Below is a list of common plants and botanicals that you can gather / buy / forage for and save up for dyeing. It's best to let these items dry out completely, then store them in a jar. If you are finding juicy berries like elder berries, it's best to dye them fresh, or save them in a plastic bag in the freezer until you are ready to use them. With flowers, I lay them out on a tray to dry, then store them at room tempurature out of direct sunlight and they will keep for years.
SNAPDRAGONS
HIBISCUS
PRIVET BERRIES
ALFALFA FLOWERS
ONION SKINS
TURMERIC
DOCK SEEDS
MULLEIN
IRIS
YELLOW SWEET CLOVER
BLACK EYED SUSANS
HOLLYHOCKS
RED ROSES
COREOPSIS
COSMOS
MORNING GLORIES
MARIGOLDS
ELDER BERRIES
BUCKTHORN BERRIES
SCABIOSA
DANDILIONS
BLACK TEA