Cluster tarweed (also known as mountain tarweed or madia glomerata) is a flowering annual that is part of the aster family. It sprouts natively throughout much of northern and western North America, growing in many habitats such as roadsides. The leaves are narrow and are covered in sticky hairs. The plant grows to be 12 to 24 inches tall. It has a heavy scent that is like tar, and clusters of yellow-green colored flowers.
Choose a planting site that is in the full sun. The soil can be on the dry side, as clustered tarweed prefers a dry, open habitat.
Plant seeds in the fall. Dig holes about an inch deep and space them 3-6 inches apart. Place one seed in each hole. Cover with soil. Add water.
Touch the soil often with your finger to determine whether it is moist. Add water when the soil seems dry to the touch. Do not overwater. The clustered tarweed is drought tolerant.
Expect blooms in the midsummer to early fall. Deadhead (remove dead blooms) if you don't want volunteer seedlings next season. You can also remove seedlings when they appear if desired.
Collect seeds for future plantings by allowing seed heads to dry on the plants. Remove them by hand and collect the seeds. Store in a plastic bag or envelope until it's time for planting in the fall.