Taking care of a lawn can often seem more complicated than an entire garden.
Not only are weeds more likely to appear, but you don’t get the benefit of complimentary gardening. So regular application of herbicides is a must.
Roundup is one of the safest and most trusted names in lawn care.
There are several formulas of Roundup now available, but the most common one is Roundup Pro.
The active ingredient in Roundup Pro is glyphosate, a non-selective post-emergent formula.
It has such a high track record that failure is almost always user error.
One of the most common errors is applying at the wrong temperature.
What Is the Best Temperature to Spray Roundup?
Roundup works best between 60° – 85° degrees Fahrenheit. But there are some rules to consider.
These have to do with the seasonal type of turfgrass and the time it takes for Roundup to take effect.
Grass Seasons
There are two main categories of turfgrass: cool-season and warm-season.
Cool-season species grow best at temperatures between 60°- 75° degrees Fahrenheit. They become sluggish at colder temperatures.
Warm-season species-like temperatures around 80°- 95° degrees Fahrenheit.
It’s important to note which type of turfgrass you have. It affects both when to apply fertilizer and when to use certain herbicides.
Roundup will combat a wide range of weeds and broadleaf plants. They often appear at the same time your grass does, having similar temperature preferences.
Thus, you can gauge the temperatures your weeds will enjoy by when your turfgrass grows.
Day Temps vs. Night Temps
With a temperature range as wide as 53° – 85° degrees Fahrenheit, it’s important to note that the range covers both day and night temperatures.
Applying Roundup when the daytime high is only 53° degrees Fahrenheit means it will have little to no effect.
Likewise, if the nighttime temperature is hovering around 85° degrees Fahrenheit, the Roundup will cook by midday.
In other words, account for a 10° degrees Fahrenheit difference between night and day.
Avoid applications if the daytime temperature is below 63° degrees Fahrenheit or the nighttime temperature is above 75° degrees Fahrenheit.
Watch the Temperature Pattern
Roundup takes time to soak in, and weeds become sluggish outside their preferred temperature range.
Only to apply Roundup if the lows for the previous two nights have been at least 50° degrees Fahrenheit.
Likewise, the daily highs should be 90° degrees Fahrenheit or below for at least two days. And your lawn must be getting enough water.
But why is this important?
Roundup fits into a category known as contact killers.
The herbicide absorbs directly into the weed’s foliage, making contact there instead of through the soil.
When a weed is sluggish, it takes longer for the herbicide to absorb and spread throughout the plant’s body, rendering it less effective.
But if you catch the weed when it’s most active, it’s like eating food after a good run. The heightened metabolism will process and distribute the Roundup more quickly to all plant parts, where it can begin to do its job.
Consider Your Climate
In warmer climates, morning tends to be the best time to apply Roundup, as the midday heat will often cause weeds to take a short siesta.
But in cooler climates, it works best when applied during midday. Take care not to wait until evening when the dropping temperatures may put the weeds to bed for the night.
The Quick Version
Plan your Roundup applications to meet the following criteria:
- The past two nights have been at least 50° degrees Fahrenheit.
- The past two days have been no hotter than 90° degrees Fahrenheit.
- Today’s forecast is no colder than 53° degrees Fahrenheit and no hotter than 85° degrees Fahrenheit.
- The day is overcast but not rainy or windy for at least 6 hours.
- Know whether you have warm-season or cool-season grass.