Weeds are adapted to be opportunists. Annual weeds can grow on vacant land and compete with crop plants as they have the following characteristics:

• rapid growth
• short lifecycle
• produce large number of seeds
• long-term viability of seeds

Perennial weeds can also successfully compete with crop plants due to a different set of characteristics:

• storage organs - therefore the plant has food in all environmental conditions.
• vegetative reproduction - perennial weeds can reproduce using other methods in addition to seeds (sexual reproduction).