Any plant growing under rootbound conditions suffers a degree of lost potential roughly commensurate to how serious the congestion is. As the congestion increases, so do the congestion's limiting effects.
I've grown a LOT of grasses and various other monocots long term as companion plants to bonsai on display, and can say with absolute certainty that grasses and other monocots grown under conventional container culture are not exempt from the effects of tight roots. They are as affected by root congestion as both woody and herbaceous dicots.
Even if we were to allow that roots of monocots don't increase in diameter (I question that idea), we know with absolute certainty that they do multiply and fill containers the the degree access to resources is limited both by the increasing volume of roots and by the decrease in available oxygen. When I repot plantings of grasses or other monocots to relieve root congestion, It's typically because growth has nearly stopped or stopped altogether. After removing most of the roots from the bottom of the root/soil mass so the remaining root mass is about 1/2" thick, and repotting into fresh soil, the increase in growth rate, vitality, and the increase in stems is very conspicuous. The increase in growth rate, vitality, the plant's ability to defend itself, and typically - eye appeal, should not be seen as a growth spurt. In fact, it is a clear indication of how serious the limitations associated with the root congestion actually were. The plant could have and would have been enjoying the "new and improved" increase in growth and function all along had the plant been repotted at appropriate intervals rather than being left to suffer the effects of root congestion.
Al
