What Is That Fuzzy Hair On Your Tomato Plant?

If you successfully grow, let's say, Roma tomatoes every year, you'll be hard-pressed not to have noticed something a little odd about them. The stems, and sometimes the leaves and even the fruit are covered with an abundance of fuzz. In fact, the same goes for your cherry tomatoes and those enormous beefsteaks. Sure, the hair cover is denser in some varieties than others, but it is always present to some degree. What we mistake for a luxurious coat of fur is, in fact, a collection of epidermal (or skin layer) growths called trichomes. These super fine hair-like structures might seem purposeless, but they serve as a vital natural defense against predation and environmental stressors.

Tomatoes (aka lycopersicon esculentum) are in the family Solanaceae, also known as the nightshade family. The grouping includes other delicious vegetables — think eggplant and potatoes — and some highly poisonous plants, like belladonna (a deadly nightshade). One thing nightshades — and a ton of other plant families — have in common is an abundance of trichomes. Tomatoes, for example, have anywhere between five and eight types across two categories: glandular and non-glandular. Together, they protect the plant against insect predation (the hairs secrete a sticky toxin that traps or poisons bugs), sun and frost damage, and moisture loss. As many a seed-saving gardener has discovered, even the seeds are fuzzy!

Glandular trichomes appear to be the stars of the tomato show when it comes to pest resistance. Depending on the type, they secrete an array of biological and chemical weapons from built-in glands, including sesquiterpenes, methylketones, acylsugars, jasmonic acid, and monoterpenes. These do everything from producing unappealing smells and tasting bad to trapping insects like a carnivorous sundew (which, by the way, also uses trichomes as sensors). The latter is the result of calcium and cadmium oxalate, essential oils that smell characteristically "tomato-y" and make the leaves and stem sticky. It's that dark-colored resin you get on your hands when pruning your plants.

According to a 2011 Brazilian Academy of Sciences study, these tiny, chemical-secreting filaments improve tomato resistance against leafminers, and per a 2019 study published in Acta Scientiarum. Agronomy, they also protect against green peach aphids. In 2018, a Frontiers in Plant Science study demonstrated that greater trichrome density led to a decrease in mite populations. The tomato's glandular trichomes do their job so well that researchers around the world are studying them to make other plants, like potatoes, more pest-resistant. Non-glandular trichomes were once thought to simply be difficult for bugs to climb through and over, but 2016 research in the New Zealand Journal of Botany shows they also secrete helpful chemicals — just at a lower volume.

Trichomes are overwhelmingly positive, but there are a few downsides. A 2011 paper published in Applied and Environmental Microbiology found that trichomes help deadly salmonella bacteria colonize tomato fruit destined for human consumption. Sometimes, trichomes also provide protective cover for pests. In 2012, Dutch researchers, via Experimental and Applied Acarology, noted that the tiny tomato russet mite stays safe from predation between leaf trichomes.

What all this research boils down to is that those teeny hairs do (almost) nothing but good for your tomato-growing efforts. You want more of them! Look for cultivated and wild tomato crosses, as wild tomato varieties tend to have more hairs than their commonly farmed or gardened cousins. You can help your plants to grow healthy trichomes by watering regularly and providing consistent nutrients. In particular, a fertilizer containing calcium silicate may increase the number of trichomes on a tomato plant. If you want to harvest tomato seeds like a gardening expert, save them from plants with the best combination of hairiness and delicious or large fruit.

One thing you might have heard is that the hairs turn into roots. This is, in fact, a myth. Tomatoes do indeed have cells that can turn into roots when a plant is under stress, but these are called parenchyma cells and look like little nodules on the main trunk of a tomato plant. Occasionally, gardeners mistake common pests and diseases for tomato hair. Everything from powdery mildew to the potato aphid looks fuzzy once out of control.