Growing tomatoes

When to plant

Tomatoes have no frost tolerance, so they go into the garden after your typical last spring frost, not before. Extension services advise waiting until the danger of frost has passed and the soil has warmed ^[1]. A soil temperature of about 60°F is a common target ^[3][4]. Cornell suggests waiting one to two weeks past the last frost, until nights stay above about 45°F ^[2]. Your typical frost date is an average, not a promise, so a few extra days of patience rarely hurts.

Most gardeners set out transplants rather than sowing seed in the garden. Plants started indoors need about five to eight weeks before they’re ready to go out ^[1][3]. If a cold night follows planting, be ready to cover young plants. Tomatoes chilled by cold nights can take up to two weeks to start growing again ^[13].

Varieties range from about 55 days to three months from transplant to the first ripe fruit ^[3]. Check the “days to maturity” on the label against the length of your warm season.

Through the season

Young plants. After transplanting, keep the soil evenly moist while roots settle. Tomatoes need about 1 inch of water a week from rain or watering ^[1][2], and Utah State suggests 1–2 inches ^[4]. Rather than watering on a fixed schedule, check first. UC Master Gardeners suggest watering established plants when the soil is dry about 2–3 inches down ^[19]. Give plants room: vining (indeterminate) types need about 2–3 feet in each direction ^[1].

Flowering. Small yellow flowers appear along the stems. Plants need at least 6 hours of direct sun to flower and set fruit well ^[17][8]. Too much nitrogen fertilizer pushes leaves at the expense of flowers ^[17]. Flowers are also sensitive to temperature, and very hot days or cool nights can make them fall off (see Weather that matters).

Fruit forming. Green fruit swells over several weeks, and it takes about six to eight weeks for fruit to ripen and color ^[5]. Keep soil moisture even through this stage. Swings between dry and wet soil are linked to blossom-end rot and cracked fruit, and a layer of mulch helps ^[17][6].

Ripening. Fruit shifts from dark green to a lighter green, then shows a blush of color ^[12]. From there it can finish on the vine or indoors (see Harvest). In western Washington, WSU suggests removing new blossoms and small fruit on large-fruited varieties from mid-August, so the plant puts its effort into fruit that can still ripen before the season ends ^[20].

Finished. Frost ends the season for tomatoes. Clear out old plants afterward, since the fungi behind common leaf spots survive on plant debris ^[17].

Weather that matters

Frost. Tomatoes are damaged or killed by frost ^[18]. The National Weather Service explains that frost can form when the official low is only about 36–37°F. On clear, calm nights, air near the ground can be 5°F or more colder than at thermometer height ^[14]. When frost is possible, pick fruit that shows color and cover the plant with sheets, blankets, or frost cloth held off the leaves. Remove the cover once temperatures climb above freezing ^[15]. Covers work by holding in heat from the soil. Fabric row covers give up to about 10°F of protection, depending on the fabric ^[16], but covering usually stops helping below about 28°F ^[15].

Cool nights in late season. Well before frost, nights at or below about 50°F slow ripening ^[12]. UConn Extension suggests starting to pick green fruit once temperatures dip below 50°F for a day or two ^[9]. Commercial handling guides put the chilling point at 55°F, because damage builds up over days in storage ^[10]. Sources range from about 50°F to 55°F.

Heat. Hot weather is a common reason tomato flowers drop. Extension sources put the trouble range at days above about 85–95°F and nights above about 70–75°F ^[5][6][7][2], and the effect grows the longer the heat lasts ^[7]. Plants usually set fruit again once temperatures ease ^[7][19]. There’s little to fix, but check soil moisture during the heat, since dry soil adds to flower loss ^[7]. For hot summers, heat-set varieties hold their flowers better ^[7]. Heat also affects color: above about 85°F, red pigment forms poorly, and fruit left on the vine can ripen yellow-orange ^[5][6].

Cool nights while flowering. Nights below about 55°F can also keep fruit from setting ^[2][7]. Utah State gives 50°F ^[4]. Cold during fruit set can leave fruit scarred and misshapen ^[17].

Dry spells and heavy rain. Uneven moisture is behind several fruit problems. A dry stretch followed by heavy rain or a big watering can make ripening fruit crack ^[17]. In Hawaii, UH suggests picking more often when heavy rain is causing splits ^[21]. During dry spells, check before you water: push a finger into the soil near the plant, and if it’s dry at the first knuckle, water deeply at the base.

Harvest

For the best flavor, many gardeners wait until fruit reaches full color for the variety ^[19]. You can also pick earlier. Fruit picked once the blossom end shows pink ripens about as well off the vine ^[6], and fruit at the “breaker” stage, with first color on up to a tenth of the skin, ripens normally indoors ^[10]. Picking early can cut losses to cracking and pests ^[6][21]. Sources differ on flavor: UH notes that fruit picked three-quarters to fully ripe tastes better than fruit picked earlier ^[21].

In very hot weather (above about 85°F), Texas A&M suggests picking at the pink stage and letting fruit color indoors ^[6]. The best range for ripening is about 68–77°F ^[12][5].

Before the first fall frost. Pick fruit that shows any color, plus full-size green fruit that has turned pale, whitish green ^[11][4]. Ripen it indoors, not in the fridge. Mature green fruit takes about 2 weeks at 65–70°F and 3–4 weeks at 55°F ^[9]. Wrapping fruit one by one in paper and storing it at about 60–65°F spreads ripening over several weeks ^[11][13]. Check it weekly and use fruit as it colors ^[9]. You can also pull a whole plant and hang it in a sheltered spot so its fruit keeps ripening ^[11]. Keep unripe fruit out of the refrigerator, where it can be chilled and ripen poorly ^[6][10].

Common problems

Flowers drop without making fruit

What it looks like: Flowers open, then yellow at the stem and fall off. Few new fruit form.

Likely causes: Days above about 90°F or nights above about 75°F, cool nights below about 55°F, dry soil, less than 6 hours of sun, or too much nitrogen ^[17][6].

What to do: Wait out the weather, since plants usually set fruit again when temperatures ease ^[7]. Check soil moisture, keep mulch in place, and hold off on high-nitrogen fertilizer ^[17]. If your summers run hot, try heat-set varieties next season ^[7].

When to ask an expert: If flowers keep dropping for weeks in mild weather, with good sun and steady moisture.

Blossom-end rot

What it looks like: A water-soaked spot on the bottom of the fruit that grows and turns black ^[17].

Likely causes: Too little calcium reaching the growing fruit, most often because soil moisture swings between wet and dry. Low soil calcium, damaged roots, or some fertilizers can add to it ^[17].

What to do: Keep soil evenly moist with mulch and steady watering, and pick off affected fruit. Test the soil, and add lime only if the test calls for it ^[17].

When to ask an expert: If most fruit is affected despite even watering. Your county extension office can arrange a soil test for calcium and pH.

Cracked fruit

What it looks like: Splits that run out from the stem or circle around it. Rot can get in through the cracks ^[17].

Likely causes: Fast growth during ripening, usually after a dry spell followed by heavy rain or watering ^[17].

What to do: Keep moisture even and mulch the soil. Pick more often during rainy spells ^[21], and use cracked fruit soon. Some varieties resist cracking ^[17].

When to ask an expert: If fruit keeps rotting on the plant before you can pick it.

Fruit stays green or turns orange instead of red

What it looks like: Full-size fruit sits green for weeks, or colors yellow-orange and uneven.

Likely causes: Temperatures outside the best ripening range of about 68–77°F. Heat above about 85°F blocks red pigment, and cool weather slows ripening ^[12][5]. Fruit that has been chilled can color unevenly ^[10].

What to do: In hot spells, pick at first blush and finish ripening indoors ^[6]. In fall, pick fruit that shows color, and full-size green fruit, before nights turn cold ^[9].

When to ask an expert: If fruit colors unevenly in mild weather. Send a photo to your county extension office.

Spots on the lower leaves

What it looks like: Brown spots with ringed, target-like centers (early blight), or many small spots with dark edges and pale centers (Septoria leaf spot). Both start on older, lower leaves, which turn yellow and drop ^[17].

Likely causes: Fungi that survive on old plant debris and spread in warm, wet, or humid weather ^[17][21].

What to do: Remove badly spotted lower leaves. Water the soil rather than the leaves, mulch, space plants for airflow, and move tomatoes to a new spot each year. Clear out old plants at the end of the season ^[17].

When to ask an expert: If dark, water-soaked patches spread fast in cool, wet weather, or leaves show white mold underneath. That pattern fits late blight, which can strip a plant of leaves within about two weeks ^[17]. Contact your county extension office.

Related plants

Eggplant, tomatillo, and ground cherry are close relatives of tomato, and peppers belong to the same family. Tomatillo grows its fruit inside a papery husk, and ground cherry is a smaller husk-covered fruit. Like tomatoes, all of them are damaged by frost. Because relatives share soil-borne diseases, Texas A&M suggests not planting tomatoes or their relatives (peppers, potatoes, and eggplant) in the same spot more than once every four years ^[6].