Whenever we did a clear out of our deep litter sheds & sold off a shed's chickens we left the run area to its own devices .
It was only a matter of a few weeks before chickweed , grounsel sow thistle & fat hen etc came through & overtook the whole area inside the pen. Then by the new replacement chicks were about five inches tall , we'd let them out into the run area where over the nest several week they decimated everything yet again .
Dad never ever re seeded the pens as it takes six or more months or more for the new grass to get a decent root system and then the chickens would decimate it within days if the pen enclosure was less than 3 sq yards per chicken .
What dad , my mum and my big brothers did do was to move the pens to clean ground in early November and dig over the old pen area for the next years veg gardens and make a well staked down & supported wire tunnel out from the shed " POP hole " into the newly sited pen area .