This may be the most common question I receive about spinach production: What are the little white spheres that I’m seeing on the leaves? They rub off! I like this question, because it’s one for which I have an answer. These are not spores, insects, or eggs, as many people believe. They are trichomes. Trichomes are hair-like outgrowths from the epidermis of the leaf, and many plants (including spinach) produce them. Trichomes come in all sorts of shapes and sizes, and have different purposes. In the case of spinach, if you look closely with a microscope, you can see that there is a little hair that comes from the leaf surface, and a big glob at the end. An interesting piece of trivia: cotton fibers are actually trichomes produced on the seed of the cotton plant, Gossypium hirsutum.
Spinach trichomes have not been widely studied, but some varieties have more trichomes than others. The trichomes are usually more obvious on the smaller, not-yet-expanded, leaves, and I wonder whether they may be more prevalent on cold-grown or stressed spinach (but I can’t find research that has shown this). Regardless, the upshot is this: they are not harmful – they are just part of the leaf.