| For the Times-Union
I’m sure winter still seems far off, but in terms of ensuring our lawns come out of the winter looking their best, we have to prepare beforehand. Now, ideally all of the major issues have been covered throughout the year — maintaining proper mowing, fertility and irrigation, limiting weed incursion and controlling any pest and disease issues as they’ve occurred through a vigorous scouting regimen. If that hasn’t been done, there is a good chance the lawn may have large patches of warm-season weeds or bare spots in the lawn that will leave the door open for cool season weeds to settle in next.
While we can’t change the past if we’ve made any lawn mistakes this year, we can move forward and make sure our lawn is as resilient as possible. There are a few things I’d recommend doing.
Many of you have heard of winterizer fertilizers, but be cautious — some of these contain too much nitrogen and may in fact increase lawn susceptibility to cold injury. If you’ve been fertilizing appropriately, now is the time to put out your final fertilizer. Don’t wait much longer or we’ll start to risk both increased chances of cold injury and nutrient leaching.
Fertilizer is always posted with three numbers in front representing the percentage contained of N:P:K. We never want to apply any P (Phosphorus) to our lawns unless a soil test indicates it’s necessary, and if it’s needed you should be applying that in the spring before the rainy season starts. What we’re looking for is a balance between N (Nitrogen) and K (Potassium), either in a 1:1 or preferably 1:2 ratio; the exact mix isn’t an issue, it’s the ratio and the quantity that we apply.
A commonly available fertilizer is a 15:0:15 and that will work fine for this time of year if you can’t find one with a higher ratio of potassium. You may find a 32:0:10 labeled as a fall or winterizer fertilizer, but avoid these if you can; they will promote too much growth without the cold tolerance we get from a higher rate of potassium.
So, how much should you be applying? Apply at a rate of one-half to one pound nitrogen per 1,000 square feet, keeping in mind there is a limit to the amount of soluble nitrogen that can be applied. If you don’t have slow-release nitrogen component, limit your application to no more than 0.7 pounds of nitrogen per 1,000 square feet. If you’ve neglected to fertilize all year, I would recommend limiting your application to the lower end of the spectrum at just one-half pound nitrogen per 1,000 square feet. Make sure to lightly water the fertilizer in.
Another thing we can do if we generally mow low is to start raising that mower up to the highest recommended height for our grass type — 3.5 to 4 inches for St. Augustine or bahia and 2 to 2.5 inches for our zoysia or centipede lawns; this will help add some additional stress tolerance.
The last thing we need to consider is keeping those winter weeds at bay, and the best time to control weeds is before they have sprouted. Competition for resources is the easiest method to limiting weed establishment but as winter approaches the lawn will become less and less competitive.
Again, it’s easier to control weeds before they establish and as such pre-emergence herbicides can often offer the best overall control with the least amount of damage to our existing plants. Such herbicides keep seeds from germinating; and they’re most effective against annual weeds. Post-emergent herbicides are used to kill weeds after they have started to grow and are often more appropriate selections for perennial weeds.
Choosing the right active ingredient, applying it at the right time and at the correct rate are the most important aspects of successful herbicide treatments. Which active ingredient is most appropriate depends on the targeted weed species and the desirable plants that are in proximity to the application area. For example, if we wanted to control Florida betony, we would likely choose a post-emergent herbicide. Compounds such as 2,4-D and dicamba work well and in general can be used on bermuda grass and zoysia lawns, however many formulations of these compounds can cause injury to St. Augustine grass. For St. Augustine grass we may consider an application of Atrazine instead.
You should start planning your winter weed control now; a pre-emergent for cool season weeds in our area should usually be applied in early to mid-October. Of course every year is different so the firm recommendations are for application to occur when night time temperatures stay around 55-60 degrees for three consecutive days. Most applications of pre-emergent herbicides can continue to effectively control most targeted weeds for 6-12 weeks.
Again, the specific compound to apply really depends on the target weeds, particularly if it is a grass, sedge or broadleaf weed. For example, products containing prodiamine, mesotrione or sulfentrazone are generally effective at managing broadleaf weeds such as cudweed or Carolina geranium and are generally safe on a range of turfgrasses. Sulfentrazone is effective at controlling a range of sedges. However, as with any pesticide application, thoroughly read all labels and follow all requirements for safe, appropriate application.
These are just to give examples of the considerations that need to be made. If you’re uncertain of the identity of a given weed or the most appropriate herbicide to apply, reach out to your local UF/IFAS Extension office and they will be happy to offer specific guidance. As always, scout regularly for best results. Have more horticulture questions? Feel free to reach out to the Master Gardener Volunteers at your local county extension office. Contact information for your county can be found at sfyl.ifas.ufl.edu/find-your-local-office/.
Chris Kerr is an environmental horticulture agent with the Duval County Extension Service and the University of Florida/IFAS.