The Soil Temperature in your lawn, not calendar dates, is what should be used to determine your lawn care schedule.
How do you know when to start your lawn care program? Or when to apply seed, or pull the trigger on that fall renovation?
Many homeowners rely on taking cues from the big box stores. If this product is on the shelf, it must be time to apply it, right? Some people may look for specific calendar dates for guidance. Or maybe you simply wait until you have time to get out in the yard, or even better, you’re waiting for a nice day when you actually feel like doing some yard work.
The problem is, your lawn doesn’t care about calendar dates, and it certainly doesn’t care about when it’s convenient for you to apply product to your lawn. When it’s time for weeds to germinate, weeds will germinate. When your lawn needs fertilizer, it needs fertilizer.
So what is the driving force behind everything that happens in your lawn? The answer is Soil Temperature!
Instead of calendar dates, let’s take a look at the most important soil temperature thresholds and what’s happening to your lawn when soil temps hit those thresholds.
Since cool season lawns and warm season lawns have slightly different things happening at different soil temperatures, this post is divided into a Cool Season section and a Warm Season section.
Also you may be wondering how to get soil temperature data. This will be covered at the bottom of the post where I discuss the 2 simple tools I use to obtain soil temperature data for my lawn.
Important Cool Season Lawn Soil Temperatures
55 Degrees
Think of 55 degrees as being go time. This is when cool season grasses start to wake up in the spring. It’s also when broadleaf weeds such as crabgrass begin to germinate. Since 55 degrees is go time, you want to time your first fertilizer application, as well as pre emergent application so that these products are already in the soil by the time it hits 55 degrees.
To achieve this, you need to apply your pre emergent and fertilizer when soil temps average 50 degrees for 24 hrs.
If you’re looking for an easy lawn care program to follow check out this post: Lawn Care Program for Extra Green Grass. You’ll learn more about which products to use.
While 55 degrees might be go time in the spring, it means the opposite in the fall. When soil temps head below 55 it means the season is winding down and chances are there’s probably another couple of mowing days left. This is when you want to get ready to apply a Winterizer Fertilizer.
65 Degrees
This is around the time when your cool season grass is happiest. It has fully woken up and is pushing green blade growth like crazy. This is when you want to mow as much as possible! It might sound like a lot of effort but mowing at least twice a week during this time is so much better than once a week. This is also a good time to start spot spraying for dandelions which tend to pop up at this time.
70 Degrees
70 degrees is an important soil temperature in the spring, and also in the fall as soil temps begin to cool after the summer soil temperature peaks.
In the spring, 65-70 degrees is when you want to apply a second round of pre-emergent herbicides and also another shot of fertilizer. Think of this as your ‘step 2’.
This gives you much more even, long lasting protection from annual weeds such as crabgrass that will continue to germinate at this temperature range. Also, continue to spot spray for any weeds that have already germinated. No pre emergent program is perfect, so there could still be plenty of weeds that need to be spot treated.
After the heat of the summer, 70 degrees is once again an important threshold to look for. This is when fall broadleaf weeds such as henbit and chickweed germinate. It’s also when Poa Annua germinates. That’s why I recommend applying pre emergent for a third time as temps head back down to this 70 degree range.
It’s important to point out if you plan on doing any fall seeding in your lawn then don’t apply any pre emergent when soil temps come back down to 70 degrees.
Instead start preparing your lawn for fall renovations such as Core aeration and Overseeding, Top dressing, or Dethatching. The 70 degree threshold at the end of summer is when you want to pull the trigger on your seeding projects if you have any.
80 Degrees
80 degree soil temperatures are a rough time for your cool season grasses. If they don’t receive adequate water at this point then they will likely head into a period of dormancy.
At this point, soil temps are too hot for weed seeds to germinate, however any weeds such as crabgrass that have already germinated will thrive during these hot weeks. That’s why it’s so important to do the work before soil temps hit 80. At this point you want to really back off on using high nitrogen fertilizers, especially if you don’t have an irrigation system. You should also increase mowing height and make other preparations for your Summer Lawn.
Important Warm Season Lawn Soil Temps
55 Degrees
Just like cool season lawns, 55 degrees marks the beginning of your lawn care season. This is when broadleaf weeds such as crabgrass start germinating.
As soil temps start increasing in late winter you’ll want to be ready to go when soil temps approach 55 degrees. This is when you should apply your pre-emergent herbicide. You’ll actually want to throw your pre-emergent down when soil temps are averaging 50 degrees so the product is in the lawn already before averaging 55 degree soil temps.
Unlike cool season grasses, it’s not quite time to fertilize your warm season grass yet. These grasses like the heat, so they don’t get going until higher soil temps. So for now, lay off the nitrogen fertilizer.
In the fall, 55 degree soil temps will mark the end of your lawn care season. At this point your warm season grass will not need mowing and depending on the weather and your region, your warm season lawn might start heading into dormancy.
65 Degrees
When soil temps hit 65 degrees, this is when warm season grasses start growing. Now is when you’ll be mowing, probably pretty often (twice a week). This is when you should apply your first application of fertilizer. It’s also when you want to apply your second application of pre-emergent.
70 Degrees
Heading into spring/summer, once the soil temperature hits 70 degrees, your warm season lawn should be fully awake and actively growing.
The next time you want to look for the 70 degree threshold is after the heat of the summer when soil temperatures start to head back down to 70. That’s when a third round of pre emergent herbicides should be applied to prevent fall germinating lawn weeds.
80 Degrees
Once soil temps hit 80 degrees, warm season grasses thrive. Unlike cool season grasses, warm season grasses like the heat. This is when you want to feed the lawn plenty of nitrogen fertilizer to push it to get thick.
How to Find Soil Temperatures
I use a combination of 2 tools to determine soil temps in my lawn. For starters, I check out Greencastonline. This is a great website where you can put in your zip code and get the latest soil temp averages in your region. I usually look for the 24 hour average.
The other tool I use is a soil thermometer. I simply stick this down about 3” and check on it daily when I know its getting to be the time to take action.
It’s important to realize though, these thermometers do spike during the heat of the day and cool during the night. This is where you have to play detective. I don’t rely solely on the soil thermometer, nor do I rely solely on Green Cast Online. I gather information from both and use that determine when it’s time to get things started.
You’d be surprised at how we all live in little micro climates. For example, I live at the base of a mountain and can have very different weather than a couple miles down the road. I like knowing that I can take soil temps in my own yard and compare it to soil temps reported in other areas.
The last thing I’ll say as it relates to timing is always error on the side of too early. Meaning, you’re better off applying pre emergent herbicides, or fertilizer, or any other application (ie. insects or fungus) too early than too late. Most products take some time to get into the soil and hang around for awhile once there.
Check Out These Posts Next
3 Product Lawn Care Program- Cool Season Lawns
Lawn Care Program for Warm Season Lawns
Cool Season Grass Vs. Warm Season Grass
Winterizer Fertilizer: Everything You Need to Know
Top Dressing Lawn: Benefits and Advice
Lawn Dethatching: Everything You Need to Know
White Grubs: Prevention and Treatment
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Thanks for the great info! I think I’ve been applying my pre emergent too early. I’m going to be more patient this year and track soil temperatures. I had a lot of crabgrass last year. I love the idea of doing a split pre emergent app in the spring.
I found this interesting article while browsing Pinterest. I appreciate the education to properly maintain my lawn. I have recently retired and am willing to do the work but I needed the step by step information to tackle my problem lawns. Where should I start to look for the Lesco Dimension Crabgrass Pre-emergent in my area ( North-West Wisconsin)? Also, I have a problem with mushrooms proliferating in an area of my lawn near an Ash tree in the last 3-4 years. My lawn has a sprinkler system. No one can give me answers as to how to resolve this problem. Do you have any suggestions?
Hi Sheryl! I’d recommend checking out Home Depot online and looking up the product. You might be able to get it shipped to your local store. In not, check out the section where I talk about some substitutions in my post Lawn Care Schedule Using 3 Products. As for the mushrooms, it is most likely Ash Tree Bolete, which is a common mushroom found under Ash Trees. They actually have a symbiotic relationship with the Ash Tree. The mushrooms take in carbohydrates from the roots and the mushrooms help the roots absorb nutrients. To my knowledge there is no real good way to prevent them from coming back. Of course, you can always manually remove them, but that is temporary. I wouldn’t bother with fungicides since that won’t be effective either.
Hello Mark, another great article! I plan to follow the “3 products” schedule this year and currently prepping to put down my first application of Lesco 19-0-7. Out of curiosity, is it ok to wait until the 5-day (ground temp) average first reaches 50 degrees or is it best to stick to the 24-hour average? I ask because here in Charlotte (NC), our ground temps tend to jump all over the place, especially in Jan/Feb — ground temp could be 50 for a couple of days, then drop to 30s & 40s for a week, etc. Just looking for a little clarity on the best strategy.
Wow, this is so informative, helpful AND hopeful! After paying a small fortune to lawn service providers for lackluster results, I am educating myself in preparation for taking over my Lawncare. I will definitely follow your advice and recommendations. Thank you!
I am, however, battling creeping bentgrass and have found that the product Tenacity is most often recommended for pre- and post-emergence control of CBG. Will your recommended Lesco Dimension 19-0-7 provide control of CBG? Or, since Tenacity is not a fertilizer, may it be used in combination with Lesco Dimension? Any help will greatly appreciated.
Hi Pamela! Happy to hear you found the content helpful! So if you already have creeping bentgrass, a preemergent like the Lesco 19-0-7 won’t keep it from coming back this year. But yes, since Tenacity is not a fertilizer you can apply it after applying your Lesco. Your only real option to control it selectively is using Tenacity. It’ll take some persistence though. You’ll want to spray it when it is actively growing (like the rest of your lawn) and you want to make sure you mow low so the spray actually hits the blades of the creeping bentgrass. Once you knock it back and it turns brown (might take 3 applications), it’s usually a good idea to use a rake and pull out the dead grass. I prefer to use a metal dethatching rake that you can get at home depot or lowes. I have some in my lawn but I keep on top of it by spraying when it gets out of control. Also, in general I mow on the high side. The rest of the grass grows taller than the bentgrass and helps hade it out which it doesn’t like.
Hi guys, I like your site. Newby lawn homeowner looking to get my centipede grass in SC. growing great. I missed out on early pre emergent treatment. I’m almost ready to fertilize, is it too late for P. E.?
Hi Dave! I would definitely still put the Pre emergent down. Crabgrass and other annual weeds will continue to germinate until soil temps get into the 80’s. Just be ready with a liquid, lawn safe weed killer for any weeds that do pop up and you should be good to go.
My soul temperature is around 50° here in North Carolina but my grass is coming up. Looks like it’s in clumps. What do I do about this?
Hi Chris? What grass type do you have in North Carolina? Is it warm season grass or cool season grass? Feel free to take some pictures of the clumps and email me at mark@plantforsuccess.com. I’ll see if I can identify what’s going on.