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Some Like it Hot; Tomatoes Do NOT!

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
Answer. You heard incorrectly, Charlotte, apparently transposing two of my standard tomato warnings. Tomatoes should not be WATERED in the evening, as their leaves staying wet overnight can cause disease. No plants should have their leaves wet deliberately in the evening, especially disease-prone ones like tomatoes, roses, and lilacs.

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
Answer. Albuquerque? How hot is it down there?


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