Potting up: when and into what

Brett-CpGMarch 20, 2012

I have some two week old seedlings that are kicking butt right now, and was wondering the best time to pot up, and what medium to move them to. They are currently in seed starter mix (coco fiber), and many of them have 1-2" long true leaves already (one has actually begun its 2nd set of true leaves, which blows my mind a little bit for only 2 weeks). They're in perforated 6 oz styrofoam cups currently (1 each), so they have a little room to grow. Most of the commercial potting mixes seem to be high nitrogen (12-6-6 or 10-5-5)...which when it comes to tomatoes doesn't seem right, but then I wondered if early on the nitrogen would suit them well until they get big enough to make fruits. I'm really tempted to just make my own mix of perlite, peat moss, and the 10-5-5 potting soil...but before I go down that path, I thought I'd get some ideas.

What are some of your opinions on when to pot up, and what medium you use? Or do I even need to pot up (hoping to transplant in 3 weeks or so), considering the 6 oz cup is bigger than most cells I'd buy at the local Lowes or Home Depot.

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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

You can pot-up at any time. I often do them at the cotyledon stage, others wait for the first set of true leaves to develop. Into what - any of the good soil-less growing mixes available. Some contain a small amount of fertilizer, some don't. Some swear by Miracle Grow Potting Mix, some hate it.

A popular one mentioned here often is ProMix BX, Sta-Green is another, Fos Farms is another brand. It all depends on what is available to you locally.


Here is a link that might be useful: brands of soilless potting mixes

    Bookmark   March 20, 2012 at 9:39PM
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Hmm...I suppose I need clarification. Is there a real difference between my seed starting mix and the different potting up mixes? I mean, one is coco-fiber (seed starter) but then you refer to "soil-less growing mix." Is that not the same as my seed starting mix?

    Bookmark   March 20, 2012 at 9:48PM
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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

No very different components. The soil-less potting mixes are made with peat, vermiculite, perlite, a low-dose nutrient charge of some type, and a wetting agent. Many also add bark fines to improve drainage and some include worm castings for further nutrients. Some also add beneficial bacteria to stimulate root development. All depends on the brand.

Coco coir is just that - shredded coconut fibers. No nutrient value and poorly draining. Ok for germination but provide nothing for growing on.


    Bookmark   March 20, 2012 at 10:00PM
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Looks like tomorrow or Thursday holds a trip to the hardware store then. I appreciate the input.

    Bookmark   March 20, 2012 at 10:25PM
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Brett - If they are already in 6" styrofoam cups, leave them alone until you're ready to put them in the garden.
John A

    Bookmark   March 21, 2012 at 10:42AM
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Yeah, what John A said. If the normal size drinking cup is full close to the top there is no reason to transplant. I have been using this method for several yrs with MG Seed starter with great results. Six to eight weeks after germination they are good to go...hardened off of course. I have 45 of them sitting on a chest of drawers under saran wrap as we type.

    Bookmark   March 21, 2012 at 12:43PM
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Unless you see roots growing out of the holes, leave them in the cups. They should be sufficient.

    Bookmark   March 21, 2012 at 2:36PM
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dickiefickle(5B Dousman,Wi.)

Brett what is 10-5-5 potting soil ?

    Bookmark   March 22, 2012 at 2:56AM
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Ohiofem(6a Ohio)

Tomato seedlings do benefit from being transplanted (potted up) at least once before planting out. This stimulates roots, especially if you plant them more deeply (up to the first set of true leaves). If you don't want to buy larger pots, you can use 16 ounce cups like they sell at fast food places or even cut off half gallon milk/juice cartoons, with drainage of course. At the rate they are growing, they could be 18 inches tall in another three weeks. Generally you want the soil to be made of larger particles than seedling mix, so it drains very well. I prefer a mix that doesn't have fertilizer or moisture control in it. You want to let it dry out more between waterings and you want to be able to feed it with a balanced fertilizer at half strength or less.

    Bookmark   March 22, 2012 at 9:53AM
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Right on Ohiofem. Also, Brett, don't worry about higher nitrogen on younger plants. 3-1-2 is best for vegetative growth, the time nitrogen is used the most. Once fruiting starts, reducing nitrogen input causes energy generated by existing leaves to support the fruit rather then more leaves.

    Bookmark   March 22, 2012 at 10:26AM
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