March HortTips


David Hillock

Lawn and Turf 

  • Remove excessive thatch from warm-season lawns.  Dethatching, if necessary, should precede crabgrass control treatment. (HLA-6604)
  • Broadleaf weeds can easily be controlled in cool-season lawns at this time with postemergent broadleaf herbicides. (HLA-6421)
  • Preemergent crabgrass control chemicals can still be applied to cool- and warm-season turfgrasses (HLA-6421).  Heed label cautions when using any weed killers near or in the root zone of desirable plantings.
  • March is the second best time of the year to seed cool-season turfgrass; however, fall is the best time to plant. (HLA-6419)
  • Cool-season lawns such as bluegrass, fescue and ryegrass may be fertilized now with the first application of the season.  Usually, four applications of fertilizer are required per year, in March, May, October and November. (HLA-6420)
  • Begin mowing cool-season grasses at 1½ to 3½ inches high. (HLA-6420)

Flowers and Vegetables

  • Cultivate annual flower and vegetable planting beds to destroy winter weeds.
  • Apply mulch to control weeds in beds.  Landscape fabric barrier can reduce the amount of mulch but can dry out and prevent water penetration.  Thus, organic litter makes the best mulch.
  • Prune roses just before growth starts and begin a regular disease spray program as the foliage appears on susceptible varieties. (HLA-6403 & EPP-7607)
  • Avoid excessive walking and working in the garden when foliage and soils are wet.
  • Start warm-season vegetable transplants indoors.
  • Divide and replant overcrowded, summer and fall blooming perennials.  Mow or cut back old liriope and other ornamental grasses before new growth begins.
  • Your cool-season vegetables like broccoli, cabbage, carrots, lettuce, onion, peas, spinach, turnips, etc. should be planted by the middle of March.
  • Watch for cutworms that girdle newly planted vegetables during the first few weeks of establishment.  Cabbage looper and cabbageworm insects should be monitored and controlled in the garden (EPP-7313).

Trees and Shrubs

  • Prune spring flowering plants, if needed, immediately following their bloom period.
  • Plant evergreen shrubs, balled and burlapped, and bare root trees and shrubs.
  • Anthracnose control on sycamore, maple and oak should begin at bud swell. (EPP-7634).
  • Diplodia Pine Tip blight control on pines begins at bud swell. (EPP-7618)
  • Chemical and physical control of galls (swellings) on stems of trees should begin now. (EPP‑7168 & EPP-7306)
  • Dormant oil can still be applied to control mites, galls, overwintering aphids, etc. (EPP-7306)
  • The first generation of Nantucket Pine Tip Moth appears at this time.  Begin pesticide applications in late March. (EPP-7306)
  • Control Eastern tent caterpillars as soon as the critters appear.


  • Continue to plant strawberries, asparagus and other small fruit crops this month.
  • Start your routine fruit tree spray schedule prior to bud break. (EPP-7319).
  • Remove winter mulch from strawberries in early March (HLA-6214).


Irrigation System Maintenance:  Spring Start Up

by David Hillock

Now is a good time to prepare your irrigation system for the season.  Before turning it on make a visual inspection of the sprinkler heads.  Check for broken heads or covered up heads; free heads, make height adjustments, and be sure spray heads are still in the correct position.  Check all valve boxes for rodent nests and debris.

Make sure there is power to the controller and set stations for proper run times.  Turn the main water source on slowly to fill the system.  If you have manual drain valves, leave them open to allow air to escape as the pipes fill with water; when water starts coming out the drain valves, close them.  Turn on each station manually and check for leaks, all heads are providing adequate coverage to their area, and are closing properly.  If the system is not running properly, additional troubleshooting should begin and repairs made.  If major issues are discovered, an irrigation specialist may be needed to fix the problems.

If you don’t already have a rain sensor on your system, now would be a good time to install one. Replacing backup batteries could also be done at this time.

Making sure the system is running properly and efficiently now will ensure your landscape plants will be healthy going into the growing season.

Is it too late to apply glyphosate herbicide for winter annual weed control in bermudagrass?

by Dennis Martin

Glyphosate, the active ingredient in the popular herbicide product Roundup Pro and certain similar product, can sometimes be used over completely dormant bermudagrass for winter-annual weedy grass control.  With a broadleaf post-emergent tank-mix partner, the tank-mix can often be used for both winter annual grassy and broadleaf weed control in dormant bermudagrass.  But, how do you know if it is too late in winter to effectively use a glyphosate containing herbicide for weed control without damaging your bermudagrass?  You have to scout the area to make sure conditions are still suitable for this application!!!  That’s the only sure way to know!

Excerpt from the Roundup Pro label – “Dormant Turfgrass – This product may be used to control or suppress many winter annual weeds and tall fescue for effective release of dormant bermudagrass turf.  Treat only when turf is dormant and prior to spring greenup.”

Here are some tips for successfully using the glyphosate application over dormant bermudagrass while minimizing risk of bermudagrass injury:

  1. First, walk over the bermudagrass stand and closely observe from just above the bermudagrass leaf canopy just minutes before you make the herbicide application to ensure the stand is totally dormant and that no live bermudagrass shoots are popping through the canopy!  Do you see any live green, red or purple bermudagrass leaves or shoots?  While you might part the tan canopy with your hands just to see if the bermudagrass is alive below, it is the solid tan canopy viewed from above that shields the live material below from intercepting spray droplets.  Hopefully you will always be able to see live bermudagrass tissue in the lower canopy (if you part the canopy) that is being shielded by the dead, tan leaf canopy.  Without live tissue being contacted by the spray solution, the plant will not take up and will not be injured by the application.  If you see openings in the canopy from above where the bermudagrass leaf canopy is not thick, dense and tan, and if it’s not providing 100% shielding, then there is risk of injury from the glyphosate spray solution.  BE THE SPRAY DROPLET!  When scouting is done properly, you are essentially pretending you are the spray droplet.  Are you contacting any bermudagrass tissue?  Yes or No?  If yes, then don’t spray that area with glyphosate!
  2.  Remember, the application is really not labeled for high quality turfgrasses other than bermudagrass.  While some people may use this application over dormant zoysiagrass, it’s not labeled for that use, so don’t apply glyphosate over zoysiagrass.  Also, never use this application over any desirable cool-season turfgrasses!
  3. Not all glyphosate herbicide products are labeled for use in this application even though they might contain the same active ingredient.  This is called “product label use-site specificity.”  It is the applicators’ responsibility to read the label and ensure that the product is labeled for this specific use and that the label is followed to the letter and thereby following the letter of the law!
  4. Use only the correct product labeled for this application and use the correct use rate and the correct carrier rate!  I mentioned this in point number 3 above but it is worth mentioning again!
  5. Don’t over use either the use rate or the carrier rate.  Remember, if you over apply the spray volume and exceed the 10 to 40 gallon per acre carrier rate, the spray droplets may roll down the stem by gravity and contact the live green, red or purple stems below.
  6. The application is best made when temperatures are in the 60s but definitely prior to bermudagrass green-up.  By the time air temperatures are in the 60s, winter annual weeds are generally metabolically active and are more effectively controlled by this application.

Winter annual weeds, left untreated, are often responsible for up to five early-season lawn mowings that occur before the bermudagrass actually needs mowing.  The use of glyphosate for winter annual weed control in dormant bermudagrass is a very useful and reliable tool with manageable risk when the practice is executed responsibly.  Remember to read and observe all pesticide label directions.

2014 Perennial Plant of the Year™

David Hillock

‘Northwind’ switch grass was selected as the Perennial Plant Association’s 2014 Perennial Plant of the Year™.  Switch grass, Panicum virgatum, is also the perennial for the Oklahoma Proven Plant Selection this year with ‘Northwind’ suggested as one of several cultivars available that will grow well in Oklahoma.

Roy Diblik selected ‘Northwind’ from a population of Panicum virgatum he raised using wild-collected seed from plants growing along railroad tracks in South Elgin, Illinois.  In July 1983, he noticed that one plant had wider leaves and a very upright growth habit, unlike the typical arching form of the others.  He gradually built up stock of the upright one.  In 1992, when Northwind Perennial Farm opened, he introduced it and named it ‘Northwind’. 

Panicum virgatum ‘Northwind’ spreads slowly to form erect clumps of slender, steel-blue leaves about five feet tall.  In late summer, the foliage is topped by a haze of showy, finely-textured flower panicles that rise to six or even seven feet, and that open golden yellow and mature to beige.

Deep roots make ‘Northwind’ remarkably drought-tolerant, once established.  And like most ornamental grasses, Panicum virgatum ‘Northwind’ is seldom eaten by deer.


Camp T.U.R.F. (Tomorrow’s Undergraduates Realizing the Future)

Shelley Mitchell

The fifth annual Camp TURF (Tomorrow’s Undergraduates Realizing the Future) is scheduled for June 1-13, 2014.  The two-week residential summer academy is sponsored by the Oklahoma State Regents for Higher Education, and students attend at no cost to themselves.  Eligible students are Oklahoma residents entering 9th or 10th grade in the fall of 2014.  Camp TURF is an opportunity to explore the fields of horticulture and landscape architecture with hands-on activities led by professors.  Activities take place in design studios, greenhouses, laboratories, botanic gardens, arboretums, and classrooms.  Each evening, scheduled recreation activities include bowling, swimming, canoeing, local theatre productions, etc.  Evening meals are at local restaurants such as Eskimo Joe’s.  Students live in the residential suites on campus for the entire two weeks.  For more information, contact Dr. Shelley Mitchell,, 405-744-5755.


 Herbaceous Plant Materials Conference

July 17, 2014
Wes Watkins Center – Stillwater, OK

 Greenhouse Production Conference

September 11, 2014
Wes Watkins Center – Stillwater, OK


September 20, 2014; 10 AM – 4 PM
The Botanic Garden at OSU – Stillwater, OK

 The Botanic Garden’s Annual GardenFest brings together individuals from across the state with a common interest in gardening and sustainable living for a day of educational workshops, tours and activities for the whole family.  It is also a wonderful opportunity to view the beautiful landscapes and innovative demonstrations throughout The Botanic Garden at OSU while experts are on hand to answer questions.  Live music and vendors will be featured along with our educational programming.

 Global Horticulture Conference

November 6, 2014
Wes Watkins Center – Stillwater, OK

 For more information about upcoming events, please contact Stephanie Larimer at 405-744-5404 or


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