Plug plants/Jiffy 7s

I have found that with those pots the performance differs from year to year, if it's a wet spring, which happens a lot here, the roots will go through the pot, but if reasonably dry the roots can't get through, then when thing return to normal which usually means it's raining, the roots don't go through simply because they have started circling, not sure how the square pots do as the ones I have used were round