Field experiments were conducted at the Marfa Mawr field station of the University of Wales, Aberystwyth, over 2 years to study the effects of seeding density and row spacing on dry matter accumulation in linseed (Linum usitatissimum L.). Dry matter accumulation increased progressively in all the densities and row spacings with the age of the plants during both the years. However, during 1993 a reduction in dry matter was observed between 106 days after sowing (DAS) and maturity (138 DAS), but this did not happen during 1994. This reduction was considered to be the effect of lodging of the crop and leaf senescence. The lodging took place due to heavy showers of rain and high winds near maturity, and plants were not able to support the weight of capsules. The greater amount of total dry matter accumulated during 1993 compared to 1994 was related to climatic conditions (moist and relatively cool in 1993) on one hand and the total length of the crop life cycle on the other. A total of 391 mm of rain was received during the crop life cycle during 1993 while 229 mm of rain was recorded during 1994. A difference of 2 °C in mean temperature between 1993 and 1994 was also recorded.