8 Problem Causing Mistakes Tomato Plant Growers Make!

Most tomato trouble starts before the first fruit ever forms. Seedlings shocked by the move outdoors, plants crammed too close together, a spot with too little sun: each one is easy to avoid once you know it’s a problem. Here are ten common mistakes, with the fix for each, based on university extension advice. New to growing tomatoes? Start with our guide to basic tomato plant care.

Mistake #1 – Skipping the Hardening-Off Step

Tomato seedlings raised indoors or in a greenhouse have never dealt with wind, cold, or full sun. According to Nebraska Extension, once outside they lose water faster from heat, sunlight, and wind, and strong outdoor sun can easily sunburn the leaves of plants that were not hardened off. Hardening off gives them time to toughen up before they go in the ground.

Here’s how to do it:

• Start 7 to 10 days before you plan to transplant. Harden plants off gradually over that period. Clemson Extension says to start a week before transplanting, and UNH Extension says about ten days.
• On day one, set the seedlings in a shaded spot for 2 to 3 hours, sheltered from strong wind, then bring them back inside.
• Each day, add a few more hours outside and a little more sun.
• Watch the soil moisture. Guides differ: some say to cut back on watering gradually without letting the seedlings wilt, while others note seedlings dry out faster outdoors and need more frequent watering. Check them every day and don’t let them wilt.
• Skip the cold nights. Bring plants indoors at night and on days when temperatures fall below 60°F, because tomatoes can suffer chilling injury below that.

Count back from your planting date so the seedlings finish hardening off right when the weather is ready for them.

Mistake #2 – Not Doing Anything About the Soil

Tomatoes do best in soil that has been prepared before planting. Choose a well-drained site. Have your soil tested through your local Extension office and work in organic materials such as composted manure before planting, or add compost in spring or fall.

A soil test also tells you your pH. Extension guides give slightly different targets: 6.2 to 6.5, 6.0 to 6.5, or 6.2 to 6.8. The goal is soil that is well amended with organic compost.

Related: Epsom Salt For Tomatoes: What It Actually Does (and When to Use It)

Mistake #3 – Planting Tomatoes Too Close

It’s tempting to squeeze in extra plants, but crowding works against you. Dense foliage holds humid air around the plants. Higher humidity from heavy foliage may let leaf diseases and fruit rots spread more easily, and spacing plants adequately apart is one way to increase airflow against early blight.

How far apart is far enough depends on how you support the plants. Iowa State Extension gives these spacings:

• Determinate tomatoes: 2 to 2½ feet apart.
• Indeterminate tomatoes on stakes: 1½ to 2 feet apart in the row.
• Indeterminate tomatoes in wire cages: 2½ to 3 feet apart. Our guide to building the ultimate tomato cage shows one way to support them.
• Indeterminate tomatoes left to sprawl: 3 to 4 feet apart.

Other guides run tighter for supported plants: 18 to 24 inches for staked or caged plants, or 24 inches, and the Florida vegetable planting guide lists 18 to 32 inches for supported tomatoes. For more detail, see how much space a tomato plant needs.

Whichever spacing you choose, support the plants. Stake your plants to keep the fruit off the ground and help conserve space, and you can use tomato cages to trellis them, too.

Mistake #4 – Planting the Wrong Tomato Varieties

Pick a variety that fits your space and your season. Tomatoes come in two growth habits.

Determinate Tomatoes

Determinate, or bush-type, plants stay compact. They stop growing and produce a set number of fruits that all ripen within a four- to six-week period, and they do not need pruning, staking, or trellising. Still, most tomatoes can benefit from staking or trellising to help keep fruit off the ground, and a determinate variety gives just a single crop. If your garden plot is small or you plan to grow tomatoes in containers, bush-type plants may be the only option.

Indeterminate Tomatoes

Indeterminate, or vining, plants keep growing. They need support such as cages, stakes, or trellises and keep flowering and ripening fruit until the weather turns too cold. They also have a large, sprawling growth habit, will require pruning and support, and produce fruit over a period of several months.

Two more things to match to your garden. First, disease resistance. Choose varieties resistant to known tomato diseases, including Verticillium wilt and Fusarium wilt; these qualities are usually noted on the label by short letter codes. Fusarium wilt can destroy an entire tomato crop, and the letters F, FF, or FFF after a cultivar name indicate resistance to races 1, 2, and 3. Utah State University Extension says Fusarium and Verticillium wilt are both soilborne fungal diseases that can survive in the soil for many years, and that once a plant is infected there is no treatment or cure, so management should focus on prevention.

Second, heat. Once average nighttime temperatures climb above about 80 degrees, large-fruited tomatoes keep flowering but stop setting fruit, while cherry and grape tomatoes typically perform well through Florida summers.

Mistake #5 – Planting Tomatoes in Shade

So, how much sun do tomatoes need? UF/IFAS says at least four to six hours a day, and its Florida vegetable gardening guide says to choose a garden site with at least six hours of direct sunlight daily. Maryland Extension says full sun means direct light at least 6 hours a day, and that tomatoes prefer 8 to 10 hours. Tomatoes need full sun for good fruit production.

Trees, roofed decks, and nearby houses can all cast shade, so watch the spot through the day before you plant. If you’re growing in lightweight containers, you can move them around the yard to follow the sun.

Mistake #6 – Never Pruning Indeterminate Tomatoes

Indeterminate tomatoes need some pruning to stay manageable. The shoots to look for are called suckers, which grow in the angle where a leaf branch meets the main stem. Moderate pruning will increase fruit size, hasten ripening, and keep your plants more manageable. Pruning can also improve harvestable yields, prolong the harvest season, and help reduce some disease problems. Bush-type determinate plants do not need pruning.

How many stems to keep depends on who you ask: two to three main stems, one or two, or one to three for staked plants. Shoots are easy to pinch off by hand. There’s also a trade-off: caged tomatoes pruned only once develop heavier foliage, and humidity may be higher, which may allow foliar diseases and fruit rots to spread more easily. When you prune tomato plants, keep leaves and airflow in mind.

We like these hand pruners.

Why Felco #2 Pruners Are The Best Hand Pruners On The Market

Clean your tools, too. Wash and sanitize pruning tools after touching infected plants, so make sure you sterilize your pruning shears after cutting a plant that shows disease symptoms.

Mistake #7 – Not Ready for Early Blight

Early blight is one of the most common tomato diseases. Minnesota Extension says severe defoliation can occur, and the fungus overwinters in infected plant debris and soil. Lower leaves get infected when they touch contaminated soil, including when raindrops splash soil onto them.

Here’s how to spot it. Small dark spots form first on older leaves near the ground. Larger spots have target-like concentric rings, and the tissue around the spots often turns yellow. Severely infected leaves turn brown and fall off.

What helps:

• Rotate. Let two years pass before you plant tomatoes or peppers in the same location. For a longer rotation, choose a site where tomatoes, peppers, eggplant, or potatoes have not been grown for at least three years, which helps avoid soil-borne diseases and nematodes.
• Cover the soil under the plants with mulch, water at the base of each plant, and stake or trellis for airflow.
• Prune the bottom leaves. That can prevent spores from splashing up from the soil onto leaves.
• Remove spotted leaves. It is okay to remove up to one-third of the plant’s leaves if you catch the disease early, but not more than that.
• Look for resistant varieties. Resistance does not mean you will never see early blight, but the damage will be less severe.

As for spraying, most home gardeners don’t need to treat tomatoes with a fungicide, because tomato plants can tolerate a lot of early blight without producing fewer tomatoes.

Related: What Causes Blossom Drop in Tomato Plants?

Mistake #8 – Overfertilizing Your Tomato Plants

Tomatoes do need nutrients, but more isn’t better. Too much nitrogen fertilization leads to plants that are bushy, leafy, and slow to bear fruit, with lush, vigorous foliage but little fruit production. Excess nitrogen can also contribute to blossom end rot, because the extra leaf growth redirects water and calcium from the developing fruit to the leaves.

Let a soil test guide you. A soil test is the best method of determining what the crop needs, and you may not need additional fertilizer, depending on how much organic matter you apply. When you do feed, compare the best fertilizer for tomatoes and follow the label.

Mistake #9 – Watering Unevenly

Erratic watering causes trouble, and blossom end rot is the classic result. Calcium travels up the plant in water, so if watering is erratic, the supply of calcium to the developing fruit is erratic too and may be missing when needed. Blossom end rot is caused by a shortage of calcium in enlarging fruits, and inconsistent watering is among the factors that encourage it. Once a fruit has it, that fruit can’t be fixed, so prevention is the plan.

Here are the tips that matter most:

• Aim for steady moisture. Give about one to two inches of water per week, with a heavy soaking once a week preferred to several light sprinklings, and water deeply and regularly during dry periods. Try a consistent watering schedule with soaker hoses and learn about deep watering tomatoes.
• Mulch. Mulch helps the soil retain moisture; keep plants well mulched and watered throughout the growing season.
• Water the soil, not the leaves. Water at the base of each plant with drip irrigation, a soaker hose, or careful hand watering; wet leaves, especially in the evening, can cause leaf diseases.
• Don’t overdo it. Plants may decline and die when their roots are too wet, and too much water at any one time may cause ripening fruit to split. Here’s why tomatoes crack.

Mistake #10 – Hanging Tomatoes Upside Down Without a Plan

Upside-down planters look simple, but Colorado State University Extension points out several catches. A planter filled with damp soil and a large tomato plant can weigh 50 pounds, so all of the hardware has to be strong enough to hold it. Trees, roofed decks, and nearby houses cast shade, and the planter itself can shade a young plant.

Choose the variety and container with care. Cherry and other small-fruited tomatoes are better suited to upside-down growing, and a small rooting volume (one brand’s planter called for two pounds of soil) would not support a large tomato plant in Colorado’s hot, windy climate. Buckets are preferred over thin, breathable plastic planters, which dried out so quickly that watering even once a day was not enough. In Colorado’s windy weather, the weight of the stems can pull or break off the stem.

The bottom line: upside-down planters are an option if you can’t grow tomatoes right side up for reasons of space or sunlight. Otherwise, it is easier to grow them right side up.

Get these ten right and you’ll sidestep most of the planting-stage trouble that holds tomatoes back. For more on a bigger harvest, see our guide to high-yield tomatoes. Which mistake has tripped you up the most?