What’s wrong with my tomato plants

These have been looking good but the are leftovers and have been in these cups too long. Have been outside in the rains and storms and sunshine. New leaves are small and very dark green. Some are even purple on the back side. The ones I have already planted out are looking the same way. Planted from seed.

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Usually purple plant veins/stems is a symptom of phosphorus deficiency.


What to correct it?

Just researched and yep…the pictures match exactly. Our weather has been cool (for the season), very wet, and they are in a peat based potting mix. My soil pH runs 5.7. I’ve limed but only a few months ago. So they’ve got many of the risk factors. Thanks, Ben!

How long ago did you transplant? If only recently they’ll probably be fine after some adjustment time. You can always give a little fertilizer and see how they react. For the ones still in the pots, I would definitely give them a little fertilizer. I usually use a water soluble balanced fertilizer for tomatoes.

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You can also do a foliar nutrient spray for a faster fix. I usually do 1/4 strength of a liquid fertilizer and do 2-3 apps for a week or just until I start seeing an improvement.

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I used to start tomatoes early, but ran into this problem, and it’s mostly caused by the cold. They really do not like temps below 50. They do better with them in fall when mature plants. The purple is a sign of stress. Yes caused technically probably by a phosphorus deficiency but the real culprit is the temps… They should grow at that pH. So I start them later. What convinced me was one year needing to restart some plants, and in the long run the plants started a month later after 3 months were doing better than my earlier plants that had to endure the cold stress. It took it’s toll.

Currently my plants are about 3 inches tall started March 31st. They are still under lights, and have not been outside yet. I will put them out in 2 weeks.


Everything Drew said is true for me as well, and my plants are at the same stage as his.


We typically have our plants out by mid March. We’ve had unseaaonal wet cool weather and until last week had temps in the 40’s. We are now on track for 60’s-80’s which is more seasonal for us. So basically they should fix themselves? I had planned to spray soon with Miracle Grow so that will help i guess.

Yes they should but treat them with kid gloves, don’t under or over water.

As others said, this is mostly phosphorus deficiency but there is one leaf that shows signs of a fungal disease, possibly early blight. This usually shows as a leaf that twists and eventually develops a spot of dead tissue. It is best to remove affected leaves on small plants.

As for fertilizer, I’ve switched from miracle grow 15-30-15 to Expert Gardener 24-8-16 (available at Walmart) with micronutrients to use with seedlings in containers. Please be careful with this. 1/2 teaspoon is enough to fertilize a tray of 48 seedlings. Also, this is not very high in phosphorus so if your soil is deficient, a different fertilizer would be more beneficial.

I think Drew51 is probably right. Although purple foliage could certainly represent other problem issues, it’s also a classic symptom of phosphorus deficiency. Years ago when I would put tomato plants outside under row covers early in the spring, leaves would turn purple and plants would just sit there, not seem to grow.
Later I learned soil temp effects nutrient uptake availability and phosphorus is especially prone to becoming unavailable in a cold soil, especially to tender plants like tomatoes, even when present in sufficient quantity. Adding phosphorus to the ground won’t help if the ground is too cold.

Also, ph can play a role. Note on the chart how quickly phosphorus availability tapers off compared to the other two primary nutrients when soil ph becomes too acidic or alkaline.


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On side note of possible interest: Note iron, boron, copper & zinc availability in ph range which so called acid loving plants thrive in. This is why blueberries, azaleas, etc, when growing in soil too alkaline for their liking exhibit deficiencies in those nutrients. They may be present in sufficient quantities but soil ph renders them unavailable for uptake.

In case anyone’s interested, here’s some additional info from this Michigan State University article which explains a little bit about electrical charges of soil nutrients and why some nutrients resist leaching more than others, and why some nutrients (relative to others) are especially sensitive to soil ph.

Anions and Cations in Plants

From the article: _Since soils are negatively charged and plant nutrients are positive and negative, some nutrients are attracted to soil while others are not – the “opposites attract” principle. Those nutrients that exist as anions (-) are moved through soil, meaning growers need to be careful how they are applied regardless of soil type. These nutrients readily travel wherever water carries them, leading to nutrient runoff and leaching and economic loss and environmental concern.

Cations (+) are more readily bound to soil, resulting in these nutrients moving through the soil more slowly. _

This chart from the article demonstrates why iron, manganese, copper, boron & zinc are especially unavailable to acid loving plants growing in a soil of too high ph. These nutrients have a +2 charge.


This article also sheds light on phosphorus tie up in cold soils:
The odd anion is phosphorous. Even though it has a (-) charge, it is not mobile in soil because phosphorous forms are not very soluble.

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