I googled this because I was interested too and was alarmed to come up with the following:

http://eartheasy.com/blog/2010/06/6-reasons-to-avoid-using-%E2%80%9Cweed-%E2%80%98n-feed%E2%80%9D-on-your-lawn/

Organic care is desirable but our back lawn got thoroughly infested with buttercups while I was unwell last year and needs more drastic action than regular care. Hope you don't mind me muscling in on your question.

First, let me say that if you intend to weed'n feed your lawn now, whatever product you're using, don't, it's too late in the season. Second, I'm a bit puzzled as to why you think its so expensive - you only need one application of a feed and weed (if you must, but feed on its own is fine) in Spring - summer feeding might be necessary if the lawn looks very pale and weak, in which case you could use a water soluble feed (such as Doff or Qualcast liquid feed) but otherwise, its just that one application. Most weedkillers in lawn combined treatments are largely ineffective anyway - the best solution to use for weeds in a lawn is a separate, watered on treatment such as Verdone Extra, which is far more effective, and can be used to treat individual patches of weeds rather than broadcasting over the entire lawn. There are special Autumn weed'n feed formulations you can use in September, but unless your lawn hasn't been fed all summer and is looking pretty bad, its not necessary.

Note also that granular feeds are active for longer - they're usually designed to break down slowly over six weeks, whereas liquid feeds give an instant hit and are done, so probably best to use a granular mix in spring, then a summer liquid feed if necessary, and Verdone for weedkilling.

Would you use verdone at this time of year? (And patches of weeds are pretty even all over my poor lawn... does anybody want any creeping buttercups)

Verdone can be used anytime during the growing season. I find this product the best and most cost effective when dealing with weeds. One application each year is usually enough to keep your lawn weed free but the odd weed that shows itself can be spot treated.

Agree with Myron, absolutely.

Its a bit overwhelming to think of watering the whole area with a watering can - better take it a few cans at a time over the season! It did deal with some celandines in the spring - the grass suffered too but recovered quite quickly.

It's not that overwhelming Stera. I found that the rate of application needed meant that I needed to walk just slightly slower than usual, albeit backwards. So a slow walk across the lawn swinging the watering can left to right will take minutes. You can even swing the can right to left if you prefer ;O)

I guess it depends on how large your lawn is, and how large a can you're carrying...