Questions on mowing and weed killing after overseeding

llo0dqleJune 24, 2013


I am a first time home owner and I just moved in end of May. The previous owners had a dog so the back lawn (which is pretty small - it's a half duplex) was full of dog spots - about 50%. It was also full of dandelions. It has a detached garage in the back and on the one side of the garage, the grass was pretty much dead and full of yellow straw like hay. The front lawn wasn't bad, but was a bit thin and had a few dog spots as well. So, I decided to overseed.

I didn't really know anything about lawns or grass before all this but I did quite a bit of reading and have learned quite a bit. I don't know what the existing grass was but if I had to guess, it's probably fine fescue. I mowed the grass as short as I could with my Yardworks 14 inch reel mower. I dethatched for hours with a dethatching rake. I pulled dandelions (as many as I could). I core aerated with a manual aerator I got from Home Depot. I put lime on the dog spots. I top dressed with Scotts enriched lawn soil (about 12 bags of it overall) covering about 1/4 inch of the topsoil. I spread Scotts Premium Sun and Shade mix with the Scotts hand spreader and finished off with Scotts starter fertilizer. I then ran my leaf rake upside down over the lawn to press the seeds into the soil. Finally, I watered the lawn.

I did all this about a week ago and have been faithfully watering twice daily to keep the soil moist. Now, the existing grass is pretty long (about 4-6 inches) and I think the seed is just starting to germinate. It's hard to tell because of the existing grass but the mix is PRG, Red Fescue (I think) and KBG. I think it's the PRG that's starting to sprout. Also, the dandelions are starting to grow tall and my front lawn is starting to have quite the population (I think partly due to my neighbor who neglects her lawn and has a million dandelions growing).

So, my first question is, when do I mow? I've googled and googled and googled and I'm getting different views. Some say wait as long as possible so as not to disturb the seedlings. Certain pro articles say keep mowing and keep it at 1.5 - 2 inches so the seedling are not in the shade of the tall existing grass. Some say, mow when the height of new grass is 2-3 inches. Now, if PRG germinates at 7-10 days, red fescue at 14-21 and KBG at 21-28...when the heck do I mow?? My other concern is that the existing grass is getting long and it might be depriving the seedlings of sunshine. But if I mow using my reel mower, I will be leaving long clippings which can smother the seedlings. If I rake them, I might be uprooting seedlings. If I borrow my dad's gas mower so I can bag the clippings - other articles/forum discussions say that it will suck up the seedlings. I'm so confused.

Also, regarding the dandelions..(I think all the weeds are dandelions, I don't think I saw crabgrass and I don't know what quack grass is or other weeds). Can I spot spray with Killex right now? Or do I have to wait until the new grass is established. Better yet, can I broadcast spray the Killex? If so, when can I do this? Killex supposedly doesn't affect the lawn but the label doesn't specify regarding new seedlings. Some articles vaguely say to wait 8-10 mowings before doing any weed control but I don't know if that applies to Killex per se.

It's day 8 since I overseeded and I am constantly thinking whether I should mow the lawn now or wait. If I wait, I'm wondering when I should do it.

Please help and thanks in advance.

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SouthCountryGuy Zone 4b-5 SE BC(Zone 4b-5 SE BC Canada)

I am by far not an expert grass guy but I can give you some insight into what I have learned after starting 3 large lawn areas under less than ideal conditions. It sounds like you have done a great job so far.

IMHO I would mow your grass will be 2 feet tall if you wait for it all to germinate and be 3" tall. Sure your going to crush/damage/kill some seedlings but how many are you going to lose if they are deprived of sunshine? Plus you will be stressing your existing grass by chopping too much off. The clippings, if anything, will help retain moisture for them. I try not to step on or roll over known seeded areas, sounds like this might be hard for you.

I agree with waiting 8-10 mowings to broadcast spray. I have killed seedlings by jumping the gun. I personally would wait till fall. You could spot spray and will only risk killing seedlings with the over spray or, thanks to a user here, use a small paint brush and paint each one.

I over seed my lawns every spring and fall. I broadcast spray with killex the day before I am going to seed. Watch home depot and the like in late fall. They usually blow out seeds and other gardening stuff at pennies on the dollar.

One thing that really helped me and my lawns was buying a soil test kit. I test my soil about 3 times a year (spring, mid summer, fall) to find out what it is lacking and buy fertilizer to balance it out. I didn't realize my soil was very alkaline and after dropping the PH my lawn is doing WAY better.

Good luck


    Bookmark   June 24, 2013 at 11:11PM
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Thanks for the response. How about if I trim the grass with my grass trimmer/edger? That way I don't roll over the seedlings with my mower and I can continue to maintain the height of the grass and not have the clippings so long that they weigh down the new grass. The only thing I was worried about is if grass trimmers don't cut as cleanly as a sharp mower blade. But given everything else, it may not be a bad option. What do you think?

I was just thinking of doing a soil test because I also read that sometimes when dandelions abound, it's because the soil is deficient in calcium or has a high calcium to phosphorus? ratio.. I'm not sure it's phosphorus but something..

When you broadcast with Killex, you seed the day after? I know it's safe but I was just wondering if it is still effective with killing the weeds because apparently it can take up to 3 weeks to completely kill the weeds..just wondering if you are cutting off the flow of the Killex into the root system by mowing right away the day after..

Thanks for the paint brush tip, I will probably do that and confirm my gf's claim that I am insane. But seriously, I will do it. lol

    Bookmark   June 24, 2013 at 11:26PM
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SouthCountryGuy Zone 4b-5 SE BC(Zone 4b-5 SE BC Canada)

I would just mow it. If one didn't pay attention to the germination times, like most people wouldn't, and followed the instructions on the bag mowing when the grass was 3" tall they would probably be just cutting PRG as the other may not have germinated yet. Grass is pretty tough and with time it will all fill in.

I couldn't tell you exactly the conditions weeds prefer although I think I remember reading that they like a more acidic soil.

I usually mow before spraying killex. I also don't drop my lawn mower down like I am "supposed" to before seeding. I haven't found it changes anything.

Yeah the wife thinks I am nuts with the paint brush in the flower beds. I go all out with the paintbrush and use round up. I also use round up saturated paper towels to wipe quack grass and other weeds. It is also in empty spray bottles from eye glass/lens cleaner as well as windex bottles. Yeahp...I could be committed.


    Bookmark   June 25, 2013 at 12:48AM
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Thanks for all your help. I emailed Scotts regarding Killex and this is what they said:

"You will be able to safely sod or plant seeds in the area two to three weeks after treating with Ortho Killex Ready-To-Spray. We also recommend that you heavily water the treated area once during that two-week period. Grass seed or new sod will be damaged or destroyed by a weed control. For that reason, we recommend waiting at least two weeks before replanting or sodding in a treated area. If applying after you have planted new grass seed, you will need to wait until you have mowed the new grass a total of 3 times.

Killex Ready-To-Spray can be used on Bentgrass, Buffalograss, Centipede, St. Augustine (do not use on the Floratam variety of St. Augustine), Bahiagrass. Bermudagrass, Bluegrass, Fescue (any variety), Ryegrass (annual and perennial), and Zoysia.

Do not use on Carpetgrass, Clover lawns, Dichondra lawns, Floratam (a variety of St. Augustine common in Florida)."

Thought it might help..

    Bookmark   June 26, 2013 at 7:26PM
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SouthCountryGuy Zone 4b-5 SE BC(Zone 4b-5 SE BC Canada)

Yeahp thanks. Confirms my errors in the past.


    Bookmark   June 26, 2013 at 7:47PM
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