I love these questions.

Aerate: never*
Crabgrass prevention: should be never but...when the forsythia are in bloom in YOUR neighborhood.**
Fill in low spots: When the grass is growing well and after you have mowed twice this season. That ensures you won't be smothering grass shoots.

*The reason I say never to aeration is that you can get a much better softening effect by spraying your soil with any clear shampoo at a rate of 3 ounces per 1,000 square feet. Follow up the shampoo with deep watering. Then deep water a week later. If the soil does not feel soft after deep irrigation (or rain), then repeat the shampoo. You cannot hurt the grass or soil with clear shampoo. Clear means something like baby shampoo and not something cloudy like Pert. There's more background to this suggestion. If you want more either morph or I can help you to understand why it works. It seems to work universally.

**If you are watering and mowing correctly, you should not have crab grass. Where do you live and what kind of grass do you have? What is your watering regimen? How often and how long?

I live in new York state about 30 miles north of the city. I'm new to owning a lawn but in the 3 years I've had the house the crab grass seems to be getting worse. I try and water once a week during summer but don't start at all until the weather heats up. I usually water pretty heavily (I think) MO ING the sprinkler location every 30 minutes to cover the full lawn. As for the type of grass I have no idea - my house is 60 years old and I'm the 4th owner so it's whatever I inherited.

The shampoo is interesting haven't heard that before - sure sounds better than the aeration plugs.

Thanks for the response :)

dchall- I remember reading that you said when looking for a shampoo, look for something that has a high surfactant because that is what makes shampooing effective.

Do you not recommend just buying a pure surfactant? Something like this: Surfactant

Or is that to much of a hassle versus the effectiveness?

dchall_san_antonio - I have never heard this shampooing technique before.
I live in zone 5a and have Kentucky bluegrass. I would
love more background on this technique. I am a recent lawn owner and I
have several bare patches and a dry lawn (mostly due to under
watering). I was considering aerating this
spring, but I would love more info as to why this isn't the way to go.
Thank you so much!

I never dreamed when I asked this question the answer would be so interesting. Thanks morpheuspa and dchall_san_antonio. When is the best time to do this treatment , I'm guessing by doing this before any top dressing I also have a better chance of getting a good interface between old and new soil?

Any time the soil isn't frozen and isn't going to be frozen within a few weeks is fine. For me here in PA, that's usually early April through late November. For you, near NYC, it's probably about the same. Your more northern locale is balanced by the ocean influence.

The interface between soils probably won't be impacted all that much. It won't increase mixing in and of itself, but encouraging with organics will attract worms. They'll mix and rotate soils for you.

So something like this would be a good choice?

Something like that, although...well, less expensive would actually be better. The glycerin in this case is useless (I performed that experiment several years ago with glycerin and water as a humectant, didn't work).

Lauramine oxide is a rather interesting amine oxide surfactant that's extremely effective but rather expensive. It's fine for skin (watch for sensitivity or dry scalp, of course, as that stuff is powerful), but not necessary for the soil.

Most other ingredients are at low enough percentages to be unimportant, although the bergamot, orange, Tangor (citris nobilis, a hybrid of orange and tangerine) and whatnot are in and of themselves powerful terpenes. I haven't done the research about those in soils so I'd tend to avoid them. They're fine on skin, but can cause sun sensitivity at amounts over 3%.

Really? Suave Clarifying or Suave apple scent. Why? Cheap, effective, and in the latter case I like the scent, which doesn't hang and disappears in a few minutes. At least I smell nice while doing it.

I never dreamed when I asked this question the answer would be so interesting.
That's why you pay the big money up front to play at this forum!

When I first heard of using shampoo I was skeptical. Since I tried it I have been promoting it. Everyone has aerated with a mechanical aerator (the bucking machine). The results from shampoo are much MUCH more impressive. I did mine back in 2011 or was it 2012? Anyway it's still soft after a rain or deep irrigation. My favorite is baby shampoo.

Test your sprinkler to see how much water you put down in 30 minutes. Put out some cat food or tuna cans and see how full they get. You're shooting for full cans to put an inch down. My oscillating sprinkler takes 8 hours but my neighbor's high flow in-ground system can fill the cans in 20 minutes. You need to know this so you can deep water the soil.

I caution against routine top dressing. The only time you need to add soil or sand to your lawn is to fill in holes, low spots, or to level it. I have pictures of lawns where 40 years of 1/4-inch top dressing has added up to 10 inches too much soil. Here's one of them. Note that they had to install a barrier to hold the soil back and keep it from washing onto the sidewalk.

There are lawns in the same neighborhood that have refurbished their lawns and hauled away all the top dressed soil. The next picture is from a different neighborhood, but it tells the story of what it should look like.

Any "clear" soap will do. I use whatever is under the sink. NEVER, however, use anything that is anti-bacterial. Look up Jerry Baker for his lawn recipes, most of which call for a bit of dishwashing soap and a beer. I did aerate when new to having a lawn and cracked a couple ribs. That's when I found Jerry. If we're expecting a big rain, I try to give the whole yard a quick spray of a weak soap solution. It really does keep the runoff down.

Crabgrass (and dandies) are forever popping up in my yard. I treat early and often and try a new chemical formulation almost every year. The cure for dandies is to dig each plant out--again, early and often. The secret to a better lawn (never perfect--know this now and you'll be happy you didn't move into an apartment condo) -- the secret is to walk around your yard every day and look at it. We call it 'surveying our domain', it takes a couple minutes, and makes a big diff. It's a lot easier to keep a nice lawn when you nip problems in the bud.

We have sink holes from a couple really big trees that were removed years and years ago. Eventually, all the roots might finally rot and collaps, and we might have filled the dips enough times so the yard might stay leveled off. I might be dead and gone by then, too. We fill the sinks every year, early and late.

I watched an episode of This Old House where Roger the landscape guy said you should top dress your lawn every year with a bit of good compost. I think that was more of a fertilizing suggestion than a yard leveling one. We top dress (with a mix of soil, leaf litter and sand) a section of our sliding yard (which slopes from back2front and side2side) every year in the spring, but wait until after the ground is no longer mushy from the snow. If your yard is flat and you don't have any water runoff problems, you may never need to do this. Still, be agressive with any and all holes and to do it as soon as you id them.

Good luck!

Baby shampoo is also great, and I recommend looking in your store's bulk section for the store brand. It's the same stuff. The surfactants aren't the same, but they do the same job, so don't worry if you don't see sodium laurel/laureth sulfate or ammonium laurel/laureth sulfate on the label. Those surfactants are more appropriate for an adult hide than a baby's.

SLS/SLES will be more effective by weight of surfactant, but baby shampoo is well within range.

As Zone7Patti noted, something like Dawn dishwashing liquid (or store brand) is also just fine, but don't ever use the antibacterial. Not because it'll kill too many bacteria at that dilution--it won't--but because we don't want to breed the next super bug by selecting for resistant bacteria. Besides, we work so hard to get the bacteria up to phenomenal numbers, any reduction and suppression of them is a bad thing. Antibacterials are generally ineffective on fungi and viruses as well, so use during a fungal outbreak won't do anything. Those few that are effective against fungi generally aren't found in washing liquid in any percentage that will actually do anything for your lawn.

Fun fact: aphids (and most other soft-bodied insects) can't stand soapy water. For sudden outbreaks not being handled by your hunter insects, 1 Tbsp per gallon of water will seriously reduce their numbers without harming the hunter insects or any other creature in your gardens.

Jerry Baker is an...interesting character. Some of those decoctions have some validity, some are merely old wives' tales with no real science behind them.

whats the best way to apply the shampoo ? I was thinking of using a hose end sprayer, i have a miracle gro pot that goes on my hose (one of these miracle gro sprayer), will that do the job ? Can i over shampoo ?

The Miracle Gro sprayer dilutes any liquid as it goes, so that's not the best idea (but it works well for any solid of low to modest solubility).

A hose end sprayer with a dial is best, set at somewhere around 1 oz per gallon plus or minus a lot depending on how much water volume you have, how fast you move, and so on. I tend to dilute the soap solution with water and double the setting to compensate, otherwise the soap is a little thick to get pulled up into the sprayer.

You can over-shampoo, but it's very, very difficult and you'll know you're doing it because you'll go through it extremely fast. I've regularly exceeded the 2-4 oz per thousand level by...well, a whole heck of a lot...and never had a problem.

If you do manage to dump an entire 32 ounce bottle of shampoo on 2,000 square feet or so (literally, that's what it would take to overdo this), irrigate well with at least 1 inch of water to dilute the shampoo and distribute it through the soil profile as fast as possible. That will alleviate any problems and you won't notice any issues from it.

Of course, if you do that, don't use soap again for about six months. On the up side, you absolutely won't need to do so.

Your Extension Service has opinions on everything and info on lots of problems in your area that you won't think of until it hits you. Remember to take advantage of your tax dollars at work!

I like hose end sprayers for most things to do with the lawn. They are pretty easy to use and cheap enough that I've got several and don't have to be concerned about a goofy reaction between chemicals. I use low concentrations of everything and repeat applications about once a month. I started doing this a few years ago after a particular dry summer where I spent a lot of water on the lawn. It took a little longer when I just started, but most of that extra time was spent finding just the right easy-access spot for the equipment.
I put half a teaspoon of soap in whatever I'm spraying from the hose. I use pressure sprayers for roundup and for deer deterant (stuff I want to stay on whatever I want it on). I also always use unscented soap--well, actually I use a not-soap (BasicH from Shaklee). Jerry Baker calls for lemon dishwashing soap in some of his yard formulas, but I don't like the smell of things out there that don't grow in my yard.

I didn't think I had anymore to say on this until I read this... "I watched an episode of This Old House where Roger the landscape guy
said you should top dress your lawn every year with a bit of good
compost."
Compost is the most expensive thing most people can put on their lawn. The application rate for compost is 1 cubic yard per 1,000 square feet. My yard is 2,000 square feet. Compost costs $35 per cubic yard with another $60 for delivery. So the cost is $65 per 1,000 square feet for compost. I can apply organic fertilizer for $4 per 1,000 square feet. That won't break my back, goes much faster, and works about 10x better than compost for improving every aspect of the lawn and soil. I can apply organic fertilizer 15 times before I get to the cost of compost. Don't waste your time or money.

Amen, dchall! We generate about a yard of compost and never have enough for the flower beds. TOH does a lot of things that require $$$ and tv magic.