My Tomato Seedlings Have Purple Stems (Is that Normal?): My Organic Garden Mishap #2

So, the only thing that seemed to grow well in my old seed starting tray this year were my tomatoes. Specifically, the 4 Break O’Day tomatoes and 9 Tess’s Land Currant Tomatoes that were planted about 4 weeks ago (there was supposed to be 12, check out my heat mat experiment to see how much better my 2nd batch germinated in it). These were planted about 2.5 weeks ago on a heat mat…Unfortunately both batches stems are turning purple…

I stopped by my new favorite store Brew & Grow today and asked them why the stems were purple and it if was bad – they said yes and said I need some fertilizer so they sold me this…. WRONG

WRONG… I posted that twice because I didn’t want you to stop reading at that point, run out and buy fertilizer and kill something because after browsing through multiple other organic gardening forums I learned that my purple stems are quite a common phenomenon AND I shouldn’t necessarily be fertilizing yet.

So What Should I do About Purple Stems? 

Information on the internet is completely fragmented and there seems to be a lot of gray area. Based on the information, purple stems may or may not mean that your seedlings are under stress. It generally depends on a few factors, be sure to take into consideration the age of your seedlings to help you determine what your little babies need.

Last year, I had the purple stem issue at a really young age – at the cotyledon stage when the plants were only about 1.5″ tall. I kept them watered and under my grow light in the same seed starting container they were started in for about a month. They didn’t continue to grow and never developed their first set of true leaves. This set me WAY behind on my garden, I think so far behind that I didn’t get much fruit this year.  I transplanted them a little too late into pots and they started to grow a bit but not very fast and the purple stems didn’t go away. Here’s my observations…. personal and semi-professional (if you can call the forum contributors professional gardeners)

Purple Stems When Seedlings are Infants, no true leaves, only Cotyledons, (the first set of “embryonic leaves”): Like I said, I think if there are multiple reasons so try and evaluate your situation. These plants are in this stage…

1. The plants are stressed because of close quarters – they could be stressed because they are planted to shallow or too close together. I think this was my problem last year. When the plants are in too small of a cell they have trouble growing and become stressed. My plants completely stopped growing, once they were transplanted, they continued growing. Solution: Transplant so they have more space.

2. The plants are cold – if you think that they’re appropriately planted, it could just mean that they’re too cold. Solution: Not to worry, apparently the purple stems will go away once it warms up a bit.

When the seedlings are new, they have 1 or 2 true sets of leaves: These seedlings were planted about a month ago. They have just started to develop their second set of true leaves. Why are the stems purple?

1. The plants are stressed because of close quarters (I will be transplanting these soon – see my post when to transplant tomato seedlings into pots to learn why)

2. The plants are cold – if you think that they’re appropriately planted, it could just mean that they’re too cold. Not to worry, apparently the purple stems will go away once it warms up a bit.

3. The plants don’t have the nutrients they need, specifically Phosphorus – I start all of my plants in a soil less mix that has absolutely no fertilizer. If you are using a seed starting mix that already has fertilizer in it, this shouldn’t be your problem. If you’re using a soil less mix, you can start lightly fertilizing after the plants have their first set of true leaves. DO NOT OVER FERTILIZE! Be sure to use fertilizer that is high in Phosphorus, specifically one that has a 1-2-1 NPK ratio.

For me, I think a combination of close quarters and no nutrients are causing the problem. My seedlings haven’t halted their growth yet but I’m not going to wait a month to find that out and set my garden back again this year. Later today I’ll be transplanting my tomato plants in the seed starters into pots. Check out this post to figure out if it’s time for you to do it too!

Do you have any success/horror stories about your tomato seedlings? I would love any feedback on purple stems, fertilizing, or other mishaps!