Some dyes in my garden: Japanese indigo, goldenrod, tansy, marigold, madder. These give me the primaries--blue from indigo, red from madder, and yellow from the others.
I grow Japanese indigo, Persicaria tinctoria, in my garden and use it for dyeing. It is a magical plant whose leaves give the primary colors with the manipulation of time, temperature, and pH. The blue is indigo, the source of the blue in blue jeans. The red is indirubin, which is anti-leukemic and is being studied for the treatment of other cancers. The yellow is kaempferol, also found in fruits and vegetables and is antioxidant, antiinflammatory, antimicrobial, antidiabetic, antiobesity, and anticancer. This is not to say we should eat the leaves, but we can wear their colors instead. In India the concept of ayurvastra suggests that the healthful aspects of natural dyes can be transferred from the skin to the bloodstream; there is no scientific evidence and no research being done to prove or disprove this. However, we can entertain the concept and wear our naturally dyed clothing simply hoping or full on believing that it's healing powers will be of benefit to our bodies.
The colors are not the brights of the color wheel on cotton, and take best on silk without any additional chemicals. The blue is robin's egg blue, the "red" is actually pink to magenta and mixes with blue to give lavender to purple. There is currently no known method to isolate the indirubin, there is always a little blue involved. Indirubin is rare as a dye. There are only 3 known methods for obtaining it, and I developed one of them.
The yellow is a light yellow unless some chemistry is used to isolate and concentrate it. I get a beautiful green from the combination of blue and yellow. The brighter colors can be achieved on silk, on cotton the pastel colors prevail.
I get clear bright yellows on both cotton and silk from goldenrod and tansy, and golden yellows from marigold.
Madder is the source of red dye. The roots are used, although the leaves and stems can give pink. It takes 3 years from the start of a patch to harvest enough good quality dye from the roots.
I gather walnuts from my walnut tree, and also forage locally available dye plants.
Occasionally I will have access to sawdust from instrument and furniture makers and the rare arborist or small lumber mill with a known dye wood.