How to Care for Tomato Plants: Pruning, Trimming, Bug Control

Tomatoes are often the staple of any home vegetable garden and there are ample reasons why.

The fruit (often mistakenly considered a vegetable) is tasty, relatively easy to grow and is a versatile cooking and salad ingredient.

Once considered poisonous, the tomato has become a popular choice for vegetable gardens across the U.S. with thousands of varieties to choose from.

After planting the seedlings, it's important to give tomato plants proper care and attention, including regular pruning, trimming and bug control.

purple tomatoes
Tomatoes are tasty, relatively easy to grow and provide a versatile cooking and salad ingredient. John Innes Centre UK/Getty Images

Pruning and Trimming Tomato Plants

"Everyone likes to grow tomatoes," Craig LeHoullier, a tomato-growing expert, self-described "tomato nut," author of Epic Tomatoes and co-host of Tomatopalooza, told Newsweek.

"But the areas they grow them in (climatic zones/weather) and methods (garden, raised bed, container, straw bales) vary so widely. There are literally thousands of tomato varieties—and whether they are tall (indeterminate), or short (determinate or dwarf) mean a lot in terms of how they need to be supported."

A good place to start is to remember that tomatoes need plenty of room to spread out and grow, as crowded conditions can inhibit their growth and lead to disease.

Fine Gardening magazine advises that in order to maximize the efficiency of photosynthesis and minimize the risk of disease, each leaf on a tomato plant needs to have plenty of space and should be supported up off the ground.

Space to Grow

If the tomato plant's growth becomes too dense or it is forced to lay on the ground, many of its leaves are diverted into the shade, greatly reducing the amount of sugar it can produce and therefore reducing its capacity to grow.

An overgrown plant also reduces airflow and provides an environment for disease to flourish, Joe Lamp'l, gardening expert and host of the PBS series Growing a Greener World, advises.

"Moving air dries out plant foliage, which is important for disease control," Lamp'l says on his podcast Tomato Growing Advice. "Airborne pathogens may just blow through in dry conditions. However, if plants are wet from morning dew, rain or overhead watering, the fungal spores will cling to the moist foliage. This is how early blight, septoria leaf spot and some other tomato diseases arrive."

Cherry tomato plant
Tomatoes need plenty of room to spread out and grow as crowded conditions can inhibit their growth and lead to disease. myLoupe/Universal Images/Getty Images

Pruning Leaves & Shoots

A good rule of thumb is to watch out for when your tomato plant reaches about 3 feet in height, as the leaves from the bottom foot of the stem should be removed. This is because they are the oldest leaves on the plant and sit at the base of the plant stem, receiving the least amount of sun and airflow. This can lead to potential fungus growth.

Removing and pruning the bottom leaves on a tomato plant helps to prevent fungal diseases from taking hold. When the leaves below the first set of flowers begin to turn yellow, it can be a useful indicator of when to begin pruning.

Clipping off leaves as soon as any spots or deformation become visible is also recommended to stave off the rest of the plant from succumbing to a potential fungal disease.

"Suckers" or "shoots" that grow in the crotch joint of two branches may also be removed from plants so they "do not become top-heavy and topple over," LeHoullier advises.

These growths also won't bear fruit and it is believed they could take energy away from the rest of the plant.

tomato seedlings
A man seen planting tomato seedlings in the greenhouse of a home vegetable garden. Jill Ferry/Getty Images

However, a study from Iowa State University published in 2000 showed that pruning tomato suckers sometimes made a difference and sometimes did not, in terms of the size of the fruit grown.

Thinning out some of the leaves will also allow the sun to better reach the ripening fruit.

Former Cornell Cooperative Extension Horticulture Educator and Master Gardener Marie Iannotti, told The Spruce it is the leaves that give flavor to the tomatoes by photosynthesizing and creating the sugars. Following this logic, fewer leaves could mean fewer sweet tomatoes.

As plants grow, tying the main stems to stakes will give the plants better support.

Most varieties of tomato require some form of support, LeHoullier explains. Indeterminate varieties will continue to grow and put on fruit until they are killed by a heavy frost. Determinate varieties will remain smaller—only about 3 foot tall and 3 inches wide—but they set all their fruit in a short period and the weight can put a lot of stress on the plant's branches.

Supporting tomato plant growth also keeps foliage elevated, at lesser risk of disease and protects tomatoes from pests.

Tomatoes grow on a vine
Tomatoes grow on a vine at a Dutch stand at the Grüne Woche agricultural trade fair on January 17, 2020 in Berlin, Germany. Sean Gallup/Getty Images

Plant Diseases

Tomatoes are susceptible to a range of potentially crop-destroying diseases from airborne pathogens, soil-borne bacterial and fungal pathogens.

One of the most common diseases to affect tomato plants is Alternaria, also known as early blight, and causes dark, half-inch spots on leaves. The spots can spread to a plant's stem which can be fatal. Late blight, a water mold that affects leaves, stems and the fruit, shows up in brown blotches on the leaves and brown rotten fruit.

Inga Meadows, vegetable pathologist at North Carolina State University, believes all tomato disease problems start with the environment.

"On the East Coast [of the U.S.], warm temperatures, high humidity, frequent rainfall and heavy dew all create conditions that are ripe for fungi and bacteria to take hold," she explained on the Lamp'l's Tomato Disease Prevention & Control podcast.

Disease Control

Meadows suggests a helpful way to understand why plant diseases arise is what she terms the "Disease Triangle," where the three points of the triangle are the host, the pathogen and the environmental conditions.

When all three are present, a disease problem is "very likely," she says,

Meadows suggests growing tomatoes in a raised bed and starting out with clean soil or potting mix that is free of soil-borne pathogens.

She also advises to start with healthy transplants from the grower or greenhouse. "If you're at one of your garden centers and you're about to buy a tomato plant that has spots on it, don't do it—resist," she adds.

tomato pest
A farmer shows a tomato damaged by the insect Tuta absoluta. Costas Metaxakis/Getty Images

Meadows also suggests a crop rotation strategy to give the soil a break from a certain crop family every two years or three years so pathogens don't build up in the soil.

Using a drip irrigation system or a soaker hose is helpful in restricting water just to the roots where the plants really need it. Otherwise, apply water at soil level so the foliage itself does not get wet thereby creating an ideal environment for bacteria and fungi.

Simple techniques like removing noticeably affected leaves and disposing of them can slow the spread of disease, or removing an affected plant entirely.

Commonly available fungicide or bactericide sprays must be applied before disease appears to be effective. The sprays coat the leaves, inhibiting a pathogen from infecting the leaf.

Bug & Pest Control

Pests and diseases can infect a tomato crop if proper care and attention are not taken. Pests such as aphids, cutworms, flea beetles and hornworms can wreak havoc on tomato plants, with some worms capable of eating an entire plant in a matter of hours.

Hornworms are the larval stage (caterpillars) of sphinx moths and are called hornworms because of their tell-tale horn or spike on their tail.

These caterpillars have voracious appetites and can consume entire leaves and small stems in a short time, the Missouri Botanical Garden and William T. Kemper Center for Home Gardening warns.

Hornworm
A hornworm caterpillar with wasp eggs on its back is seen atop a leaf. Hornworms can consume entire leaves and small stems in a short space of time. Jim Lane/Getty Images

Aphids are sucking insects that are vectors for plant diseases, gardening expert Lamp'l explains on his website Joe Gardener. However, they can be easily controlled by knocking them off plants with a sharp stream of water or insecticidal soap.

Tomato fruitworm can also leave visible black holes at the base of the fruit stem.

To best manage pests, experts recommend monitoring tomato plants daily, checking under leaves, checking the fruit itself, and checking near the soil.

Small sucking insects such as aphids and mites can be mitigated with a variety of naturally-based insecticides and insecticidal soaps, while larger bugs such as hornworms and stinkbugs can be picked off by hand.

tomato
A ripe tomato hangs from a tomato plant in a front yard. Ben Hasty/Getty Images