I was unable to access your photos.
The three most important things that contribute most to a healthy lawn are proper mowing, watering and fertilization.
Search dchall, he regularly posts a detailed watering advice.
Fertilize once around the beginning of September. One pound of N per 1000 sq feet of lawn (sorry I didn't do metric). If available use a fertilizer with some phosphorous and potasium content. Once you notice the grass has slowed or stopped growing (around sometime in November) apply anothe pound of N per 1000 sq feet. Use an uncoated urea. Apply another pound of slow release N at the beginning of June.
Starting next Spring, mow your lawn at 3-4 inches to help block out the weeds and improve root depth of the grass.
It is best to plant grass in the Fall. There is less competition from weeds as the weeds begin to die off and Fall planting gives the grass the whole Winter to develope enough root to survive Summer heat and droughts. You may want to plant poa pratensis (or a mix containg it) as it is a sturdy cold season grass and prolific spreader.
Next Spring and throughout the Summer use a liguid weed killer that is safe for cool season grasses to knock the weeds down and give the advantage to your lawn.

Hi,
thanks for the reply. The link is working perfectly on my computer, are you by any chance using Safari? It seems to have problems loading Photobucket.

I am surely going to check out dchall's posts.

When exactly do you suggest I overseed and should I apply your fertilizing tips immediately, or should I start next year?
Because I've read that you should apply a slow-release nitrogen fertilizer right after overseeding, and a fast-release fertilizer ~5 weeks later. So that would kinda clash with the fertilizng schedule you posted.

Here are the Barenbrug seed mixes that I'm considering:

Super Sport - suggested for filling bare spots, their most aggressive mix. But I'm worried that maintenance will be crazy, especially mowing, and that the lawn will look even uglier than now because I won't be able to keep up.
29,00% Lolium perenne
43,00% Poa pratensis
10,00% Festuca rubra commutata
18,00% Fastuca rubra rubra

Exclusor - their "premium" mix
30,00% Lolium perenne
20,00% Festuca rubra commutata
50% Festuca rubra trichophylla

Water Saver - little watering required
80,00% Festuca arundinacea
10,00% Lolium perenne
10,00% Poa pratensis

Which one would you suggest?

I am not a student of turf grass cultivars and their indivdual characteristics, so I avoid giving advice on them. I suggested using poa pratensis because it is a hardy cool season grass with very good spreading and repair ability and I have personal experience with it. Any grass, is going to need some maintenance to stay healthy and green. Even supplying minimally adequate fertilization and water needs is going to require at least weekly mowing most of the growing season. The least expensive route to a better looking lawn is to properly fertilize, water, and keep the turf mowed at the proper height. In addition, overseeding can fill in bare/thin spots and help choke out weeds, making a better looking lawn.
You can overseed once the hot days of Summer have ended (when night time temperatures are regulary in the 60's-in the U.S., that is now).. The slow release NPK balanced starter fertilizer used for seeding you refer to is fine for the September application that I suggested earlier and if you do overseed and apply a starter at that time, just skip my revommended September fertilizer application. There are others here who can give you suggestions that may help meet your goals and expectations..
For some reason, I'm having connection issues, so that seems to be the reason for my inability to access your photos. Now to call my internet provider, then I'll try again later.

I would start with simple watering, mowing, and fertilizer. There is no hope for getting the yard of the month award, but there is plenty of hope to get a nice green spot for the kids to play. If you wanted the backyard of the month then you would have to start with RoundUp or other glyphosate product.

Have you read about deep and infrequent watering? If so, are you willing to water deeply once a month and up to once a week if you need to? I have two homes. One has a sprinkler system which I do not use. At both houses I prefer to use hoses with oscillator sprinklers. The turbo oscillators give a much more even distribution of water. This is what they look like.

{{gwi:84706}}

Mulch mow at your mower's highest setting for now. Tall grass will be healthier than short grass and it will resist weeds better.

What fertilizers are available to you? I would assume you could find alfalfa pellets (rabbit food) in Poland. That makes a great organic fertilizer at 20 pounds per 1,000 square feet (10 kilos per 100 square meters). Any kind of animal feed is a good organic fertilizer as long as it is ground up first. Just throwing corn on the ground will give you a corn field. Grind it up and it's fertilizer.

If you want to overseed and you have full sun, then I would go with some Kentucky bluegrass. If you have shade or less than 5 hours of full sun, then go with fine fescue. You can always mix them.

Here's a new link in case the Photobucket link is not working: http://www.flickr.com/photos/50788319@N06/sets/72157635419567072/

Haha no, I'm definitely not trying to get the backyard of the month award! Again, my front yard is a different story, but I'll take care of it next year ;)

Deep and infrequent watering sounds great and it's something I can definitely manage. I've seen tons of turbo oscillators in my local store as well as online so I'll get one of those.

Alfalfa pellets are available online but they sell them in small packages. It would be much easier for me to just get a lawn fertilizer instead of animal food.
We have tons of choices here and they're all available online, plus overnight shipping is the standard method of shipping here (perks of living in a smaller country ;) so it's really convenient.

Temperatures have now dropped to 65-70 degrees Fahrenheit, there may be 75 degrees on hotter days. Do you think it's a good time to overseed now or should I wait until temperatures drop even more?

Now, as for the grass seed choice, I'm still not sure which mix I should go with...
I don't have full sun all day. The main area of my lawn is in sun a lot (I'd say around 5 hours or more) and it's dry and spotty now. But there are also areas which are in shade most of the day, and they're greener and thicker than the rest of the lawn.
By the way, if you check out my photos, there is one picture in which you can see the shaded areas and the areas that are in sun a lot.

Here are the mixes I considered - I'm posting them in English instead of Latin. They're offered by Barenbrug - it's a well-renowned European company, something like Scotts in the US.
I'd love a thick, dark-green lawn. I've seen a lot of those in Pennsylvania but I'm not sure if it's possible to get that color in my climate. Most lawns around here are pale-green and "wimpy", just like mine.

Super Sport - their aggressive, durable mix, seems like a good choice but I'm scared of the maintenance.
43,00% Kentucky Bluegrass
29,00% Perennial Ryegrass
18,00% Creeping red fescue (fine fescue)
10,00% Chewings fescue (fine fescue)

Exclusor - their "premium" mix, which supposedly looks really good.
50% Slender creeping red fescue (fine fescue)
30,00% Perennial Ryegrass
20,00% Chewings fescue (fine fescue)

Water Saver - little watering required
80,00% Tall fescue
10,00% Perennial Ryegrass
10,00% Kentucky Bluegrass

For animal feed you go to a feed store. Wherever they sell horse tack or other feed. It comes in 50-pound (20 kilo bags).

The Super Sport grass choice will instantly become 100% Kentucky bluegrass. The percentages are by weight and not the number of seeds in the bag. KBG is very light compared to the others. 10% KBG gives about 50/50 lawn. KBG grows well in full sun and will repair itself if damaged. KBG will turn brown in the winter.

Fine fescues will grow in shade. It remains green all winter but it will not repair itself if damaged. You would have to overseed in the fall to repair damaged spots.

Rye grows in full sun and will not repair itself either.

The Water Saver is a full sun grass. Not appropriate for shady areas.

Pale green and wimpy. You might consider sending a soil sample to Logan Labs in Ohio. For $20 you get the best soil test you can get at just about any price. That might give you some ideas as to why the lawns are pale and wimpy. Given that description, I would definitely dump some alfalfa pellets on it. Here is a picture of the alfalfa effect. It was posted here at GardenWeb in 2010 by mrmumbles. He tossed a handful on one spot in mid May. The picture was taken in mid June.

{{gwi:79339}}

You can see the improved color, density, and growth.

I thought you suggested alfalfa pellets in case I can't find nitrogen fertilizers, but wow, that looks amazing. I will call local stores and ask if they sell alfalfa pellets, I will surely find something. If not I'll just order online.

I'm pretty sure the lawns here are ugly and pale green simply because nobody takes care of them, and people plant whatever the cheapest universal seed mix is available. My neighbors mow their lawns once a month, maybe twice and that's literally it. No watering and no fertilizing. I used to do the same!
I have a friend who has an amazing lawn - but he hires a lawn service and he planted expensive seed.
The soil test sounds like a good idea but I wish I didn't have to send the samples halfway around the globe. I was hoping a pH test would do in my case.. It would save me a lot of time.

Barenbrug also offers a Universal mix, which is a mix of 9 different fescue, ryegrass and bluegrass seeds (seems excessive), and a Shadow Gazon mix, which doesn't withstand foot traffic well at all.
There are also other companies offering seed mixes, but Barenbrug is said to be the best.
That's why I chose those 3 mixes I listed above. If you think none of them will work, I will look into other brands.

Is 100% KBG a bad thing? I don't mind KBG turning brown in winter since the lawn will be covered in snow anyway, but I do worry about the maintenance.

As for the fine fescue Exclusor mix, I think I'd rather overseed every year instead of having to mow 3 times a week. But will this mix be aggressive enough to take over my current weed-infested lawn?

I really don't know. Which seed would you go with?

I know. That picture sells a lot of alfalfa pellets.

Absolutely nothing wrong with 100% Kentucky bluegrass lawns. In fact if I ever move somewhere where it's appropriate, that's what I'm going to have.

You should not have to mow KBG 3x per week. There might be a week or two in the early spring where it is leaping out of the ground faster than you can keep it mowed. But for the rest of the season it will only be once per week.

I would probably get the SuperSport and let the KBG dominate in the full sun. The other token fine fescues will eventually dominate if there isn't enough sun in places. Those places will need overseeding if it thins way out.

The KBG, if mowed high, should crowd out most new weeds. Currently established weeds might not leave voluntarily. For example your coarse bladed grassy weeds will make a KBG lawn look weedy. I would try to kill those before seeding. The fine bladed grasses will blend fine, but the coarse blades will not. Broadleaf plants (not grassy plants) can be sprayed out with a product containing 2,4-d. Here it comes as Weed-B-Gone.

Here is a picture of a "contractor grade" KBG lawn when the lawn is mowed high, watered deeply/infrequently, and the soil is highly tuned up and cared for with organic fertilizer.

{{gwi:103346}}

Contractor grade means it was the grass that came with the house. You can spend a lot more on the Elite KBG seed if you like. Usually the Elites are much deeper green - like a blue/green. But clearly you don't need to have an Elite to have a sensational lawn. This lawn is, I believe, in Eastern Pennsylvania. It is cared for by a lawn genius named morpheusPA.

Surely there is a good soil test facility in Europe. I'm thinking France only because some of the early pasture grass experts were from France. If you really want to help your soil you need to know about the salt balance and the micronutrients. At Logan Labs that test is $20. At almost all other labs it will cost $60 to $100 to get all that. Keep that in mind when shopping. You do not have to wait for return mail from Logan Labs. They email you the results.

Thanks dchall,
KBG it is, then. I was leaning towards it from the beginning anyway. The picture you posted looks super nice.

Weed killers containing 2,4-D aren't popular at all around here. I found one product containing it and it's not meant for home/lawn use.
There are a lot of fluroxypyr and MCPA based herbicides available though. They get good reviews so I guess they should work.

I found some local labs that do soil testing for farmers. I'll call them and ask if they will test my sample if I send it to them.

Now, to sum things up: I should kill as many weeds as possible first, and then overseed.
When do I start fertilizing with alfalfa pellets?
When do I start with deep and infrequent watering?
And finally, do I need to get my soil tested before overseeding, or can I do it after?

Thanks!

It can take years to fix a soil chemistry. Don't wait to overseed. Do it now.

Fertilize anytime with organic fertilizers. Unlike chemical fertilizers, you cannot hurt anything with organics. They are nothing but food. The critters eating the food are soil microbes. In turn they create plant food which produces the results that mrmumbles captured so well. This food recycling process has been going on for a billion years. You can use up to 50 kilos per 100 square meters before the problem becomes that you smothered the grass. Also you might detect a certain aroma from the decomposing organic fertilizer. That is short lived and due to your soil not having a sufficient population of microbes to decompose the food faster. The second and subsequent times you will not notice the smell. It is not a horrible smell by any means. It's just noticeable as not normal.

You should be watering about 3 cm, once per month this time of year. Here's a chart for you. It is based on daily high temperatures.

Above 35 degrees C ==> water 3 cm once per week
25 to 35 ==> once every 2 weeks
20 to 25 ==> once every 3 weeks
Less than 20 ==> once per month

Of course Mother Nature will help you out sometimes so you won't need to water the full amount every time. Your exact temps and amounts will vary with your soil, shade, clouds, rain, wind, humidity, grass type, grass length, and grass density. Rather than trying to quantifying all that, it is much easier to watch the grass and see when it turns dark and the blades fold together. Then water immediately. If the time period was not a full week (or whatever), then water longer next time. The objective is to let the surface of the soil dry completely before it gets wet again. Weed seeds need continually moist soil to germinate. When you let the soil dry out, then the weeds cannot germinate. Mother Nature will fight against you on this front.

Are you from the US? Are metric measurements better for you or are you converting back to inches, pounds and Fahrenheit?

Wow, thanks dchall, this is amazing amazing info! Things are really clearing up for me.

I hope I'm not being too much of a bother, but do you suggest I overseed literally now - in 2 days or so - or do I spray the weeds with a weed killer first (as you suggested in your previous post), and wait 2 or 3 weeks before overseeding?
Also, most overseeding guides suggest the use of a slow-release nitrogen fertilizer directly after overseeding. Do you suggest I completely avoid chemical fertilizers in every case, and substitute the slow-release fertilizer with alfalfa pellets too?
Sorry if I'm being annoying with my questions, it must look like I haven't even read what you'd previously written. Believe me - I have ;) I'm just trying to make sure I fully understand everything so I can get things right and I won't have to fix them later.

By the way, I finally found alfalfa pellets for 55PLN for 12kg ($17 for 27lbs). More expensive than in the US, but way cheaper than chemical fertilizers. It took a lot of searching!

And no, I'm not from the US - I'm from Poland. Metric is perfect, but imperial units are not an issue.

Thanks again dchall!

Your English is incredible!! I'm always amazed at people who can speak more than one language. For that reason my daughters also speak, read, and write Spanish. My oldest wants to teach American history in the Spanish language at the high school level.

Get started with the reseeding project now. Start with the herbicide now. Do it in order.

Thanks, I'm really flattered! Spanish seems like a beautiful language. My mom used to be an English teacher and she has always encouraged me and my siblings to learn languages (we also speak German and a bit of Italian). While studying wasn't always fun, the effort was definitely worth it. I'm sure your daughters think the same!

And many thanks for all the gardening tips! I'm getting to work as soon as the rainy days are over.

Tell your mother you're getting praise for your English from a Texan. She did a good job.