The leaves on my tomato plants are darkening and yellowing

by Sal
(Oslo, Norway)

Q. We leave in Norway and are having a bit of trouble with our Tiger tomato plants. They were grown from seeds and are currently outside on the patio (looking out south-south-west). They are getting plenty of sun and warmth but the plants are just not happy at the moment and I am wondering if it's a combination of things. I read on your website (wonderful reference to us thank you!) something about purpling veins and a lack of phosphorus ... this could very well be one of the problems since I haven't fertilized (the compost I have used was supposed to slow release the fertilizer). I don't think it's a fungus disease, because it's not spots we're looking at (see pictures).

Actually I'm having trouble figuring out if I'm under-watering or over-watering. I read that "at the height of summer" the plants should be watered 2-3 times a week. The last couple of weeks we have been watering them 0.75 to 1 quart of water every other day. Are they rotting?

I have loved and nurtured my plants from seeds to grown plants, please help!

Q. Three elements may be contributing to your tomato plants' struggles with purpling on leaves.

  1. Cool temperatures. Even though your plants are receiving sun, daily temperatures with the highs in 60s are on the low side for tomatoes. They prefer temperatures between 70-85 degrees Fahrenheit.
  2. Phosphorus deficiency. Cool temperatures prohibit phosphorus uptake, which adds to purple coloration. Phosphorus is necessary for tomato plants to blossom.
  3. Over-watering. Excess water clogs, or even "drowns," tomato roots. Nutrients cannot pass through the soil.

Make sure your plants are getting as much warmth as possible. If nights (or even days) are cool, move the pot into a garage or protected area. Fertilize with a balanced tomato fertilizer, such as
Miracle Gro Tomatoes
or Tomato Tone. Check the soil regularly simply by inserting a finger. If it remains moist about 1-2 inches beneath the soil, then plants have plenty of water for that day.

Good luck and happy gardening!
Your friends at Tomato Dirt

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