Tomatoes are the crop most new vegetable gardeners start with, and the one they most often worry about. The plant is forgiving about soil and generous with fruit, but it is fussy about temperature and water. Most of what goes wrong with tomatoes is weather showing up in the fruit, not a missing nutrient.
The short answer
- Plant after your last frost, once the soil has warmed. Minnesota Extension waits for soil at 65°F.
- Plant deep. Bury the stem up to the lowest leaves you keep; it grows roots along the buried part.
- Put in stakes or cages on planting day, and give vining types two to three feet each way.
- Water evenly, about an inch a week, under a layer of mulch. Uneven water causes blossom-end rot and split fruit.
- Feed by a soil test, not by habit. Too much nitrogen early gives big plants and little fruit, and Epsom salts do not help.
- Pick at the first blush of color in hot weather and let the fruit finish indoors.
Determinate or indeterminate?
The plant tag tells you which kind you have, and it decides how you support and prune it.
- Determinate varieties stop growing at a set height and ripen most of their fruit over a few weeks. They suit small spaces, containers, short seasons, and anyone who wants a big batch for canning.
- Indeterminate varieties keep growing and fruiting until frost or disease stops them. They need tall supports and give a long, steady harvest.
When and how deep to plant
Tomatoes are frost-tender, and cold soil stalls them even when the air is mild. Minnesota Extension groups them with peppers, squash, and beans as crops to plant once the danger of frost has passed and the soil has reached 65°F. Plants set out into cold soil sit still for weeks, so an early start gains nothing. The frost date lookup gives your last spring frost, and the seed starting calculator counts back to when to sow indoors.
Plant deep. Tomatoes grow roots along any part of the stem that is buried, which gives a sturdier plant. Minnesota Extension's method for a tall or leggy transplant:
- Dig a trench three to four inches deep instead of a hole.
- Strip the lowest leaves from the transplant.
- Lay the plant on its side in the trench and bury the stem up to just below the lowest leaves you kept. The top will turn upward toward the light within a few days.
Harden transplants off for a week before planting, so they are used to sun and wind. Starting seeds indoors explains how.
Stakes, cages, or a trellis
Put supports in at planting time, before the plant sprawls. Off the ground, fruit rots less, harvesting is easier, and more plants fit in the same space.
The method changes the harvest:
- Stakes give earlier and larger fruit on a narrower plant, but need regular tying and more pruning.
- Cages need little tying and less pruning. The fruit comes a little later and smaller, and the plant is bushier, so the cage must be tall and sturdy enough for the variety.
- A trellis or string supports the plant along a vertical line and goes with the heaviest pruning.
Give vining plants two to three feet in all directions; determinate types can go closer. Crowded plants stay wet longer, which favors leaf spot diseases.
Should you prune the suckers?
Suckers are the shoots that grow in the angle between a leaf and the main stem. Left alone, each becomes another stem that flowers and fruits. Pruning them is optional; it trades the number of fruit for size and earliness.
- Determinate plants need little or no pruning, because most of their fruit forms on those side branches.
- Indeterminate plants can be pruned hard on a trellis, moderately on a stake, and lightly or not at all in a cage. Moderate pruning gives larger, earlier fruit and a more manageable plant.
Pinch suckers off by hand while they are small. Removing the lowest leaves that touch the soil helps keep soil-borne spores off the plant.
Water and feed
Water evenly. About an inch of water a week, from rain or irrigation, is the usual target; the watering guide shows how to check the root zone instead of guessing. What matters most is consistency. A dry spell followed by a soaking causes both blossom-end rot, the dark sunken patch on the bottom of the fruit, and cracks in ripening fruit. Mulch keeps soil moisture steadier and stops rain splashing soil onto the lower leaves.
Feed by a soil test. Too much nitrogen early in the season produces large, leafy plants that set little fruit and can make blossom-end rot worse. If you feed, follow your soil test and hold back nitrogen until the first fruits are developing.
Skip the Epsom salts. Epsom salts are magnesium sulfate. They do not prevent blossom-end rot, which comes from calcium not reaching the fruit, and extra magnesium can make calcium uptake worse. Most soils already have enough magnesium. Clemson and Minnesota Extension both advise adding it only if a soil test shows a shortage.
When to pick
A tomato that has started to blush pink at the blossom end, called the breaker stage, can finish ripening off the vine without losing flavor. Picking then also means fewer cracked fruit.
In hot weather, picking at the first blush is the better choice. Above about 85°F, tomatoes stop making the pigments that turn them red, so fruit can stall green on the vine. Indoors they finish properly: Colorado State Extension gives about two weeks at 70°F and about a month at 55°F.
At the end of the season, pick mature green fruit before frost and ripen it indoors the same way. The frost protection guide covers what to save after a cold night.
Common problems, and what they mean
Most tomato problems are physiological, caused by weather and water rather than disease. Look at where the damage is before treating anything.
| What you see | Usual cause | What to do |
|---|---|---|
| Dark, leathery, sunken patch on the bottom of the fruit | Blossom-end rot: calcium not reaching the fruit, driven by uneven water | Water evenly and mulch; do not add calcium sprays or Epsom salts. See blossom end rot. |
| Rings or lines of cracks around the stem end | Soil moisture swinging between dry and wet, or long rains | Water evenly and mulch; pick at the first blush. |
| Healthy plant, flowers drop without fruit | Hot days and warm nights stop pollination | Wait for cooler weather; do not fertilize. See tomatoes that drop their flowers. |
| Older leaves roll upward but stay green | Physiological leaf roll in hot, dry weather | Nothing; it does not noticeably reduce growth or yield. |
| Spots on the lowest leaves, spreading upward | Septoria leaf spot or early blight | Remove affected lower leaves, mulch, and keep leaves dry. See leaf spots. |
| Large, greasy gray-green blotches; plants collapse fast | Possibly late blight | Act quickly. See blights. |
| Leaves stripped from whole stems, dark droppings below | Tomato hornworms | Handpick, but leave any carrying white cocoons. See caterpillars. |
| New growth twisted, cupped, or strap-like | Often herbicide drift or contaminated compost or manure | See persistent herbicides. |
If the cause still isn't clear, the Plant Doctor walks through the symptoms one question at a time.
Sources and further reading
- University of Minnesota Extension: Growing tomatoes in home gardens — deep planting in a trench, supports at planting, and spacing.
- University of Minnesota Extension: Planting the vegetable garden — planting heat-loving crops after frost, in soil at 65°F or warmer.
- University of Maryland Extension: Growing tomatoes in a home garden — staking, caging, pruning, and picking at first color in hot weather.
- University of Illinois Extension: Do I need to prune my tomatoes? — suckers, and pruning by plant type and support.
- University of Minnesota Extension: Tomato disorders — growth cracks and physiological leaf roll.
- University of Maryland Extension: Cracking of vegetables — soil moisture swings and cracking.
- Clemson Cooperative Extension: Epsom salt in the garden — is it truly needed?
- University of Minnesota Extension: Do common soil health "home remedies" work? — Epsom salts only for a tested magnesium shortage.
- University of Missouri Extension: Growing home garden tomatoes — excess nitrogen and fruit set.
- Penn State Extension: Is this tomato ready to harvest? — the breaker stage.
- University of Illinois Extension: Stalled green tomatoes — why won't they turn red? — heat above 85°F and color.
- Colorado State University Extension: Ripening tomatoes indoors — ripening times at 55°F to 70°F.