I normally mulch all my beans but have always thought that putting grass clippings around brassicas would take nitrogen from the brassicas so I have never done it. But things are very dry here and I would like to keep the moisture in the soil.
Yes I do mulch my brassicas..but with grass clippings only little at the time..
you can always put sprinkling of BFB or some chicken pellets underneath that mulch, to prevent any nitrogen robbery if in doubt..brassicas don't mind... ;) and eventually your clippings will release it back to the plants..or if you carry on mulching with clippings it will keep the new layer from robbing..
If you do not use grass clipping what do you use to mulch your brassicas.