Bumpy Tomato Stems: Learn About White Growths On Tomato Plants

Bumpy White Growths On Tomato Plant Stems
tomato bumps
(Image credit: Gardening Know How, via Nikki Tilley)

Growing tomato plants definitely has its share of problems but for those of us who adore our fresh tomatoes, it’s all worth it. One fairly common problem of tomato plants is bumps on the tomato vines. These bumpy tomato stems may look sort of like tomato acne or may look more like white growths on the tomato plants. So, what does it mean if the tomato stem is covered with bumps? Read on to learn more.

What are White Bumps on Tomato Stems?

If you are seeing white growths or bumps on the tomato plant stems, all you are probably seeing are roots. Really. Bumps start out as hundreds of tiny hairlets protruding up and down the length of the stalk. These hairlets can turn into roots if they are buried in the soil. Above ground, they become nodules. These nodules are called root initials, adventitious roots, or tomato stem primordial. Basically, they are the earliest developing roots.

What Causes Bumps on Tomato Vines?

Now that we have ascertained what the bumps are, I bet you wonder what causes them. Just as stress can exacerbate or bring on a bout of acne, stress also causes bumps to form on the tomato stalk. Usually, the stress means there’s a blockage in the stem’s vascular system. The plant sends out a hormone called auxin to the tomato’s roots when there is a blockage in a branch. The hormone accumulates in the stem due to the blockage, forming a bump. A number of stressors can engender bumpy tomato stems. Among these are root damage, internal injury, irregular cell growth, high humidity, and probably the most common stress is too much water, either from overwatering or after a deluge, especially if the plant lacks drainage. Sometimes, diseases can result in a tomato stem covered with bumps. These root initials may be white, brown, or the same green as the stem. Bumps may also be caused by exposure to an herbicide. If you see swelling on the stems, check the leaves. If they are curled or stunted, the plant may be affected by an herbicide. Even if you aren’t using one, your neighbor may be. Herbicides can act much like the tomato’s own hormone, auxin, resulting in not only curled leaves but bumpy stems.

What Can Be Done about Bumpy Tomato Stems?

Most of the time there is no need to do anything about bumps on the stems of a tomato. They don’t harm the plant in the slightest. In fact, you can utilize these root initials to help strengthen the plant, simply mound soil around the lower root initials. They will develop into mature roots which, in turn, will strengthen the plant. If you have accompanying wilt, it’s likely that the area is too wet and you have either overwatered or drainage is bad and there has been an abundance of rain. Adjust your watering and be sure to plant your tomatoes in well-draining soil. Wilting can also be an indication of something more sinister such as with fusarium wilt or verticillium wilt. This is accompanied by brown leaves, stunted growth, as well as yellowing and black streaking of stems. Fungicides may help if caught early enough, though pulling up plants and disposing of them may be a better option should this be necessary.

Amy Grant

Amy Grant has been gardening for 30 years and writing for 15. A professional chef and caterer, Amy's area of expertise is culinary gardening.