Do I need to fertilize if I'm using ProMix?

bananastandMarch 29, 2014

I finally got a grow light arrangement and started my first flats of seedlings this spring. I have a few cells that still need to germinate, but also some happy baby plants. I started things on March 18. Questions from a newbie...

The FAQ says you should start fertilizing with a dilute (25% strength) liquid fertilizer once a few true leaves form. Is that necessary with a seed starting media like ProMix, which contains compost?

Also, this is unrelated to fertilizer, but I see that I have a couple little gnats flying around my plants. I suspect they are a side product of what were too-damp conditions when I started the seeds. As soon as I realized I had a problem, I took the plastic domes off of my flats, even though I still had a few ungerminated cells. Instead I and am closely watching the moisture so nothing dries out. This has already helped-- there was a bit of algae beginning to grow on my shallot cells (which take a while to germinate) but now that the cover is off, not only have the shallots emerged but the algae is gone. But I'm wondering if I should be worried about those gnats? There aren't many. I've seen maybe 2-3 of them.


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

Is that necessary with a seed starting media like ProMix, which contains compost?

Since when does ProMix contain compost? Mycorrhizae, what is added to ProMix, is not compost.

But ys, you need to feed the plants when using ProMix. Do so using 1/4-1/2 strength diluted liquid fertilizer of your choice weekly.


    Bookmark   March 29, 2014 at 7:11PM
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I have something called ProMix Ultimate Organic Mix. Here are the ingredients:

Ingredients: Canadian Sphagnum Peat Moss, Sea-based Compost, Limestone, Perlite, and Mycorise.

    Bookmark   March 31, 2014 at 2:05PM
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ZachS. z5 Littleton, CO

As far as your gnats go, in some cases they are present in bagged soils and mixes. If they are, keeping an overly wet environment only exacerbates the problem, as well inviting the problem in and of itself.

With regards to domes and the like, once you see sprouting, they need to go. It doesn't matter if 60% of the seeds have not sprouted, with the domes on, you are only asking for problems for the ones that have. If you have all the same seeds under the same dome, chances are once one sprouts, the rest are very soon to follow, and in fact have likely germinated beneath the soil, they just haven't sprouted aboveground yet.

    Bookmark   March 31, 2014 at 3:43PM
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My domes are off and have been off for about 5 days... the gnats persist. Could they have something to do with the little bit of algae that still remains on the surface of my shallot seedlings? Yesterday I sprayed the surface with a very dilute solution of water and hydrogen peroxide (1.5 tsp to 1 c) because I read that it can help with algae.

    Bookmark   March 31, 2014 at 5:26PM
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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

Hi Lucille - I have no experience with that particular mix but I would suggest feeding with a mild diluted liquid fertilizer anyway. Even if the mycor can derive some nutrients from the compost for the plants an additional supplement would be very beneficial.

The fungus gnats, like the algae, usually indicate too much watering or too much water retention. I don't know how well this type of mix will drain compared to regular ProMix. Compost mixes often don't drain well. But you can get rid of the gnats with the Btk in Mosquito Dunks. That is what most use for the problem.


    Bookmark   March 31, 2014 at 6:20PM
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SouthCountryGuy Zone 4b-5 SE BC(Zone 4b-5 SE BC Canada)

+1 digdirt.

and i am not afraid to dr. doom indoors.


    Bookmark   April 1, 2014 at 1:29AM
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The only liquid fertilizer I have is the Alaska fish concentrate stuff, which I prefer not to use in the house since it smells oh so fishy, even when diluted.... any advice/input on other good liquid fertilizers to try?

    Bookmark   April 1, 2014 at 11:48AM
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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

Well diluted Miracle Grow and similar are probably the most commonly ones used by far. Do you only want organic ones?

Most organics are going to have some odor, it is the nature of organic fertilizers - they smell. So organic gardening outside is great, inside not so much because of their slow effects, need for active soil bacteria to even work, and odor.

Other than worm tea if one has a vermicomposting setup, IMO the best organics for using indoors are one of the many fish/kelp blends available. Not only are they better balanced, offer a wider range of nutrients, but the kelp reduces the odor of the fish somewhat. It isn't odor free but better and unfortunately the smell is the most notable price we pay if we insist on only using organic fertilizers for seedlings.


    Bookmark   April 1, 2014 at 1:02PM
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Hmmm, thought that might be the case. Thanks! I guess I feel better about tolerating a little fish smell more so than going chemical.

    Bookmark   April 1, 2014 at 9:54PM
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I dont understand why people are so adamant about "chemical" fertilizers. Its true that over using them in your garden can screw things up. But using them in container plants only makes sense. Container plants generally don't have all of the soil bacteria that is needed to break down the organic ferts. I understand not wanting to use chemical pesticides, but chemical fertilizers are not "bad" for you. Think of it as similar to giving your kids Flintstone vitamins until they are old enough to be willing to eat broccoli.

I use organics in my garden, and "chemical" ferts in anything that is in a pot.

    Bookmark   April 2, 2014 at 7:18AM
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Mandolls, I know what you're saying. For me it's more so not wanting to support a corporation like Scott's that has done so much environmental harm. I don't want to get into an argument, it's just how I do things! I know others have a different way, and that's totally fine.

Thanks for all the advice everyone!

    Bookmark   April 2, 2014 at 10:21AM
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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

For those interested there are lots of other choices out there besides anything from Scotts/MG.


    Bookmark   April 2, 2014 at 11:06AM
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yep - I do my best to avoid any MG/ Scotts products for the same reasons, so I am with you there.

I tried the Dyna-Grow Fish /Kelp fert that I use in the garden on my indoor seedlings once - nothing quite like walking into a warm humid fishy smelling space - took a week for the smell to dissipate.

    Bookmark   April 3, 2014 at 7:21AM
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