Seeds of Asparagus officinalis cv. "Mary Washington 500 W" were sown in spring, 1974, and plants grown were transplanted at the density of 330 or 660 plants a-1 inside a plastic house, then crowns were covered with plastic tunnels for forcing during period of 90 days in winter. The treatment was started from either December or January. Spears were harvested when they reached to the height of 20 cm. Number and fresh weight of spears harvested increased with the rising of temperature and showed little difference among plots with the same plant density regardless the starting date of the treatment. Total amount of yield in plots with higher density showed about 1.6 times more than in lower one. Dry matter ratio in a spear showed to be high in a distal half, and the ratio decreased proportionally with the reduction of days required for spears to reach 20 cm long after sprouting on the soil surface. Firmness of pith of spear ranged from 3 to 8 dyne/cm2×105 and the most tender part was at 10-15 cm below the tip. This part coincides with the part at which spears are snapped. Firmness, which was measured by the penetration force test, tends to decrease with the increment of spear diameter, and the highest correlation between the firmness and the diameter was seen in the proximal side of the snapped part.