Strange Growths on Tomato Stems

Aerial roots on a tomato stem. Photo:

Question: Some of my tomato stems have strange bumps on them. I’m afraid they might be some sort of insect eggs or maybe mushrooms. Should I pull these plants? 

An Anxious Reader

Answer: No, just leave them alone.

What I see in your photo are just the beginnings of aerial roots, also called adventitious roots. They’re perfectly normal. Some tomato plants produce them readily, others not at all. Growing conditions seem to be a factor as well: they can actually grow considerably, to an inch or so (2–4 cm) long under high humidity.

Aerial roots are absolutely not harmful and you need do nothing about them. If they’re near the ground, you could even layer them, that is, cover them with soil, encouraging them to develop into full roots, thus giving your plants access to extra moisture and minerals. Also, you could take cuttings of stems with aerial roots and grow the new plants, although in all but the most tropical climates, that’s rather pointless, as the new plants won’t have time to produce fruit. 

Essentially, they’re a relic from the time tomatoes were wild lianas growing in tropical South America, a sort of back up strategy allowing them to reroot if they were damaged or knocked to the ground.

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

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