at 9 a.m. Featured speakers from Texas AgriLife Extension program include Dr. Justin Scheiner and Michael Cook.

Dr. Scheiner will be making a return appearance to share expertise on many applicable topics for our Oklahoma growers. He was a favorite presenter at a 2014 advanced training workshop. Michael Cook is located out of Denton, Texas and has been spending some quality time in some of our Oklahoma vineyards lately. He has provided consultations to vineyards that had requested site visits through an Oklahoma Grape Industries Council grant. The OGIC grant as well as the grant for this workshop was made possible through the ODAFF Viticulture & Enology Fund. 

Some possible topics for the day’s workshop include Grape Cultivar Selection, Fruit & Foliar Diseases, Understanding Vineyard Fungicides, and Grapevine Nutrition. Many of the topics will address challenges that vineyards are encountering as observed by Michael Cook on his site visits. This will be an excellent learning opportunity and will benefit all grape growers. An agenda will be available soon with more details on how to register for this free workshop. Lunch will be catered so an accurate count of those planning to attend will be helpful.

SAVE THE DATE – March 8, 2018 for a Horticulture “Spray Day”

A new horticultural event is in the planning stage that will be focusing on spraying, including fungicide, insecticide, and herbicides. This event will be held at the Cimarron Valley Research Station and open to anyone interested. Emphasis will be on equipment demonstrations for different crops and different sizes of operations; question and answer times; sessions on calibration, worker protection standards, pesticide certification requirements and pest management.  We hope to have vendors with different types of equipment and chemical representatives in attendance. Sponsored by Oklahoma State University Horticulture & Landscape Architecture Department, Oklahoma Field Research Service Unit, Noble Research Institute, Oklahoma Pecan Growers, Oklahoma Grape Industries Council, and Oklahoma Fruit & Vegetable Growers.




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