Some Like it Hot; Tomatoes Do NOT!
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Question. When it comes to sun, where should I place my tomato plants? I thought I heard you say that tomatoes should not get full sun in the afternoon because the heat would cause moisture overnight that would lead to disease. Did I hear you correctly? Thanks,
- ---Charlotte in Leesburg, VA
In an emergency, you can safely water plants at their base in the evening; just be careful not to wet their leaves. But morning is always the best time to water. You can even safely wet plant leaves in the am if the sun will soon dry them off.
Your full sun in the afternoon may simply be too much sun for tomatoes in hot areas of the country and/or during the kind of heat waves the East Coast has been having this year. We tend to think of tomatoes as THE classic plants of summer, but most varieties suffer when daytime temps stay above 90° F. or nights don't drop below 75° F.
Now, these extremes won't kill the plants, but they will destroy the current crop of pollen on the flowers. Let's say it's a searing 97° F. every day for a solid week; no flowers that open during that stretch will produce tomatoes. But existing tomatoes should be fine, and new flowers that open under normal temps should produce normal pollen and normal tomatoes.
That's what can make a seemingly simple seed catalog phrase like "full sun" so treacherous. Plants so indicated do generally need full, all-day sun in the Northern tier of the country, but as you move into my Southern Pennsylvania down to around DC it really depends on the season. Last year was cool and cloudy and the plants craved as much sun as their little solar collecting leaves could gather. But THIS year, we've already had several stretches of pollen-frying weather, and so this season's plants would prefer to get some shade after one or two in the afternoon. And down in the torrid Deep South, "full sun" almost always means, "give these poor things some afternoon shade—please!"
And I mean afternoon shade, not morning shade followed by sun. No matter where they live, tomatoes, roses and other disease prone plants always want morning sun; the sooner the sun strikes their leaves in the am, the faster the dew will evaporate and the healthier the plants will be.
Question. Mike: I started some heirloom tomatoes from seed. They are beautiful, green and vigorous but sadly not too much in the way of tomatoes. I have been feeding them Miracle Grow tomato food every week to ten days. How can I get my plants to flower and fruit?
- ---Lorette in Albuquerque, New Mexico
Question. Lorette responds: "June can be very warm and sunny, with daytime temps reaching the high 90s. But the nights are often still in the 50s, which makes the plants slow to take off. Summers are often torrid.
Answer. Well, as you have probably surmised by now, you live in a challenging climate for summer tomato growing. First, ditch that artificial plant food; those chemical salts are especially nasty in hot weather, when they make it difficult for the plants to take up water efficiently.
In seasons to come, you'll also want to plant your tomatoes especially deep, so that their roots can reach down into the coolest part of your soil. Give them a thin mulch of compost at planting time, but leave the ground otherwise un-mulched early on to allow it to warm up quickly. Then mulch with a couple cooling inches of compost or shredded leaves when hot weather arrives.
And your plants need some afternoon shade. Yes, they could benefit from full sun early in the season, but afternoon shade is going to be essential from mid-June on. So if they're in a spot that gets blasted all day, see if you can rig up some retractable shade cloth; or use a beach umbrella to shade them after 2 pm on really blistering days.
You may also want to choose varieties that set fruit more reliably in hot weather. All cherry tomatoes are good at this (in general, the smaller the tomato, the hotter the weather their pollen can survive), as are varieties with names that conjure warmth, like Solar Set, Surefire, & Heatwave. And, weirdly, some tomatoes bred for cool, short-season climes—like Santiam, Oregon Spring and Oregon Star—also do well in hot areas, thanks to their ability to set fruit without pollen (known as "parthenocarpic").
And finally, work the season you have, not the one you'd like to have. Gardeners in your Deep, Deep South grow their best tomatoes early and late, avoiding July and August the way I do December and January.
Set some plants out as early in the season as you can, and keep them warm at night with row covers or the famous Wall o' Water or similar device that uses water-filled chambers to store daytime heat and keep the plants cozy at night.
Then just be happy if you can keep them shaded, watered and alive when local dogs start living under the porch.
And then extend their season deep into the late fall with the same tactics as early Spring. Your late crops might be the best of all, as the soil will already be warm and the plants will be aching to produce!