# Soil Temps/Pre Emergent/Scalping/Dethatching



## Wes (Feb 15, 2017)

I decided I would try to put together an actual plan for 2018 and in the process I stumbled down a rabbit hole. I'm going to be the first to admit that this is lengthy and very 101, but felt that what I found might be good for someone who is new to all of this.

My initial plan started something like this:

Apply pre-emergent
Wait for Bermudagrass to begin to show life
Scalp using rotary mower with bag
Scalp using reel mower until on lowest setting
Dethatch using the Vonhaus 2 in 1 Dethatcher & Aerator
Vacuum everything up

Now some of you may be thinking, "Wes, if you use pre-emergent before the Vonhaus you are going to tear up the pre-emergent barrier that you just applied." This occurred to me as well, and made me rethink the order of things. If this is true, I should go through the whole scalping/dethatching/vacuuming process and then apply pre-emergent.

I didn't really like this solution because I just felt like pre-emergent needs to go down before the Bermuda starts to green up. Also, I didn't get any pre-emergent down in the fall, and the last time I applied it was mid to late summer at 1/4 rate. Needless to say, I have weeds. Pre-emergent isn't going to help me with those now, but I need to get it down so I can start regaining some control. I also like the idea of applying quarterly as I feel it allows more flexibility because I don't have to worry so much about disturbing the barrier and not being able to apply more.

So I began thinking with the end in mind (this is where I fell down the rabbit hole): 

What is the proper order to do this?
How do I avoid this situation next year?
Can I apply pre-emergent quarterly and time it so that it coincides with the spring scalp?

I couldn't really answer these questions without going further down the hole. Ideally, I would want to dethatch right before needing to reapply pre-emergent, but this leads to two more questions:

When is the "right time" to apply pre-emergent?
When is the right time to scalp Bermuda?

I've always heard (ahem, or read) that the general rule of thumb is to apply pre-emergent when the forsythia begins to bloom. I live in the Dallas-Fort Worth area of TX and I've never even seen forsythia....at least I don't think I have. So in the past, I've used flowering trees as indication.

I noticed two days ago that a neighbor's peach tree has begun to blossom, but the Bradford Pears in the neighborhood have not. So although this might work as a general rule of thumb, it's not very precise. This rule of thumb also seems to be based on preventing crabgrass, which has never really been a problem for me. Instead, I find myself fighting Poa Annua, some perennial rye grass (I think it might be Poa Trivalis), dandelions, spurge, Dallisgrass, and sedge (in roughly that order from beginning of the growing season until the end).

So logic would tell me that different weed seeds germinate at different times of the year. Plants don't care about our calendar, they respond to environmental changes. Seed germination is based on soil temperature (among other things). So I started looking up the germination temperatures of the weeds that trouble me most. This is what I found:


Poa Annua germinates when soil temps fall below 70°F and continue to germinate throughout the winter. I read somewhere that they can germinate at temps down to 30°F, but cant seem to find where I read that.
Poa Tivalis can germinates well at lower temperatures of 40°F - 50°F
Dandelions germinate as low as 50°F and germinate more rapidly at 77°F
Dallisgrass germinates when soil temps are in the 60°F to 65°F range

This isn't meant to be a comprehensive list, but instead to show how seeds germinate at a range of temperatures. Okay, so that really brings me back to where I was - I need a pre-emergent barrier down all year long. So when is the best time to apply? In my case it would be right after I do the spring cleanup. I don't want to do it before the cleanup and then mess up the barrier when scalping and dethatching. That would be a complete waste... or would it?

So at this point, I'm committed to waiting to put the pre-emergent down until after I scalp/dethatch. The thought process is that if I'm applying pre-emergent at the quarterly rate a year from now I should be roughly on the right schedule to repeat the whole process again assuming the weather doesn't decide to do something completely irregular. So that more or less answers the questions about the appropriate order and avoiding this dilemma next year.

Now I just need to figure out when I can expect to start the scalping process. The Bermuda Bible: New Testament says I can expect to do this in the spring (Feb-Apr), but I decided to look for something more precise. Why? I don't know, because I'm nuts, or because I'm bored, or maybe it's just because I'm a TLF member and that's how we roll.

According to Richard L. Duble, from Texas A&M, "Green-up and recovery of bermudagrass begins when nighttime temperatures remain above 60° for several days in the spring and soil temperature reaches 65° at the 4-inch depth."

This now gives me a much better idea of when my new season will officially start. My meat thermometer just happens to have a 4" probe on it. So I'll be watching the weather for several nights above 60°F and then begin probing the soil.

My new plan looks more like this:

Watch for several nights above 60°F
When soil temps hit 65°F scalp/dethatch/vacuum
Apply pre-emergent at the quarterly rate
Wait for 50% green-up
Apply my first fertilizer application using a balanced fertilizer
Reapply nitrogen every 30 days

Was all this worth it? I don't know. I feel better about the new plan because I have a better understanding of the mechanics behind it. I also know that I still have three kids under the age of six and a wife who hates it when I spend half a day on the weekend doing yard work. I know I should throw some PGR into the mix, but I have roughly 20k of lawn and a cheap 1 gallon pump sprayer. I'm not quite ready to spend the extra money upgrading to the Spreader Mate and I feel that in the long run, I might regret buying something like the Chapin 20v backpack sprayer... but hey, it wouldn't surprise me if I was going down that hole this summer.


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## Colonel K0rn (Jul 4, 2017)

Welcome to TLF Wes, and here's your red pill. Sorry for the short answer, but I'm on mobile, so there might be typos.

Since you know that the PreM lasts for months, it's got to be down prior to the weed germination in order to be effective. The soil temps are relevant because they dictate when the weed seeds germinate, so you'll want to get the PreM down and in the ground prior to that happening. Think of it this way, the germination happens in the ground, and once the plant is rooted, it's going to start emerging from the soil. The PreM deters the rooting, so its more of a "PreRooting"; if anything, it's a misnomer.

You can divide your weeds into two categories: warm weather and cool weather weeds. Both have temperature parameters they follow for their germination criteria. You'll want to have the PreM in the ground prior to the germination of either category of weeds. I'm surprised you didn't mention crabgrass, which germinates around 55•.get your scalping and dethatching done prior to putting down the PreM, because you'll have more soil exposed and you need to get it into the soil (that's why you water it in). Breaking up the barrier AFTER it's down is what can allow seed germination, so the practice is to get it down after you scalp.

Most choose to do split apps because it's easier, but there is no hard and fast rule for timing. There is degradation with rainfall and irrigation, and two 6 month apps are what would be needed for year round coverage in a perfect world, with slight overlap. For a lot of homeowners, it's easier to do it that way.

I'm pretty sure the UT has an extension website that has the soil temps online that will allow you to see what they are in your area; they have that there for farmers to check so they can time crop planting. Use that as a guideline, but you got your thermometer as well. Same with the foliage around you; leaves falling, pollen counts, leaves changing color, etc. Learn those, and you'll have a good feel for the timing of when it's best to get a leg up on the weeds.


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## SGrabs33 (Feb 13, 2017)

IMO you can scalp when you are clear of extended periods of lows at or below freezing. Depending on how high and how thick your grass is now can limit the amount of sunlight that gets to your soil to bring up the temp. Scalping and dethatching could help decrease the time until your soil temps get into that 60-65 degree range.


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## tnlynch81 (Jun 29, 2017)

I live in McKinney and the optimal time for DFW to apply preM for summer weeds is going to be late February or early March depending on the severity of the winter. As soon as this rain stops is when I will be applying mine. I break mine up into 3 applications. One in late February or early March, a booster in late May or early June, and one final app to control winter weeds at the beginning of September. My lawn is 99% weed free after starting off as a salad bar. I still scalp when my lawn starts to green up with no negative effect. This will be my 3rd season following this plan and it has worked out very well for me.


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## Suaverc118 (Jul 28, 2017)

tnlynch81 said:


> I live in McKinney and the optimal time for DFW to apply preM for summer weeds is going to be late February or early March depending on the severity of the winter. As soon as this rain stops is when I will be applying mine. I break mine up into 3 applications. One in late February or early March, a booster in late May or early June, and one final app to control winter weeds at the beginning of September. My lawn is 99% weed free after starting off as a salad bar. I still scalp when my lawn starts to green up with no negative effect. This will be my 3rd season following this plan and it has worked out very well for me.


So after this stupid rain stops, you will apply your preM, wait a few days and scalp? 
Also, is it better to scalp first then apply preM, so your contact will be quicker??


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## tnlynch81 (Jun 29, 2017)

After this never ending rain stops I will apply preM, and then wait for green up. Could be days(doubt it by the looks of my lawn) or even weeks still depending on this good ole Texas weather. I get it down at this time to prevent as much weed germination as I can. My lawn is still completely dormant. :-(. The only green I see is the weeds in my neighbors lawn.

If you are in DFW I recommend listening and following Neil Sperry. He is a master gardener in Texas, and has his own radio show on Sundays. He gives lots of good tips about lawns as well as everything gardening. I have followed his recommendations closely and it has worked out quite well.


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## Redtenchu (Jan 28, 2017)

@Wes you are correct. Early spring time temperatures can vary so much I just begin when the weather isn't horrible and I have enough time to do everything!

I scalp/dethatch/scalp/Pre-E


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## Ware (Jan 28, 2017)

Redtenchu said:


> ...Early spring time temperatures can vary so much I just begin when the weather isn't horrible and I have enough time to do everything!
> 
> I scalp/dethatch/scalp/Pre-E


+1


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## Suaverc118 (Jul 28, 2017)

I dethatched last year, is it ok to do it every year or every few years? If it's ok, I may try to find one to rent, even though I'm not looking fwd to more work again like I did yesterday. Good Lawd!! If I'm lazy, I will skip it and use a rake to pull up the that and scalp again and re-apply my preM since I don't believe it fully soaked in the first time since I scalped too soon trying to beat this rain.


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## Spammage (Apr 30, 2017)

Ware said:


> Redtenchu said:
> 
> 
> > ...Early spring time temperatures can vary so much I just begin when the weather isn't horrible and I have enough time to do everything!
> ...


+2


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## Mightyquinn (Jan 31, 2017)

Suaverc118 said:


> I dethatched last year, is it ok to do it every year or every few years? If it's ok, I may try to find one to rent, even though I'm not looking fwd to more work again like I did yesterday. Good Lawd!! If I'm lazy, I will skip it and use a rake to pull up the that and scalp again and re-apply my preM since I don't believe it fully soaked in the first time since I scalped too soon trying to beat this rain.


I've been verticutting every Spring for the last 5 or 6 years. I feel like it removes a lot of the build up from the year before and gives me a better starting point.


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## Suaverc118 (Jul 28, 2017)

Mightyquinn said:


> Suaverc118 said:
> 
> 
> > I dethatched last year, is it ok to do it every year or every few years? If it's ok, I may try to find one to rent, even though I'm not looking fwd to more work again like I did yesterday. Good Lawd!! If I'm lazy, I will skip it and use a rake to pull up the that and scalp again and re-apply my preM since I don't believe it fully soaked in the first time since I scalped too soon trying to beat this rain.
> ...


Do you rent one and if so, which brand do you recommend? I borrowed one from someone on this thread. I'm just imagining how dusty and messy it will be again this year. Yowzers


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## Ware (Jan 28, 2017)

I like to scalp/verticut/scalp the Bermuda every spring because I don't have a fraise mower. :spiteful:

https://youtu.be/XTMuht1Rx7A


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## Mightyquinn (Jan 31, 2017)

Suaverc118 said:


> Mightyquinn said:
> 
> 
> > Suaverc118 said:
> ...


I bought an old JD one years ago and put new knife blades in it and it works great. Since I only use it once maybe twice a year, it was a good investment. Mine is so old that they don't even make any of the parts for it anymore  I think it's a John Deere 518 slit seeder. For a year or two, I would rent one from Home Depot and it seemed to get the job done pretty good.


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## Wes (Feb 15, 2017)

Colonel K0rn said:


> Welcome to TLF Wes, and here's your red pill. Sorry for the short answer, but I'm on mobile, so there might be typos.


Thanks...it's more of a welcome back for me. I disappeared sometime around April last year when things started growing. Between family, work, and the lawn I run out of time and my online presence seems to get pushed off the plate.



Colonel K0rn said:


> I'm pretty sure the UT has an extension website that has the soil temps online that will allow you to see what they are in your area; they have that there for farmers to check so they can time crop planting.


Thanks again. I didn't find the site you mentioned, but I found this one instead.



Suaverc118 said:


> I dethatched last year, is it ok to do it every year or every few years? If it's ok, I may try to find one to rent, even though I'm not looking fwd to more work again like I did yesterday. Good Lawd!! If I'm lazy, I will skip it and use a rake to pull up the that and scalp again and re-apply my preM since I don't believe it fully soaked in the first time since I scalped too soon trying to beat this rain.


Others have already chimed in that they do it annually, but I would say you could go one step further and do it twice a year if you don't mind the work. Let the turf tell you if it needs it. If you have spots that just aren't getting thick and you can see a layer of dead leaves on the soil, it wouldn't hurt.

Regarding the preM, the rain isn't a bad thing. You are supposed to water it in. Do you think it washed away?



Redtenchu said:


> @Wes you are correct. Early spring time temperatures can vary so much I just begin when the weather isn't horrible and I have enough time to do everything!
> 
> I scalp/dethatch/scalp/Pre-E


Thanks Red, I got the Vonhaus today and began to wonder if I should scalp first and then dethatch, or do it the other way around. I'll trust your experience.


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## Movingshrub (Jun 12, 2017)

tnlynch81 said:


> One in late February or early March, a booster in late May or early June, and one final app to control winter weeds at the beginning of September.


That's a pretty solid approach.

Regarding the verticutting concern, if the lawn needs it, I think that concerns exist independent of the pre-em timing. With that being said, everything I've read says the order doesnt matter.


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## Suaverc118 (Jul 28, 2017)

@@Wes , I mowed it like 3 days later and didn't get 1/2" of rain, and assumed we did because it drizzled for 2 days and even after I sprayed the preM. So that was my concern


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## Ware (Jan 28, 2017)

Suaverc118 said:


> ...and re-apply my preM since I don't believe it fully soaked in the first time since I scalped too soon trying to beat this rain.


Because you applied it at half the annual max, I wouldn't re-apply now. I would just sit tight and re-evaluate in 2-3 months.


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## Suaverc118 (Jul 28, 2017)

Ware said:


> Suaverc118 said:
> 
> 
> > ...and re-apply my preM since I don't believe it fully soaked in the first time since I scalped too soon trying to beat this rain.
> ...


Thanks @Ware !


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