Growing Tomatoes: Common Mistakes and Como to Avoid Them

Tomatoes are the most popular home garden crop in North America and also the one that generates the most frustrated questions. Most problems trace back to a handful of common mistakes that are easy to fix once you know what to look for. If your tomatoes have been underperforming, chances are good that one of these issues is the culprit.

Planting Too Early

Tomatoes are warm-season plants that stop growing when soil temperatures drop below 55 degrees Fahrenheit.

Planting transplants outside before the soil has warmed up does not give you a head start. It gives you stunted plants that sit in cold dirt and sulk. In most of the northern US, that means waiting until late May or early June, even though garden centers start selling tomato transplants in April. Use a soil thermometer pushed 4 inches into the ground. When it reads 60 degrees consistently for a week, you are safe to plant.

Black plastic mulch laid over the bed two weeks before planting raises soil temperature by 5 to 8 degrees and can buy you an earlier planting window.

Watering Inconsistently

Tomatoes need about 1 to 1.5 inches of water per week, delivered consistently. The keyword is consistently. Letting the soil dry out and then flooding it causes blossom end rot, a calcium deficiency triggered not by lack of calcium in the soil but by irregular water uptake that prevents calcium from reaching the fruit.

It also causes fruit cracking, where the skin splits as the fruit expands too quickly after a heavy watering following a dry spell. A drip irrigation system on a timer eliminates this problem entirely. If you water by hand, water deeply at the base of the plant every 2 to 3 days rather than lightly every day. Shallow watering encourages shallow roots that dry out faster.

Not Pruning Indeterminate Varieties

Indeterminate tomatoes, the ones that keep growing all season, produce suckers at every leaf node.

A sucker is a new stem that grows in the V between the main stem and a branch. Left alone, each sucker becomes a full branch that produces its own suckers. By midsummer, an unpruned indeterminate tomato is a dense jungle where air cannot circulate and sunlight cannot reach the interior fruit. Pinch suckers when they are small, 2 to 3 inches long, by snapping them off at the base. Keep the main stem and the first two or three strong suckers that develop low on the plant.

This gives you a manageable structure with good airflow. Determinate varieties (the ones labeled "bush type") should not be pruned since they set all their fruit at once on a fixed number of branches.

Ignoring Soil Preparation

Tomatoes are heavy feeders that need rich, well-draining soil with a pH between 6.2 and 6.8. Planting them in unimproved clay or sandy soil without amendments leads to poor growth and low yields. Before planting, work 2 to 3 inches of finished compost into the top 8 inches of soil. Add a balanced granular fertilizer like 10-10-10 at the rate recommended on the package, typically 2 tablespoons per plant mixed into the planting hole.

For raised beds, a mix of 60 percent topsoil, 30 percent compost, and 10 percent perlite provides good drainage and fertility. Test your soil pH with a $15 kit from any garden center. If pH is below 6.0, add lime at the rate indicated by your test results.

Planting Too Shallow

Tomatoes are one of the few vegetables that benefit from deep planting. Every bit of buried stem develops new roots, creating a stronger, more drought-resistant plant.

Strip the leaves from the bottom two-thirds of the transplant and bury the stem up to the remaining top leaves. A 12-inch transplant should go into a hole 8 inches deep. If your soil is heavy clay and you cannot dig that deep, lay the stem sideways in a 4-inch trench with the top leaves sticking up. The buried stem will develop roots along its entire length and the top will bend upward toward the sun within a few days.

Crowding Plants Together

Spacing matters more than most gardeners realize.

Indeterminate tomatoes need 24 to 36 inches between plants. Determinates need 18 to 24 inches. Crowded plants compete for water, nutrients, and light. Worse, the reduced air circulation creates a humid microclimate that invites fungal diseases like early blight and septoria leaf spot. These diseases overwinter in soil and splash onto lower leaves during rain. Good spacing combined with mulch that covers the soil surface reduces disease pressure significantly.

If you have limited space, grow fewer plants with proper spacing rather than cramming in extras.

Skipping Support Structures

Every tomato plant needs support. Even compact determinate varieties flop over when heavy with fruit. For indeterminate varieties, a 6-foot steel cage or a sturdy stake with ties is the minimum. The flimsy cone-shaped cages sold at most garden centers are too short and too narrow for anything except cherry tomatoes.

The best support system is the Florida weave, which uses stakes every 2 plants with twine woven between them, creating a wall that supports the plants from both sides. It costs about $0.50 per plant in materials and lasts the entire season. Set up your support system at planting time. Trying to cage or stake a 4-foot plant in July damages roots and breaks branches.

Overfertilizing with Nitrogen

Too much nitrogen produces gorgeous, dark green foliage and almost no fruit. Tomatoes need balanced nutrition with an emphasis on phosphorus (the middle number in fertilizer ratios) for flower and fruit development. A fertilizer like 5-10-10 or 4-8-4 applied when the first fruits begin to set gives the plant what it needs without pushing excessive leaf growth. Side-dress with a tablespoon of granular fertilizer per plant every 3 to 4 weeks, working it into the top inch of soil 6 inches from the stem. Organic options like fish meal, bone meal, and kelp meal release nutrients slowly and are harder to over-apply. Stop fertilizing once plants have set their main crop of fruit, usually about 6 weeks before your expected first frost date.