ed ▁growth ▁and ▁er os ion . ▁Pl ants , ▁usually ▁obtained ▁from ▁northern ▁nur series , ▁are ▁plant ed ▁through ▁holes ▁p unch ed ▁in ▁this ▁covering , ▁and ▁ir rig ation ▁tub ing ▁is ▁run ▁under ne ath . ▁R unn ers ▁are ▁removed ▁from ▁the ▁plants ▁as ▁they ▁appear , ▁in ▁order ▁to ▁encou rage ▁the ▁plants ▁to ▁put ▁most ▁of ▁their ▁energy ▁into ▁fruit ▁development . ▁At ▁the ▁end ▁of ▁the ▁har vest ▁season , ▁the ▁pl astic ▁is ▁removed ▁and ▁the ▁plants ▁are ▁p low ed ▁into ▁the ▁ground . ▁Because ▁st raw berry ▁plants ▁more ▁than ▁a ▁year ▁or ▁two ▁old ▁begin ▁to ▁decl ine ▁in ▁product ivity ▁and ▁fruit ▁quality , ▁this ▁system ▁of ▁replacing ▁the ▁plants ▁each ▁year ▁allows ▁for ▁improved ▁yields ▁and ▁dens er ▁plant ings . ▁However , ▁because ▁it ▁requires ▁a ▁longer ▁growing ▁season ▁to ▁allow ▁for ▁establishment ▁of ▁the ▁plants ▁each ▁year , ▁and ▁because ▁of ▁the ▁increased ▁costs ▁in ▁terms ▁of ▁forming ▁and ▁covering ▁the ▁m ounds ▁and ▁purch asing ▁plants ▁each ▁year , ▁it ▁is ▁not ▁always ▁practical ▁in ▁all ▁areas . ▁ ▁The ▁other ▁major ▁method , ▁which ▁uses ▁the ▁same ▁plants ▁from ▁year ▁to ▁year ▁growing ▁in ▁rows ▁or ▁on ▁m ounds , ▁is ▁most ▁common ▁in ▁col der ▁clim ates . ▁It ▁has ▁lower ▁invest ment ▁costs , ▁and ▁lower ▁overall ▁maintenance ▁requirements . ▁Y ield s ▁are ▁typically ▁lower ▁than ▁in ▁pl ast icult ure . ▁ ▁Another ▁method ▁uses ▁a ▁comp ost ▁so ck