ATA Turf Times – Dave Han, Ph.D. Auburn University and Alabama Extension
Anyone who has ever managed turfgrass, whether in their own lawn or professionally, will have lots of questions. In my experience, the word that pops up most frequently in questions about turf management is “when.” We’ve all asked or been asked: When should I fertilize? When do I put out my preemergence herbicide? When is the right time to sprig / seed / sod? When should I take a soil test? When should I irrigate? The list goes on.
With so many questions related to timing, calendars are a very popular product to remind people when to do certain things. Calendars can be very useful, but they are not foolproof. Mother Nature does not always provide weather that fits the calendar date, and since so many decisions about turf management are driven by temperature, rainfall and humidity (or should be), there is no substitute for looking at actual thermometers and rain gauges before making decisions. But what I think can be more valuable is a general seasonal guideline of what to expect, what to look out for, and how to plan so when a particular season comes around, turf managers are making good decisions on a monthly or weekly time scale.
Since the Alabama turfscape is dominated by warm-season grasses, this article will focus on those.
 
SPRING
Spring is usually the hardest season to deal with because it brings unpredictable weather. Wild temperature swings, severe weather outbreaks, and a human tendency to want to rush things can all lead to making some bad calls when it comes to spring turf management. Spring is the season when warm season grasses begin their growth after dormancy or semi-dormancy in the winter, when summer annual weeds begin to germinate, and when winter annual weeds are their most noticeable and troublesome. It is also when plans should be made to plant sprigs or seed of warm season grasses.
The main factors to consider in the spring are:

* When to apply postemergence herbicides to control winter annual weeds
* When to apply preemergence herbicides for summer annual weed control
* When to begin fertilizing the turfgrass

All of these decisions will be influenced heavily by air and, especially, soil temperatures. Table 1 provides an overview of some important soil temperatures that affect management decisions. Timing becomes tricky, as soil temperatures will vary wildly from year to year, and even swing up and down within weeks during any given spring. What happened last year may not have much to do with the appropriate timings for this year’s management decisions, especially when it comes to herbicide treatments.
Table 1. Key 4-inch soil temperatures for turfgrass management decisions

Event
Soil Temperature (F)

Crabgrass seed germination
55° – 65°

Warm season grass spring greenup
55° – 65°

Goosegrass seed germination
65° – 75°

Bermudagrass and centipedegrass seed germination
70° and up

Significant root and rhizome growth for warm season grasses
70° and up

Summer annual broadleaf weed germination
70° and up

Ryegrass seed germination
60° – 70°

Poa annua seed germination
50° – 80°

Sources: Turgeon & Kaminski (2019), McCarty (2011), Turgeon (2004)
Preemergence herbicides should ideally be made before the conditions are right for weed seed germination. Some years, the soil will warm quickly and applications will need to be made in January. Other years, they may wait until late February. Also, since there is such a variety of soil temperatures at which various weeds germinate, multiple applications of preemergents may be needed depending on which w...