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Can I prune tomato starts?

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  • Can I prune tomato starts?

    I started tomatoes indoors as I normally do, but this year I kept them on heat mats longer, and fed the plants with diluted fish emulsion on a regular basis. This was all an experiment to see if that's good or bad for starting indoors. The plants were extremely healthy and looking great, but now they're huge! They have exceeded the height of my grow lights and are stretching up above them now. The tops are leggy and reaching for light (in my basement), but the lower portions still look good. Can I prune the tops to be under the lights? That would mean cutting the main stem anywhere from several inches to more than a foot on some of the plants. They're way to big for Wall-o-Waters when I go to transplant them, which will not be good in my harsh Colorado climate. I still have another week or two until I'm safe enough from frost to transplant.

    Also, anyone know why they shot up so vigorously? Was it from the fertilizer encouraging growth?

  • #2
    I would expect its the ideal environment you created with the heat plus regularly feeding them. I use fish emulsion on my seedlings but I cut it back and dilute it more than necessary. Ive never done heat mats, but I have a friend who uses them alone without fertilizing and her plants get huge too, she plants under row covers and plastic when they are really big. Good Luck


    • #3
      I wound up trimming the tops. As a result, they are putting more energy to the lower growth as I suspected. They're sending out a lot of suckers which isn't great. We'll see how it goes.


      • #4
        What type of light?

        What type of light(s) were you using for your tomato starts/seedlings?

        In my experience, if the topmost portion of tomato growth was stretched and leggy, the most-likely cause would be that the light wasn't adequate enough to produce compact, stocky growth.


        • #5
          4' dual bulb fluorescent fixtures, with standard bulbs, not grow bulbs. I have three fixtures all giving light to the plants, so I don't think I have a lack of light. Plus, I didn't have this issue last year, but last year I started a little later, didn't fertilize as much, and didn't keep the heat mats on for very long.


          • #6
            Well, fluorescent bulbs aren't necessarily the best lighting for the setup you described. Sure, you didn't have the stretching issue last year, as you already stated you didn't fertilize as much, started later, and used the heat mats less. So you increased those three factors while holding the lighting constant (I'm just assuming).

            I start seedlings under T5 fluorescent grow bulbs and increase the lighting from 400W-1000W Metal Halide bulbs before transplanting to my greenhouse, otherwise I get stretched plants.