The tall stalk that grows from the center of lettuce is a flower that will produce seeds. This is known as “bolting” and is an undesirable outcome when growing lettuce. Once a lettuce plant “bolts” the leaves become tough and bitter. Check with your local university extension or master gardening program to learn ideal growing conditions for lettuce to prevent bolting.
Broccoli will continue to produce edible heads if the growing conditions are ideal. Once the main head is harvested, side heads will grow on the plant. Again, check with your local gardening clubs or university extension office for the best results.