Planting Tomatoes

Planting tomatoes goes well when three things line up: warm soil, a hardened-off seedling, and a deep hole. Miss one and the plant stalls.

Getting tomato seedlings in the ground at the right time is the difference between a plant that takes off and one that stalls for weeks. The key signal is soil temperature, not the calendar date - tomatoes need soil at least 60°F at the root zone before they will actively grow, and most planting failures come from rushing that window. This guide covers how to choose healthy seedlings, harden them off properly, amend the soil, and transplant them deep enough to build a strong root system.

In short:
• Plant when soil temperature hits 60°F minimum at 4 inches deep - not just when air temperatures feel warm
• Harden off all seedlings for 7–10 days before planting, even store-bought ones
• Bury the stem deep, up to the lowest leaves - to build a wider, more drought-resistant root system
• Add compost and slow-release fertilizer before planting; bone meal at the hole bottom gives roots an early phosphorus boost

How to Plant Tomatoes in the Ground: 7 Steps

How do you plant a tomato? Wait for warm soil, toughen up the seedling, then bury it deep. Here is the order to do it in.

1. Wait for warm soil. Plant after your last spring frost, once the soil reads at least 60°F at 4 inches deep.
2. Harden off the seedlings for 7 to 10 days. Give them a little more outdoor time each day.
3. Pick a spot in full sun with soil that drains well.
4. Water the seedlings 1 to 2 hours before planting. Plant on a cloudy day or in the late afternoon.
5. Dig a deep hole and mix in compost. Pinch off the lowest leaves and bury the stem up to the next set.
6. Firm the soil around the stem and water generously.
7. Set a stake or cage right away, then spread an inch of mulch.

Each step is covered in detail below.

When to Plant Tomatoes Outdoors

When to plant tomatoes depends on the soil, not the date. Wait until your last spring frost has passed, the soil reads at least 60°F at 4 inches deep, and nights stay above 50°F.

Tomato plants are essentially tropical plants, needing warm days and cool nights. They prefer soil temperatures between 70°F and 75°F. They (drop)blossoms if air temperature is cooler than 55°F or hotter than 90°F and are very sensitive to frost, which blackens and kills them.

Tomatoes need at least 6 to 10 hours of sun daily plus some afternoon shade in really hot climates.

They accept almost any kind of soil, as long as it has lots of organic matter in it to help it hold moisture and drain well and is on the acid side (pH 6.0 to 7.0).

Add organic matter such as peat moss, chopped leaves or compost to lighten and loosen clay soil or plant tomatoes in raised beds to improve soil drainage.

Mix in some all-purpose slow-acting organic granular fertilizer or a fertilizer product for acid-loving plants when preparing the soil. Follow directions on the package label.

Where to Plant Tomatoes: Full Sun, Good Drainage and a Fresh Bed

Plant tomatoes in the sunniest spot you have, in soil that drains well. Skip any bed that grew tomatoes, peppers, potatoes, or eggplant in the last two years. Those crops share diseases that stay in the soil, and Cornell’s tomato growing guide recommends that two-year gap. Low spots where water sits after rain are a poor choice too.

No good ground? Tomatoes in containers covers pot size, potting mix, and which plant types suit a patio.

What to Check on a Tomato Seedling Before You Plant It

When buying tomato plants at the garden center or farmer’s market, look for deep green leaves and for stocky, short plants that look healthy. Check the pot to see if the soil is moist and rich-looking. Pull one or two out of their container and see if the plant is root bound.  Do not buy wilted plants or plants with yellow leaves. Especially be sure you know which of your tomato plants are determinate (grow 4 or 5 feet) or indeterminate (grow over 7 feet).  And, don’t forget to protect your plants from the elements on the drive home. Translation: Don’t put them in the back of an open pickup and then fly home on I-5.

Grew your own instead of buying? The same checks apply. Start tomatoes from seed covers sowing indoors and raising sturdy transplants.

Still deciding what to grow? Varieties of tomato sorts the choices by plant size, ripening time, and use.

How to Harden Off Tomato Seedlings Before Planting

To harden off tomato seedlings, set them outside a little longer each day for 7 to 10 days before planting. You should not even think of planting tomato seedlings until the soil temperature is at least 65 degrees; 70 degrees is better.  When the soil temp is okay then you need to bring your seedlings outside during the day and then bring then back inside at night for at least two days.  This helps the seedlings get used to real sun and the breezes. 

Two days is the bare minimum. A week to 10 days works better, and that goes for store-bought plants too, since most come straight from a greenhouse. Start with an hour in a shaded, sheltered spot. Add an hour or so each day, and move the plants into more sun as you go. Bring them in on any night forecast below 50°F.

On soil temperature, 60°F is the floor. At 65°F to 70°F, roots settle in faster, so waiting a few extra days costs you nothing.

How to Transplant Tomato Seedlings Step by Step

To transplant tomato seedlings, water them first, plant late in the day, and set them deeper than they grew in the pot.

1. Water seedlings well 1 to 2 hours prior to planting, to keep their rootballs intact during the transplanting process.
2. Plant on a cloudy day or in late afternoon or evening to protect seedlings from the hot sun while they cope with transplant shock. The soil is cooler and the relative humidity higher then, reducing moisture stress on the new plants.
3. Space transplants 1½ to 2½ feet apart. With a trowel dig individual holes a bit deeper than the seedling’s rootball or container. Deep planting encourages roots to form along the buried stem, increasing the plant’s capacity to take up water and nutrients, resulting in stronger plants.
4. Gently coax each seedling from its container, set it in its hole and fill in with loose dirt. Press the soil gently around the main stem. Water transplants generously and then do not allow them to dry out.
5. Drench the soil around each seedling with Actinovate and with Thrive. 
6. Apply an inch of organic mulch around the seedlings.  After they get large enough add mulch until the depth is 3 to 4 inches. 

Planting tomato seedlings deep is worth the extra digging. Pinch off the lowest leaves and bury the stem up to the next set. Is the seedling tall and leggy? Dig a trench 3 to 4 inches deep instead, lay the stem on its side, and bend the top gently upward before you cover it. Roots form along the buried stem either way.

Put your stake or cage in on planting day. Driving one in later can damage roots that have already spread. Support for tomatoes covers stakes, cages, and how to tie the stems.

How Far Apart to Plant Tomatoes

Plant tomatoes 2 to 3 feet apart in most home gardens. That is the spacing The Old Farmer’s Almanac gives.

You can go closer if you stake and prune. Cornell’s tomato growing guide lists 12 to 24 inches for determinate plants, 14 to 20 inches for staked indeterminate plants, and 24 to 36 inches for indeterminate plants left to sprawl. Treat those as minimums. Crowded plants get less sun and less air.

Not sure which type you have? Check the plant tag. Planning a full bed? How many tomato plants helps you set the count before you dig.

Best Soil Amendments for Planting Tomatoes

The best soil amendments for planting tomatoes are compost, mycorrhizal fungi, and beneficial soil microbes, added at each planting hole.

Critical New Products To Make Planting Tomatoes A Huge Success

There are three new garden products and one old one that have become essential at planting time to our success in growing wonderful tomatoes.

Compost – Available forever, compost is incredibly valuable when included in the soil where you are planting tomato seedlings – we use a half a cup per plant. 

Myke – Myke contains mycorrhizae which are beneficial fungi that attach themselves to the roots of a plant and literally double the size of the plant’s root system in a few weeks.  This significantly increases a plant’s access to water and nutrients.  It’s crazy not to use this product – a tablespoon per plant on the root ball and in the planting hole. 

Actinovate – Actinovate is a biological organic fungicide that has the very powerful ability to prevent virtually every fungal disease that affects tomatoes including early blight, fusarium, verticillium, and late blight. You spray it on the root ball and on the plant at planting time and then spray the plant every two weeks throughout the season.  Available on Amazon.com. 

For a full list of tomato diseases and pests Actinovate protects against, see Problems of Tomatoes.

Vegetable Thrive – Thrive contains Microbial Soil Bacteria and Mycorrhizal Fungi; two groups of beneficial microbes found only in very healthy soil with an organic content of at least 5%.  Most of us do not have soil with 5% organic matter or higher so Thrive provides the services of critical beneficial soil microbes as we work to get our soil up to organic snuff.  Available on Amazon.com.  Spray on plants at planting and then spray plants every three or four weeks throughout the season.

That is what goes in the hole on planting day. Soil care for tomatoes explains what compost, mycorrhizae, and soil microbes each do, and how to prep the whole bed in spring.

Common Questions About Planting Tomatoes

What soil temperature do tomatoes need before planting?

Tomatoes need a soil temperature of at least 60°F at a 4-inch depth before planting - 65°F is better for faster establishment. Soil temperature lags behind air temperature by two to three weeks in spring, so a warm afternoon does not mean the ground is ready. Use an inexpensive soil thermometer, push it 4 inches deep in the morning for the most accurate reading.

How deep should you plant tomato seedlings?

Plant tomatoes deep - bury the stem up to the lowest set of leaves, pinching off any leaves that would be underground. Tomatoes are one of the few vegetables that grow roots directly from buried stem tissue, so a deeper hole means more root surface, better water uptake, and a plant that holds through dry spells. A planting hole 6 to 8 inches deep handles most transplants.

Do tomatoes need to be hardened off before planting?

Yes, hardening off is essential for any tomato seedling grown indoors or bought from a greenhouse. Without it, plants go into shock from direct sun, wind, and temperature swings they have never experienced. The process takes 7 to 10 days: start with one hour outdoors in a shaded spot, add an hour each day, and work up to full sun and longer exposure before planting in the ground.

When is the best time to plant tomatoes outside?

Plant tomatoes outdoors when two conditions are both true: nighttime air temperatures stay reliably above 50°F, and soil temperature is at least 60°F at 4 inches deep. For most US gardeners this window falls two to three weeks after the last frost date for their zone - which ranges from early March in zone 9 to late May in zone 5. Soil temperature is the more reliable signal; the calendar date is only a rough guide.

What should you add to the soil before planting tomatoes?

Work compost and a balanced slow-release fertilizer into the bed before planting. If the soil is heavy clay or sandy, the compost matters more than any specific amendment. Drop a tablespoon of bone meal at the bottom of each planting hole for an early phosphorus boost. Skip the crushed eggshells. They do not prevent blossom end rot, which usually comes from uneven watering, not a lack of calcium in the soil.

Warm Soil and a Deep Hole Do Most of the Work When Planting Tomatoes

Planting tomatoes successfully takes soil at 60°F or warmer, a seedling hardened off for 7 to 10 days, and a hole deep enough to bury the stem up to its lowest leaves.

Once the seedlings are in the ground - planted deep, amended well, and given a week to adjust, the foundation is set. Watch the first two weeks after transplanting: afternoon wilting is normal while roots establish, but if plants are still drooping in the evening, they need water. After that, move on to watering schedules, fertilizing through the season, and what to watch for as the plants grow - all covered in Caring For Tomatoes.