Growing tomatoes from seed is one of the most rewarding things a gardener can do. It opens up access to hundreds of varieties that never appear as transplants at garden centers, and it gives you full control over the growing conditions from day one. The process is not difficult, but it does require attention to timing, temperature, and a few key transitions that determine whether your plants produce a modest handful of fruit or an overwhelming abundance.
This guide covers the full arc — from selecting and starting seeds indoors through transplanting, training, feeding, and harvesting. Every stage matters, and the decisions made early (starting date, soil mix, light exposure) ripple through the entire season.
Choosing the Right Seeds
Tomato varieties fall into two broad growth categories that affect every downstream decision. Determinate varieties grow to a fixed height (typically 3 to 5 feet), set fruit over a concentrated 2 to 3 week window, and then decline. They are ideal for canning, sauce-making, and small spaces. Indeterminate varieties keep growing and producing until frost kills them. They need tall supports and more pruning, but they deliver a steady stream of fruit from midsummer through fall.
Beyond growth habit, consider disease resistance. Seed catalogs list resistance codes after variety names — V (Verticillium wilt), F (Fusarium wilt), N (nematodes), T (tobacco mosaic virus), and TSWV (tomato spotted wilt virus). In humid climates or gardens with a history of tomato disease, choosing varieties with multiple resistance codes saves a lot of heartbreak. Popular reliable choices include Celebrity (VFFNT), Mountain Merit (VFF, late blight), and Iron Lady (VFF, early blight, late blight, Septoria).
For flavor, heirlooms remain unmatched. Brandywine, Cherokee Purple, Black Krim, and Mortgage Lifter deliver complex, rich flavor that most hybrids cannot approach. The trade-off is lower disease resistance and sometimes irregular fruit shape — a worthwhile exchange for many home gardeners.
Starting Seeds Indoors
Timing is the single most important factor in seed starting. Tomato seeds should be started indoors 6 to 8 weeks before the last expected frost date in your area. Starting too early produces leggy, root-bound transplants that struggle after planting. Starting too late means the plants will not have time to mature a full crop before fall frost. For detailed guidance on indoor seed starting, the seed starting guide covers timing, soil mixes, and lighting setups in depth.
Soil Mix
Use a sterile seed-starting mix, not garden soil. A good mix contains peat moss or coir, perlite, and vermiculite in roughly equal parts. It should hold moisture without staying soggy. Garden soil introduces disease organisms (particularly damping-off fungi) that kill seedlings before they develop true leaves. Fill cell trays or small pots to within a quarter inch of the rim and moisten the mix thoroughly before planting.
Planting Depth and Germination
Plant seeds a quarter inch deep, two seeds per cell. Cover lightly and press gently. Tomato seeds germinate best at soil temperatures between 75 and 85 degrees Fahrenheit. At 75 degrees, expect germination in 6 to 10 days. At 65 degrees, germination slows to 2 weeks or more and is less reliable. A heat mat under the trays is the simplest way to maintain consistent temperature. Once seedlings emerge, remove the heat mat — the air temperature for growing seedlings should be 65 to 75 degrees during the day and 60 to 65 degrees at night.
Lighting
Seedlings need 14 to 16 hours of strong light per day. A south-facing window rarely provides enough — the plants will stretch toward the light and become leggy within days. LED or fluorescent grow lights positioned 2 to 4 inches above the seedlings are far more reliable. Raise the lights as the plants grow, maintaining that 2 to 4 inch gap. If using a windowsill, rotate trays daily to prevent one-sided leaning.
Thinning and Potting Up
Once seedlings develop their first set of true leaves (the second pair of leaves, which look like actual tomato leaves rather than the smooth seed leaves), thin to one plant per cell by snipping the weaker seedling at soil level. When plants reach 3 to 4 inches tall with 2 to 3 sets of true leaves, pot them up into 3 to 4 inch containers. Bury the stem up to just below the lowest leaves — tomatoes form roots along buried stems, and this deeper planting creates a stronger root system.
Hardening Off
This transition step is critical and often rushed. Seedlings grown indoors under artificial light have thin cell walls and no tolerance for wind, UV radiation, or temperature swings. Moving them directly from indoor conditions to the garden causes transplant shock that can set growth back by weeks.
Begin hardening off 7 to 10 days before your planned transplant date. On day one, place seedlings outdoors in a sheltered, shaded spot for 2 hours, then bring them back inside. Each day, increase the outdoor time by 1 to 2 hours and gradually introduce more direct sunlight. By day 7, plants should be spending the full day outdoors in direct sun and coming in only at night. By day 10, leave them out overnight if temperatures stay above 50 degrees Fahrenheit.
Transplanting
Transplant tomatoes outdoors when nighttime temperatures consistently stay above 50 degrees Fahrenheit and soil temperature is at least 60 degrees at a 4-inch depth. In most zones 5 through 7 gardens, this falls between mid-May and early June. Planting too early into cold soil stalls root growth and makes plants vulnerable to late frost.
Dig a hole deep enough to bury two-thirds of the stem. Remove the lower leaves from the portion of stem that will be underground. This buried stem technique is unique to tomatoes and peppers — it creates an extensive root system that anchors the plant and improves nutrient uptake. Space indeterminate varieties 24 to 36 inches apart. Determinate varieties can go 18 to 24 inches apart. If you are working with raised beds, the living soil raised bed guide covers ideal soil preparation for tomatoes.
Water deeply at planting — at least a half gallon per plant — and add a 2 to 3 inch layer of mulch around (but not touching) the stem. Straw, shredded leaves, or grass clippings all work well. Mulch suppresses weeds, regulates soil moisture, and prevents soil-borne disease spores from splashing onto lower leaves during rain.
Staking and Support Systems
Tomatoes need support. Even determinate varieties benefit from caging. Without support, branches sprawl on the ground, fruit contacts soil and rots, and disease pressure increases dramatically. The three common support methods each have strengths:
- Single stake: A 6 to 8 foot wooden or metal stake driven 12 inches into the soil beside the plant. Tie the main stem to the stake every 12 inches using soft fabric strips or twine. Best for indeterminate varieties grown with aggressive pruning to one or two stems. Low cost, easy to install, but requires consistent tying and pruning.
- Tomato cage: A wire cage surrounding the plant. Commercial cages sold at garden centers are often too short and flimsy. Build your own from concrete reinforcing wire (5-foot tall, 18-inch diameter cylinders) for a cage that actually works. Cages are low-maintenance — no tying needed — and allow the plant to branch naturally. Best for determinate varieties and gardeners who prefer less pruning.
- Florida weave (string trellis): T-posts driven every 4 feet along the row with twine woven between posts on both sides of the plants at 12-inch intervals as the plants grow. Efficient for long rows, used by market gardeners. Requires regular weaving as plants grow but provides excellent support and airflow.
Watering
Consistent, deep watering is the foundation of healthy tomato plants and quality fruit. Tomatoes need 1 to 2 inches of water per week, delivered in 2 to 3 deep soakings rather than daily light sprinkles. Deep watering encourages roots to grow downward, creating drought-tolerant plants. Shallow watering keeps roots near the surface where they are vulnerable to heat and dry spells.
Water at the base of the plant, not overhead. Wet foliage promotes blight, leaf spot, and other fungal diseases. Drip irrigation or soaker hoses are ideal. If hand-watering, use a wand directed at the soil line. Water in the morning when possible — this allows any splash that reaches the leaves to dry before evening, reducing disease risk.
Inconsistent watering — cycles of dry and flood — causes blossom end rot, cracking, and catfacing. A consistent moisture level matters more than the total volume of water.
Feeding Schedule
Tomatoes are heavy feeders that need different nutrients at different growth stages. At transplant, the priority is root establishment — use a balanced fertilizer (10-10-10) or a high-phosphorus starter (like 5-10-5) to encourage root development. Once plants begin flowering, switch to a fertilizer higher in potassium and lower in nitrogen (5-10-10 or similar). Excess nitrogen during fruiting produces lush foliage at the expense of fruit production.
Side-dress with compost or granular organic fertilizer every 3 to 4 weeks during the growing season. If using liquid fertilizer (fish emulsion, kelp extract, or compost tea), apply every 2 weeks. Calcium is critical for preventing blossom end rot — if your soil test shows low calcium, work in gypsum or crusite at planting time.
Pruning Indeterminate Tomatoes
Indeterminate tomatoes produce suckers — new shoots that emerge from the junction between the main stem and each branch. Left unchecked, these suckers grow into full branches that consume energy and reduce airflow. Removing suckers below the first flower cluster directs energy toward fruit production and improves air circulation, which reduces disease.
Pinch suckers when they are small (under 2 inches) to minimize wound size. Above the first flower cluster, you can allow one or two suckers to develop into secondary stems for additional fruit production — this is the two-stem or three-stem training method used by many experienced growers. For more detail on pruning techniques, see the tomato pruning and training guide.
Harvesting at Peak Ripeness
Tomatoes develop their best flavor when allowed to ripen fully on the vine. The fruit should give slightly when gently squeezed and have uniform color with no green shoulders (unless growing a green-when-ripe variety). A ripe tomato releases from the vine with a gentle twist — if you have to tug, it needs more time.
In late season as frost approaches, harvest any fruit that has begun to show color (the "breaker" stage — the first blush of pink or yellow at the blossom end). These will ripen indoors on a countertop at room temperature within a week. Fully green tomatoes can be ripened in a paper bag with a banana (the ethylene gas from the banana accelerates ripening), but their flavor will be inferior to vine-ripened fruit.
Pick regularly — every 2 to 3 days during peak season. Leaving ripe fruit on the vine signals the plant to slow down production. Consistent harvesting keeps the plant producing at full capacity.
Common Problems and Solutions
| Problem | Cause | Solution |
|---|---|---|
| Blossom end rot | Calcium deficiency, inconsistent watering | Mulch, even watering, add gypsum |
| Cracking | Heavy rain after dry spell | Consistent watering, mulch heavily |
| Blossom drop | Night temps below 55°F or above 75°F | Wait for moderate temps, shade cloth in heat |
| Early blight | Fungal (Alternaria), soil splash | Mulch, prune lower leaves, fungicide |
| Hornworms | Manduca caterpillars | Hand-pick, Bt spray, encourage parasitic wasps |
| Leaf curl | Environmental stress, virus | See leaf curl causes and fixes |
Frequently Asked Questions
How many tomato plants does a family of four need?
For fresh eating, 4 to 6 indeterminate plants provide a steady supply through the season. For canning and sauce-making, add 6 to 10 determinate plants that produce a concentrated harvest. A total of 10 to 16 plants covers most families comfortably, assuming good growing conditions and variety selection matched to your climate.
Why are my tomato plants tall but not producing fruit?
Excessive nitrogen fertilizer is the most common cause. High nitrogen drives vegetative growth (leaves and stems) at the expense of flowering and fruit set. Switch to a low-nitrogen, high-potassium fertilizer. Other causes include insufficient sunlight (tomatoes need at least 6 to 8 hours of direct sun) and nighttime temperatures outside the 55 to 75 degree range for pollination.
Can tomato seeds be saved for next year?
Yes, but only from open-pollinated and heirloom varieties. Seeds saved from hybrid varieties (F1) will not grow true to type — the offspring will vary unpredictably. To save seed, scoop the seeds and gel from a fully ripe tomato into a jar, add an inch of water, and let it ferment for 2 to 3 days until a mold layer forms. Rinse the seeds clean, dry them on a paper plate for a week, and store in a labeled envelope in a cool, dry place. Properly stored tomato seeds remain viable for 4 to 6 years.
What is the best mulch for tomatoes?
Straw is the classic choice — it suppresses weeds, holds moisture, and does not compact. Shredded leaves work well and break down into soil amendments over the season. Grass clippings are effective but should be applied in thin layers (1 inch at a time) to prevent matting and odor. Avoid fresh wood chips directly against the stem, as they can harbor fungi. Black plastic mulch warms the soil early in the season, which is helpful in cold climates, but it does not add organic matter and must be removed at season end.
How late in the season can tomatoes be planted?
Count backward from your first expected fall frost date. Indeterminate varieties need at least 80 to 100 days from transplant to first ripe fruit. Determinate varieties need 60 to 80 days. Add 2 weeks as a buffer. In zone 7 with a mid-October frost date, the latest practical transplant date for determinate varieties is around July 15, and for indeterminate varieties around July 1. Using larger transplants (gallon-size rather than cell packs) shaves 1 to 2 weeks off the timeline.