How to reseed grass after killing weeds?

Question

My lawn is overrun by clover and all sorts of weeds. I have lawn grass spots here and there, but the majority is weeds.

I was going to spray with "Ortho Weed-B-Gon Max", then spread some top soil and reseed, but I'm not sure if that's the right course of action.

The soil is kind of rocky and I suspect probably weak.

I'm located in Maryland, USA. The area is about 200 sq. ft. and I have no idea what kind of grass it is.

1. What would you recommend for weed control? Is Ortho OK, or should I get RoundUp, or something else?
2. Do I spray only the weeds or the whole lawn?
3. How long do I have to wait after I spray to reseed?

Answer 1

If the "lawn" is more weed than grass, I would kill everything and start over. If you take that option, Ortho is the wrong product because it isn't supposed to kill grass.

A review on Amazon.com implies that the instructions say you can't use Ortho on a newly seeded lawn for 4 weeks, so it would be sensible to wait 4 weeks after using it before reseeding.

Glyphosate (Roundup) works by being absorbed through the foliage, and is neutralized by contact with soil. It will take a few days for the weeds to die - if they are growing slowly because of cold weather etc, they will take longer. By the time they are dead you can safely re-seed. Some people would say it is safe after 24 hours, but you then have the problem that you can't clean up the dead weeds without damaging your new seedbed.

Bear in mind that the existing soil may be full of weed seeds waiting to germinate as soon as they don't have any competition from the current crop of weeds. Turf is more expensive than seed, but it will give you a weed-free and "useable" lawn much quicker. The layer of turf will suppress germination of weed seeds in the soil below it.

If you are going to clear everything and add new topsoil, hiring or borrowing a flamethrower may be cheaper than using weedkiller, and you can reseed immediately.

Answer 2

Just to throw my 2 cents in on this old thread that someone may find like I did, don't forget to water the weed seeds. This is a hard lesson I learned converting an old field into wildflowers. An applications of glyphosate would kill the plants the spray touched, but those plants were sheltering seeds and seedlings under them, which took off once the competition was gone. We sprayed the new seedlings and killed them off. When it was all brown with no green we burned it all with propane, creating a beautiful black bed for our wildflower seeds. Big mistake. As soon as we started to water the wildflower seeds, the dormant weed seeds in the ground took off.

So here is what we learned, painfully. This is not a quick process. If it's an old field, expect this to take more than a year. Apply glyphosate as soon you can. Burn it to expose the soil to the sun if you can. Kill the next flush of weeds, and the flush after, that, and the flush after that. If you think you are ready to put your new seed down, water what you think is "weed free" for a couple weeks. You will be surprised. Kill that flush, and THEN sow your seeds. Do not disturb the ground during this process because you will expose old weed seeds to depths where they can sprout. This is not a quick process, this is a long term investment you will have to put work into.

Answer 3

I doubt this answer will be welcome, but it needs saying anyway! I don't advise you should follow the course of action you've proposed - it sounds as if you've got mostly weeds and a bit of grass left, which would mean removing what's there and replacing it.

I'm not sure where you are, and I know that even 200 sq feet is quite a space, but really, you should remove everything that's there, dig it over, getting out the roots of the clovers and any other pernicious weeds with deep roots, and any large rocks/stones, emend the soil if it needs it, walk all over it on your heels to get out soft spots, rake it up lightly to leave a fine tilth for the top inch or so, then either reseed or lay turf (sod if you're in USA).

If you simply kill the area with a weedkiller, wait 4-6 weeks (which is really the minimum time) and re seed, you're likely to have a lot of weed regrowth - no matter what the manufacturers may claim, weedkillers aren't always effective at first go, and don't work perfectly on everything anyway. Again, despite the claims, Round up does leave a residue in soil which may be taken up by growing plants, although less likely to affect grass seed spread after 4-6 weeks. Your comment that you think the soil beneath the grass is 'rocky and weak', if an accurate observation, means that, unless you correct the soil beneath, you'll end up with a similar lawn to the one you've got now, despite adding topsoil and seed. Topsoil brings its own disadvantages - unless you pay top dollar, its often full of weed seeds itself, so its worth checking that you're getting good stuff, not just any old unscreened motorway spoil.

If you do choose to use the weedkiller route, check the package before using - most will give guidelines on how soon you can seed or grow plants in the area after use, and available products differ from country to country. Even Round Up make products for use in the States which are not available in the UK.

Answer 4

This is a complex subject, soil management. I took a course for "master gardener" from the U of Oregon which was one of the better things I ever did. This then brings us face to face with soils and the problems of soils. First get a good soil test kit from a hardware store and find out what additives you will need. Then till in the additives to a depth of six or more inches and then retill and retill until the soil is loose and sort of fluffy. In clayish soils you may need to add in humus and sand. Till to a depth of at least six inches, then either disc or rake out. If rocky soil, rake out as much of the rock as possible larger than a golf ball. Remember rock is essential in soils but only the stuff no larger than a golf ball. Nemotodes actually eat rock I am told, but ever so slowly. Till in humus if you can, such as decayed grass clippings that have been put through a cement mixer or any other mixer to render them relatively dry and powdery. That and some sand especially if the soil is clayish. The result should be such that if you pick up a handful and squeeze it you should get a ball that tends to hold together. The big issue is mineralization, thus iron, powdered, may be needed and is sold in gardening stores. Best to buy a book on soil preparation and go from there. My purpose here is to make the reader take note that this is like everything else in life, you need to study up. Thanks for reading.

Answer 5

Forget about amending the soil, or using pesticides to kill weeds, Duane.

The best next step for you is to rent a 'sod cutter' from an equipment rental store. Easy peasy to use, cheap and it will cut out all of the soil and weed crowns like now. 2" deep...or 1 1/2 inches. These pieces of sod make valuable soil for plant beds. Just pile them up upside down then cover with 4 inches of soil. Don't send this stuff to the dump.

You need to focus on defining a beautiful edge to your lawn. That is what the eye sees, those edges and as long as your 'crop' is uniform that will look beautiful.

When you make a curve keep that radius going until you decide to change to an outside curve. The radius size doesn't matter as long as you keep it consistent until you change the direction of the curve. Use string, a stake, even a hose works well. Make a 6"X6" trench all along the edge of your lawn. Use a flat shovel. Throw the grass and soil up on your beds. Simply redo your edges in the spring with a shovel and/or use a string trimmer. I'd buy one of these, a Stihl. Always wear eye protection and watch where the debris and rocks fly.

After cutting the sod, grade and rake the newly exposed soil after cutting out the sod. Then roll with a water filled roller also cheap to rent! Fill in any depressions and then roll again. Do this again. That surface when firmed with be the surface of your crop of grass. There should be at least a 1 to 2% slope to carry the excess water off of your lawn and directed somewhere the water should go legally.

Next let's talk about WHY this happened to your lawn. You most certainly have cool season grasses. Always a mixture of species. Make dang sure that the label of lawn grass seed states zero weed seed.

I'd be more inclined to use sod rather than seed. Far better to discourage any weed seed germinating during this time.

The next few suggestions are the most important thing you need to remember so this doesn't happen again; never mow lower than 3"! 3 1/2inches is best. Always sharpened blades. Always changing directions with each mow. Bag your clippings and use them in your compost pile or dumped on top of weeds in the back of your plant beds. Make sure the grass is no shorter than 3" after mowing!

Next critical thing you need to learn is how to water. Never ever every day. Water deeply and do not water again until you see your footprints stay down in the grass.

Next would be fertilizing. Three to four times per season. I use Dr. Earth's Lawn Fertilizer designed for the period of the season; spring, early summer, summer and fall! Dr. Earth's stuff you would only need 3 applications per season.

The next critical thing you need to do once per year is aerating! Pulling plugs of sod and soil out of the lawn then allowing them to stay where they fall. This is another piece of equipment to easily rent. Share this expense with your neighbors and have an annual PARTY!

You should not have to deal with any other chemistry or equipment. Raise the deck on your mower and if your mower can't handle leaving 3" of top growth take it to your new buddies! your lawn equipment service place. They'll be able to retrofit the height of your deck.

Critical height of cool season grass is 3 inches. Any lower there is not enough photosynthetic factories to support the grass plant. Our cool season grass lawn species are genetically gifted with large and deep root systems. They need top growth to support these large plants!

Cool season grasses have to be watered deeply then the soil needs to be allowed to dry out. As the moisture is used and evaporated from the surface the roots grow deeper to reach the moisture deeper. 4 to 6" deep. Watering a little every day is the worst thing one can do for cool season grasses.

Water deeply (remember the time it took for whatever irrigation method you are using). Use a shovel, dig down to see the soil profile. Simply jab the shovel into the lawn and pull back exposing 4" of lawn bed, the soil. When you see water reaching down 4" beneath the surface that is the correct amount of time.

Do not water again until...you walk on your grass and that grass stays down showing your footprints clearly. Perfect time to water and water deeply again. You should be able to train your grass to use only 1" of water per week. And during times of drought? Your grass will always be green!

The proper amount of top growth is able to feed these large root systems via photosynthesis (this is where the fertilizer necessary as photosynthesis doesn't happen without NPK and a good dozen or so microchemicals,(not to forget CO2). We humans are responsible for all of this chemistry. Leaving clippings on the lawn is silly. There is nothing left of chemistry of old plants to pass on to the new grasses or new plants. If the clippings aren't decomposed quickly enough they become thatch which completely ruins a lawn.

I sure hope this helps. There are lots of other question answers about lawns on our site for those who want to understand and grow their lawns efficiently, save water, promote healthy grass crops that are able to resist insect damage and disease. Lawns aren't that expensive or tough to manage if you know the rules!