How to grow tomatoes

This single fact governs pruning, support, spacing and when the plant stops, and it is the reason tomato advice appears to contradict itself everywhere you look.

An indeterminate tomato is a vine. It grows from its tip indefinitely, flowers and fruits continuously along the way, and will keep going until frost kills it. Most heirlooms and most cherry tomatoes are indeterminate. These are the plants that want a tall stake or string, want their side shoots removed, and want their growing tip pinched out about a month before your first frost so the plant ripens what it has instead of starting more.

A determinate tomato is a bush. It grows to a genetically fixed size, sets its fruit over a short period, ripens it and is done. Most paste and canning varieties are determinate. These want a cage rather than a stake, and, this is the important part, you must not remove their side shoots, because those side shoots are where a large part of the crop is. Pruning a determinate tomato is straightforwardly destroying your own harvest.

Seed packets often bury this in small print or omit it. If yours does not say, the shape of the description tells you: anything promising a concentrated harvest for canning is determinate, anything promising fruit all season is not.

Sow indoors about six weeks before your last frost. Earlier is not better, a tomato started in January sits in a pot getting leggy while a February sowing catches up and passes it, because light rather than time is what a seedling is short of on a windowsill.

Our calendar sets plants out about two weeks after the last frost, and that gap is the single most useful number on this page. Frost kills a tomato, but cold merely stalls it, and stalling is what costs you the crop. Nights below about 50°F check a transplant so thoroughly that a plant set out two weeks later routinely overtakes it. In the maritime Northwest, where May nights are reliably cool, this is the difference between tomatoes in August and tomatoes in October.

Harden plants off properly over a week, an hour or two outside on the first day, building up. A plant moved straight from a windowsill to full sun scorches, and it never quite forgives you.

One more thing worth doing: brush your hand across the seedlings once a day, or put a fan on them. Mechanical movement produces shorter, thicker, sturdier stems, which is the difference between a plant that stands up when it goes out and one that flops.

Tomatoes are one of very few plants that root from their stems. Any part of the stem buried will grow roots, so a transplant set deep builds a far larger root system than one set at the depth it grew in the pot.

Strip the lower leaves and bury two thirds of the plant. If it is leggy, do not fight it, lay it down instead. The 1912 manual describes the technique exactly: dig a shallow trench three or four inches deep, sloping up to the surface, lay the bare stem along it with the root at the deep end, cover the stem along its length and firm it. The plant turns its tip upward within a couple of days and roots along the whole buried length.

That trench method is still the standard fix for a stretched transplant, and it is better than burying the plant upright, because the buried stem then sits in warm topsoil rather than cold subsoil.

Spacing depends on habit and support. Our calendar gives 24 inches in rows 36 apart, which suits staked indeterminates. The 1912 table's figure for staked plants, 18 inches to 2 feet apart in rows three and a half to four feet, is essentially the same answer. Unstaked sprawling plants need about four feet each way, which is what Burr specifies in 1863 and what Solomon still recommends for dry gardening.

Almost every tomato fruit disorder is a watering-pattern problem rather than a disease, and knowing that saves a lot of pointless spraying.

Blossom end rot, the sunken black patch on the bottom of the fruit, is a calcium delivery failure, not a calcium shortage. The soil almost always has enough; what fails is the plant's ability to move it to the fastest-growing tissue, and that failure is caused by irregular water. Adding calcium to the soil is the standard advice and it is usually treating the wrong thing. Water evenly, mulch, and it stops.

Splitting and concentric cracking around the shoulders is the same mechanism from the other side: a fruit that slowed in drought and then got a heavy soaking expands faster than its skin can stretch.

So: water deeply and regularly rather than lightly and erratically, and mulch to buffer the swings. Container plants need far more attention than ground ones because there is no buffer at all.

Once fruit is ripening, easing off slightly concentrates flavour, but easing off is not the same as letting the plant dry out and then rescuing it, which is how you get the split fruit you were trying to avoid.

Late blight is the disease that ends tomato crops here, and it is worth understanding rather than fearing. It is a water mould, it arrives on airborne spores, and it needs prolonged leaf wetness with mild temperatures, which is a precise description of a Pacific Northwest September. Brown-black patches spread on leaves and stems, fruit develops firm brown blotches, and a plant can go from healthy to finished in under a week.

You cannot prevent the spores arriving. What you can do is make the conditions worse for them: space plants for airflow, water at the base rather than overhead, remove the lowest leaves so nothing touches the soil, and grow under cover if you can, a simple rain shelter over a tomato row is the single most effective anti-blight measure available to a home grower, because it keeps the foliage dry.

Choose early varieties. A tomato that ripens in sixty days from transplanting may be finished before blight weather arrives; one that needs eighty-five may not be. In a cool maritime summer this is a bigger lever than anything else on this list.

Early blight is a different and less dramatic disease, brown target-ringed spots working up from the lowest leaves. Remove affected leaves, mulch to stop soil splashing up, and rotate.

Blight-affected material should not be composted, and neither should potato volunteers, which host the same organism.

About four weeks before your first expected frost, stop the plant making new work. Pinch the growing tip out of every indeterminate, remove any flowers and any fruit too small to have a chance, and the plant redirects everything into ripening what is left. It feels wasteful and it converts a mass of green fruit into an actual harvest.

Tomatoes ripen on stored sugars, not on sunlight, so removing leaves to expose fruit to the sun does nothing useful and risks sunscald. Leaves feed the plant; leave them.

Temperature, not light, is what ripens them, and above about 85°F the pigment that turns them red simply stops being produced, which is why tomatoes in a hot spell go yellowish-orange and stall.

At the end of the season, pick everything and ripen indoors. Any tomato that has reached full size and gone from hard green to slightly paler will ripen off the plant. A brown paper bag with a banana in it works because the banana gives off ethylene. Whole trusses hung upside down in a shed work too. What does not work is a sunny windowsill, which cooks them.