Mae 'Cennin Cymru' fel arfer yn cael eu plannu o ddiwedd Chwefror hyd at fis Mai ac yn cael eu cynaeafu o fis Awst tan Ebrill/Mai, gyda rhai cnydau'n aros yn y ddaear am hyd at 12 mis.  Gellir gadael y cennin yn y ddaear heb effeithio ar eu hansawdd, gan arwain at aeddfedu arafach a rhoi mwy o amser i'r blas pupur a'r arogl menyn ddatblygu'n llawn.
‘Welsh Leeks’ are normally planted from late February through to May and harvested from August through until April/May, with some crops remaining in the ground for up to 12 months. The leeks can be left in the ground without affecting their quality, leading to slower maturation providing more time for the peppery flavour and buttery aroma to fully develop.