Maintaining a lawn can often seem more complicated than maintaining a garden.
Not only are weeds more likely to appear, but you don’t get the benefit of complementary gardening. So, regular application of herbicides is essential.
Roundup is one of the safest and most trusted names in lawn care. There are several Roundup formulations available, but the most common is Roundup Pro.
The active ingredient in Roundup Pro is glyphosate, a non-selective post-emergent herbicide.
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° and 85°F. But there are some rules to consider.
These relate to 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° and 75°F. 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 of 53°- 85°F, it’s important to note that this covers both day and night temperatures.
Applying Roundup when the daytime high is only 53°F means it will have little to no effect. Likewise, if the nighttime temperature is hovering around 85°F, the Roundup will cook by midday.
In other words, account for a 10° F difference between night and day. Avoid applications when the daytime temperature is below 63°F or the nighttime temperature is above 75°F.
Watch the Temperature Pattern
Roundup takes time to soak in, and weeds become sluggish outside their preferred temperature range.
Apply Roundup only if the lows for the previous two nights have been at least 50°F.
Likewise, the daily highs should be 90°F 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 elevated metabolism will process and distribute Roundup more quickly throughout all plant parts, where it can begin to do its job.
Consider Your Climate
In warmer climates, morning is often the best time to apply Roundup, as midday heat can 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°F.
- The past two days have been no hotter than 90° F.
- Today’s forecast is no colder than 53° F and no hotter than 85° F.
- The day is overcast but not rainy or windy for at least 6 hours.
- Know whether you have warm-season or cool-season grass.