What is an Exploding weed? A Exploding weed is called a bittercress (Cardamine hirsuta) It is an annual spring and winter pest. The plant springs from a basal rosette and bears 3 to 9 inch long stems. Tiny white flowers form at the ends of the stems and then turn into long seedpods. They rip open and explode and fling seeds out . A bittercress plant like cool and rich soil . They spread really fast and since they like cool temperature they decrease as temperatures go up. The plant has a long, deep taproot, which makes pulling them out manually ineffective. The bittercress blow up when you touch them and the reasoning for them is so that they can replant themselves in the garden.