Up at the allotment I've been sheet mulching as much as possible, despite having gone over the whole plot at least once already (and several beds more than once). The weeds are vicious, especially the grass. Sheet mulching in spring/summer basically gives my own transplants enough time to get a footing before the grass comes roaring back by autumn: now. While both beds seem just as weedy as each other here at the end of the season, as far as harvesting actual food there was a big difference; I was able to grow big plants and harvest food from sheet mulched beds this year, whereas plants in beds without the treatment were simply no match for the weeds.
However, sheet mulching in autumn and winter will knock back the weeds and grass for longer--possibly until next autumn, depending on how deep I'm able to make it. I guess spring/summer mulch might last longer if I were able to make it really deep too, but I don't have a lot of cardboard to hand--I'm bringing home small to medium sized boxes from work which will cover about 1x3 m per week (single layer). It's not thick rigid cardboard unfortunately and each box needs to be overlapped by about 15 cm; it's enough to exclude light and smother soft vegetation but breaks down fairly quickly. I will try to pile the stable bedding on as high as possible, but that's the extent of it: a thin-ish, piecemeal cardboard layer topped by straw and horse manure.
I will say though, the soil is much improved since I started back in 2018; it's full of worms and holds moisture really well. I've not needed to water anything at all except the newest transplants and containers this year. And the horsetails haven't really appeared at all--they covered the place last year. It's still just teeming with grass!
