Tomato

Start tomato seeds indoors, five to six weeks before you plant out

Sow into moist seed-starting mix about a quarter inch deep and keep the flat warm and under strong light. Count back five to six weeks from the date you can safely plant out — which is after your last frost AND once soil is above 60F — not from the last frost date itself and not from any fixed calendar date. Tomatoes need a long warm season to set and ripen fruit, but a seedling held indoors too long gets leggy and root-bound and sulks for weeks after planting. Five to six weeks produces a stocky plant that keeps growing the day it goes in the ground.

Plant out once frost is past and the soil is above 60F

Harden seedlings off first by setting them outside in wind shelter and partial sun, adding exposure over a week or two and bringing them in if nights approach freezing. Then plant deep, burying the stem up to just below the lowest leaves, or lay the seedling in a three to four inch trench with only the top leaves out. Set them out in late afternoon or on a cool, cloudy, calm day. Tomato stems grow roots anywhere they touch soil, so a buried stem becomes a bigger root system and a more drought-steady plant. Cold soil below 60F stalls root growth even when the air feels warm, which is why a plant set out too early is often overtaken by one planted two weeks later.

Water deeply and infrequently to head off blossom end rot

Apply one to two inches per week as one or two deep soakings rather than daily sprinkles, and count rainfall toward it. Water at the base and keep the foliage dry. Do not let plants go into the night water-stressed. Blossom end rot is not a disease and usually not a soil calcium shortage. Calcium rides into the fruit on the water the plant takes up, so a plant swinging between bone dry and soaked cannot deliver it to the fruit tip no matter how much calcium sits in the soil. Steady moisture is the fix, not a calcium spray.

Mulch once the soil has warmed, not before

Lay organic mulch around the plants after the soil has warmed past about 75F, or use black plastic from the start if you want to warm the soil instead. Apply herbicide-free grass clippings or straw three to four inches deep. Keep it pulled back an inch or so from the stems, and do not pile it so deep that the soil stays sodden. Early blight and Septoria spores overwinter in last year's debris in the soil and reach the plant when rain splashes soil onto the lowest leaves. A mulch layer is a physical lid on that splash. It also buffers soil moisture, which is the real lever on blossom end rot, since calcium only moves into young fruit when moisture is steady. Applied before the soil warms, though, mulch works against you — it locks the cold in.

Side-dress when the first fruits start to enlarge

Wait until the first fruits are visibly swelling, then scatter fertilizer alongside the row and water it in: about half a cup of 46-0-0, or one cup of 27-3-3, or three and a half cups of 10-3-1 per 100 feet of row. For a handful of plants, USU's rate is about half a tablespoon of 21-0-0 per plant at four and eight weeks after transplanting. Fruit enlargement is when demand outruns what the soil is supplying. Feeding nitrogen earlier than this buys you a tall leafy plant that flowers late and sets less, because the plant spends the nitrogen on vegetative growth while conditions are still easy.

Pull and destroy the vines when the season ends

Pull the plants roots and all and bury or burn them where local rules allow, rather than leaving them standing. If any plant showed late blight, bag it and bin it. Pull volunteer tomato seedlings next spring too, and do not plant tomatoes, potatoes, peppers or eggplant on that ground for three or four years. Early blight and Septoria overwinter in the debris you leave behind, so this season's dead vines are next season's first infection. Late blight is the sharper case: it does not survive on dead tissue but rides through winter in living tissue like cull potatoes and volunteer seedlings, which is why those plants get bagged and not composted. A home compost pile rarely gets hot enough to kill either.

⚠ Do not compost late-blight-infected plants. Bag them and dispose of them in the trash.

Scout tomatoes for hornwormJun – Aug

Check at dusk for dark frass and stripped stems; hand-pick the caterpillars. Early removal saves the plant; Bt works if numerous.

Early blight and Septoria: start chlorothalonil as the canopy closes

Begin spraying chlorothalonil, or a copper product if you garden organically, as the plants get big enough to shade their own lower leaves, and before you see spots. Repeat on a 7 to 14 day interval through the rest of the season, covering the undersides of the lower leaves. Stake or cage the plants and strip the lowest leaves as they go so air moves through. Alternaria solani and Septoria survive in last season's debris and infect the bottom leaves first, then climb. Both need long hours of leaf wetness, which is exactly what a closing canopy creates by trapping humidity. Once the target-ringed spots are visible the spore load is already in the planting, and a fungicide that only protects healthy tissue can no longer catch up.

⚠ Chlorothalonil on tomato carries a 0-day pre-harvest interval, so fruit can be picked the day of spraying, but wash it. It is a protectant only and will not cure existing lesions. It is highly toxic to fish and aquatic life, so keep it out of ponds and storm drains, and follow the label rate.

Pick fully colored but still firm

A tomato takes about 25 to 35 days to go from open flower to ripe, faster in heat and slower in cool weather, so start checking a month after bloom. Pick when the color is full but the fruit is still firm. Ripen anything you pick early indoors at room temperature, laid one layer deep and not touching. Fruit picked at full color has already received everything the plant will send it, and waiting for softness on the vine mostly buys splitting and pest damage. Ripening runs on warmth, not light, so a sunny windowsill is no better than a warm counter and often cooks the fruit instead.