Posted: 19/05/2015 at 13:47
Grass can be surprisingly difficult!
I haven't been trying to care for my lawn for long (at least, not with any real focus) but I have found some good advice here: http://www.lawnsmith.co.uk/
It will be a while before I find out if it works though!
First thing to think about would be what kind of fertiliser did you use and at what kind of concentration and did you water it in well - applying too much nitrate rich fertiliser without watering it down well can lead to a kind of chemical burn on the grass - if you have seen grass die where dogs pee on it, this is exactly the same effect. I wonder if that has happened in the middle of the photo because it looks worse than just a bit brown?
A lot of places just sell combined weed and feed stuff, but there are different lawn fertilisers for different times, it may be worth checking to see if there is something more suitable.
I scarified my lawn much more heavily than that a couple of months ago (really you could see a lot of bare soil!) it hasn't come back evenly yet but it is growing strongly and without moss (although plenty of weeds). I don't think you have anything to worry about, but you can still do some things to try and help it along.
Firstly if it isn't going to rain water it regularly - if it isn't draining reduce the amount you water it, but try to keep it well enough supplied. One tip is to make sure you water before midday to give it a chance to dry by evening because apparantly cold damp conditions in the lawn are good for disease to take hold. When it rains 24/7 like it seems to here at present I guess the lawn just has to take its chances, but when you can control the watering regime you might as well.
Another thing which is important is soil compaction, or rather de-compacting it. Aerating with a fork or a hollow tine aerator can be quite beneficial in loosening up the sub soil and giving the roots a chance to spread out and down (most plants need at least as much area for roots below ground as they cover above ground). That website does suggest that aerating once a year is a waste of time, it needs to be more regular (unless you have really loose/sandy soil) I guess I need to be thinking about doing mine again by now.... It seems that trying to fill the holes with sand or fertiliser is a waste of time, and filling holes on clay soil with sand will make it worse.
Overseeding - apparantly always worthwhile, although I think the birds got most of mine! do this after aerating and disturbing the soil a bit because the seed will need good soil contact to germinate (if you can rake the top layer of soil that seems to be good). It is recommended to lightly roll or trample the seed onto the soil - light roller means half filled or less water roller, you don't want a cricket pitch with good bounce and heavy rolling will undo the aerating. I would over-seed ASAP because you want the young grass to get light to grow and you don't want to be cutting the lawn again until it is well established....
You can overseed at about half the rate for a new lawn.
Grass seed needs warmth as well as water - right after I sowed mine it turned cold again and has never really warmed up properly
Top dressing - (applying soil/compost on top) may be useful if you are going to mix the seed in with it (ensuring soil contact!) and for filling shallow depressions, but otherwise seems to be something best left to the professionals managing grass for sports use and similar - getting the application rate right seems complex and it is going to be pretty heavy work!
It all seems like a lot of work for a weed that grows pretty well anywhere you don't want it, but refuses to grow nicely where you do!