Here is a list of things you might have been doing wrong:

1. Watering daily instead of weekly. Crabgrass needs continual moisture for a couple days. Of course this year you might have had Mother Nature helping you keep it moist! Normally you should be watering monthly in the cool months and gradually increase to weekly in the heat of summer.

2. Mowing too short. Tall grass helps shade out any weed seedlings to make it harder for them to take root. Unfortunately with crabgrass it is a sod forming type grass that spreads faster than other grasses. KBG should be mowed down to 3 inches for the best density and appearance.

3. Not getting full germination of the KBG last fall. It is very typical when rye and KBG are mixed that you stop caring for the new seed LOOOOONG before you get ANY KBG sprouting. Rye shoots out of the ground in a few days. KBG takes 3 weeks or longer of continual moisture (3-4x per day for 10 minutes each). Usually people see the rye and think that all the grass has come in and stop the frequent watering. Also the preem you applied was probably too late and the crabgrass had already sprouted.

Are you sure you needed lime and are you sure you used the lime specific to your needs? Only way to know is with a soil test?

Where do you go from here? Do you have any Kentucky bluegrass at all? KBG will be be your salvation. I would reseed this year following the same process but this time leave out the rye. KBG is also a sod forming grass. Once it becomes established it is rare that crabgrass can penetrate it. I have seen reports here on this forum where people say the neighbor's crabgrass comes right up to the edge of the property line and stops. When should you do the seeding? As soon as the summer heat breaks. Watch the evening temps. When they start to cool off is the time. Use the dethatcher to get any living crabgrass out, blow or rake all that away, and seed. You can leave out the aeration. That it a time consuming step that does no thing toward making the grass seed germinate. If you have hard soil that can be dealt with in other ways.

As for fertilizer, the fall is the time to apply 2/3 to 3/4 of the annual nitrogen requirement. However, that really pertains to chemical fertilizers. If you want to get the fastest and best bang for your fertilizer buck, take this opportunity to use organic fertilizer. You need quick response to this grass shortage and, even though organic fertilizers are known for being 'slow acting,' it will be fast because you can apply it every week (if you want) without any fear of harming the grass. Milorganite is a very popular brand of fertilizer and is going on sale everywhere for under $10 per bag. Personally I like to use ground grains like alfalfa, soybean meal, and corn gluten meal (too expensive this year). You can get these in plain brown bags at the feed store. Application rate for speedy results is going to be about 20-30 pounds per 1,000 square feet applied at least monthly. You can apply it the same day you seed or any day before or after. The water you will be applying for the seeding will be fine for the organic ferts.

Thank you so much for your response; it is so helpful. I can't tell you how much I appreciate it. I have a few follow-up questions. You mentioned in your post that there are other ways to deal with hard soil than aerating. I'm curious to find out about those other ways. We live in the Poconos and have very rocky hard soil so are there things we can do to improve it? We are going to take your advice and reseed with KBG and we will probably go with the milorganite. You mention that this fertilizer should be applied at least monthly, but for how many months. For example if we reseed in September and then fertilize directly before reseeding then for how many months after that do we continue to fertilize with the milorganite....until Winter? Again, thank you so much for all of your help.

Assuming you used a pre-emergent you got mixed with fertilizer from a box store, it likely wore off within 3 months. The makers of dithiopyr and pendi market their products as lasting longer, but there are many reports of crabgrass appearing in August, when they were put down in April/May.

The main reason you have so much crabgrass this year is because you had so much last year. Reseeding the lawn did not remove any of the crabgrass seed, and that is at least partly what is germinating now.

I live in western PA, and we have rocky/clay soil here, but it isn't "hard" unless its compacted. Soil compaction is a major problem that will keep your lawn from being hardy and will let crabgrass (and certain other weeds) take over, no matter what else you do. You should have tilled the soil before reseeding last year, assuming your soil was compacted; aeration alone doesn't cut it if the soil is heavily compacted. If the grass was growing well before the crab came, you can try to salvage this year by reseeding as soon as the crab dies in cooler weather; it sounds like you have too much to remove by hand. A picture would help decide that.

A dense, healthy KBG lawn is the best defense against crab, but it isn't perfect. You should use a pre-emergent in the spring, before crab germinates, then again two months later, to get protection through the summer.

Thanks. I guess I was throwing around the term "compacted" and not fully understanding its meaning. How do I tell if my soil is compacted? I would rather not till if we can avoid it; dethaching would be my preference. We just bought our house almost 2 years ago so this is just our second summer here, but it looked like previous owners had a beautiful thriving lawn until we took it over simply because we had no clue how to maintain it so I'm thinking that perhaps although we have rocky/clay soil we may not have compacted soil? I will post a pic of our lawn tonight.

Dethatching doesn't really help soil compaction. Core aerating will help, but tilling is best, if its really needed.

If the lawn was great when you moved in, its hard to believe compaction is the problem, because compaction doesn't just appear out of the blue.

At the same time, I don't know what would cause a lawn to go from beautiful to weedy in a single season. It usually takes a couple years of total neglect for a lawn to go to pot.

Are you sure you didn't just see the lawn in a weed-free state before you bought it, like in February/March?

Here's a picture of our lawn. I'll try to give an accurate history. We saw the house first in June 2009 and it was weed-free. It's worth mentioning that the summer of 2009 was an extremely wet one in PA however. We saw the house again in October 2009 and purchased it and moved into it in November 2009. The grass was weed-free and beautiful at that point as well. Our first summer living in the house was 2010. Being first time home buyers we really didn't know how to maintain a lawn. I fertilized with Scott's weed n feed in April 2010 and then again thinking more is better my husband fertilized in June with the same stuff. Then that summer turned out to be horribly hot and dry as a bone. By July our grass looked like a wasteland and was literally burned. We didn't water it and then the crabgrass came and it really took over. Then we did some research and decided to reseed in mid August. We dethached, aerated, limed, fertilized and reseeded with rye and KBG. The fertilizer was a good one recommended by a local feed store; not Scotts. And that's the history. Now, we thought our problems would be over this summer and again we're sort of back where we were last year :(

Here is a link that might be useful: {{gwi:113473}}

Compaction is a misunderstood term. Compaction occurs when all the air is driven out of the soil. The number of ways you can do that are very limited. One example is when cattle move about in a rain slogged pasture. When the pasture is wet enough their hooves sink in. Repeated plunging like that drives out the air. When the soil dries out, it is extremely hard and will not grow anything. Cattle producers usually have a sacrificial pasture where they put the livestock during a storm. Other than that, it is usually vehicles sinking into the soil that cause compaction. Over the centuries, rain can cause compaction. In Texas it is called caprock.

What you have is hard soil, not compacted soil. Rototilling is not the solution to that. Rototilling fluffs the soil, destroys the capillary structure, stirs up weed seeds, and removes the microbes from their preferred stratum in the soil to another one. It can take 3 years for all that to recover. Furthermore when you rototill, the underlying surface of the soil is uneven leading to a bumpy surface when the fluffy soil settles.

You can tell if your soil is unusually hard by walking on it after you irrigate. If, after an inch of water is applied, you walk on it and it does not feel soft under foot, then it is hard. You can soften it with baby shampoo. I usually mix the baby shampoo with molasses and apply from a hose end sprayer like the Ortho dial sprayer. I mix them 50/50 and stir the molasses to break up any clumps. I set the dial for 6 ounces per gallon and spray right before irrigating. The irrigation will further dilute it and carry it down into the soil. The soap will break the surface tension of the water and allow it to soak in deeper into the soil. The molasses helps water to stick to the soil and feeds the bacteria in the soil. Spray this every other week for three cycles and you should really notice the soil becoming soft after watering. It should last like that for a good long time unless you allow the soil to dry out too much. I always water monthly in the winter to keep the soil microbes happy. Of course I live pretty far south, so I can do that.

The fact that you had crabgrass last year is certainly a factor in getting it again this year, but the deciding factors were watering and thin coverage. You can have a lot of crabgrass seed in the lawn but never get it established if the seed never gets wet long enough to germinate.

I would make the last application of any fertilizer on or about Thanksgiving. If you want to use Milorganite, fine. Many people use a high N fertilizer like urea as a winterizer.

Ok, thanks. I will try the baby shampoo and molasses. So, is it ok to use just the milorganite as a fertilizer 4 times per year? Also, you still think we need to dethach to get rid of the existing weeds and scratch the surface of the soil to prepare for reseeding with KBG, right?

There are some who have used Milorganite 4 times per month throughout the growing season. 4x per season is fine.

Yes dethatching and scratching the very top of the surface is fine. The dethatcher should be adjustable to do that all in one pass.

Hi Moshie,
Just wanted to let you know I signed up for gardenweb because of this post. I live in the Poconos as well and am overwhelmed with crabgrass and terrible soil. Doesn't help when you live on the edge of the woods lol.

This post was edited by nepatitan on Sat, Aug 10, 13 at 15:44

"There are some who have used Milorganite 4 times per month throughout the growing season. 4x per season is fine. "

David, you really know people that would do such things?