I have a seed starter kit with a wicking system. The kit came with a peat moss mix and I have purchased some new peat moss pellets for starting seeds. I know that peat does not really contain any nutrients for the plants. If I am simply using a typical liquid plant food as fertilizer, is that good enough for a month or two of growing? Do I need to transplant quicker to larger pots with more nutrient rich medium? Would using a hydroponic fertilizer, which contains much more trace elements/minerals, be a better option?

2 Answers 2


You don't need any fertiliser at all to start with - the clue is in the word 'starter'. You're only meant to germinate the seeds, then wait till they have 2/3 sets of leaves (one cotyledon pair and one true leaves), at which point you move them into individual pots containing probably seed and cutting compost - then move them up into potting compost in bigger pots. Seed and cutting compost has a very small amount of nutrition, ordinary potting compost a bit more, and as the plants get larger, that's the time to start fertilising.


It's not about how long you can keep them in the starter trays, it's all about how many leaves they've got. Once they've got no more than 3 sets of leaves, they must be moved to something larger for root development. Germination to seedling stage varies according to light levels and warmth, so it may be as short as 10 days, or as long as a month.

  • So how long can I keep them in starter medium in the starter trays? Two months?
    – Evil Elf
    Feb 24, 2015 at 14:59
  • @EvilElf - see updated answer
    – Bamboo
    Feb 24, 2015 at 15:09
  • I see starter flats at the garden centers with pretty mature plants. Are they able to keep them in the trays because of more nutrient-rich growing medium? I would hate to have to go to an intermediate pot instead of from seed starter to the garden after the last frost.
    – Evil Elf
    Feb 24, 2015 at 15:47
  • @EvilElf - terminology's different here - starter flats? I guess that might mean what we call plug trays, and if it does, the 'plugs' in the tray vary in size from egg cup equivalent to, say, a small teacup. Good sized plants sold at the store in plug trays are usually in the teacup sized ones, sometimes in the smaller ones, which means the smaller ones don't develop such good roots. Are we talking about the same thing when you say starter flats and I say plug trays? Most of these plants will have been started off in seed trays and transferred to the larger plug trays in better compost.
    – Bamboo
    Feb 24, 2015 at 15:54
  • The tray I have has the smaller plug sizes. So, I really need to start in a bigger size plug, or transfer the seedlings to bigger pots before taking them to the garden?
    – Evil Elf
    Feb 24, 2015 at 16:18

The first leaves of the seedlings (not the true leaves) contain nourishment for the plant. I suppose that's one reason people say not to fertilize seedlings. Another reason is likely that seedlings may not be strong enough to take the nitrogen from most fertilizers, which can burn the leaves (and in the case of seedlings, kill them more easily). However, not all fertilizers are so dangerous to seedlings, but if you just grab a random fertilizer without investigating its npk values, it will probably be bad. True, you don't really need to use fertilizers at all, but you can use some of them safely on seedlings.

Here's what I liked to use with indoor plants under grow lights, started in 20 ounce foam cups in 2015, and it worked pretty well for tomato and pepper seedlings:

  • 8 quarts new seed-starting mix (Nature's Seedling Mix)
  • 2 tablespoons of 7-7-7 fertilizer (Greenview All Purpose Plant Food; bar code: 088685310744)
  • 2 tablespoons of basalt rockdust (from rockdustlocal.com); for added minerals, like calcium and silica

I mix it all together and put it in my containers (and plant the seeds). I don't fertilize them again unless they ask for it (show signs of needing it). The rockdust and 7-7-7 fertilizer seem to help the plants quite a bit, and they don't seem to hurt them.

I use 7-7-7 fertilizer because it's an even one that won't burn the plants or do anything particularly dangerous to them (some even fertilizers, or even low nitrogen fertilizers actually can burn plants, however, but mine didn't; I'm not sure if their NPK values are accurate). I used basalt rockdust because I didn't trust the seed-starting mix to have enough of the right minerals for strong plants. I imagine the same is true for peat moss. True, you don't need rockdust, but my plants enjoyed it, seedlings and otherwise.

I think the main problem with peat moss would be if it's infested with something. You can grow plants in peat moss just fine, but it may or may not be the best solution for your situation.

It should be noted that peat moss has a PH of about 4.0. That's highly acidic. Tomatoes are said to prefer a PH of about 6.0 to 6.8. So, adding some such as rockdust (which is high in calcium) should raise the PH.

In 2016, I used a mixture of mostly worm castings with some peat moss for my seed-starting mix, this year, with no rockdust or fertilizer added (in an unheated, outdoor greenhouse, in full sun, this time). It worked well for the vast majority of the plants. Worm castings are supposed to be at least a little on the alkaline side. The greenhouse plants only complained for fertilizer (for phosphorus, in particular) after they were sufficiently large, of course, but after a foliar spray of monopotassium phosphate, they perked right up again (and are still fine weeks later). They haven't been transplanted to larger pots (they're going directly in the garden), and they're still growing fine. These are in seed trays with larger than average cells, but they're still normal seed trays (they're not huge).


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