Late summer is a great time to collect the heads of marigold flowers, after they’ve passed their prime but before they’ve started setting seed. It takes a lot of flowers to dye 4-8 oz. of wool (a brown lunch bag full), and even more (a grocery bag full) for a pound of wool. Marigolds will reliably yield colors ranging from light yellow through yellow-orange to khaki or olive green. It is reasonably colorfast. For the best yellows, I rely on alum mordant in a brass kettle; for greens, alum in an iron kettle. Yellow would probably result from using a ceramic or plastic container in a microwave. Some sources say to soak the flowers for up to 4 weeks in water, but I’ve never found that to be necessary.
Basic dyeing process:
Simmered the flowers in 1 gallon of water for about 1/2 hour, then remove the plant material. Submerge the wetted out wool or yarn in the cooled dye, bring to just below boiling, and simmer the yarn for another 1/2 to 1 hour. Allow wool to cool in the dyepot, then remove, rinse in cool clear water, and dry out of direct sunlight.
Historically, the marigold of medieval times is the plant we know as calendula (Calendula officianalis). The flower most Americans put in their gardens is Tagetes, with some varieties coming to us via Africa, and others from Mexico, where they are called Flor de Muerto, representing pain and grief. For centuries it has been used in dyes, beverages, and food coloring, and medicinally it is believed effective in heart and eye ailments. They repel nematodes and some insects in the soil. Opinion is divided about whether the petals are edible or toxic.