Seedlings - To fertilize or not to fertilize?

tonybaloneyMarch 12, 2010

I've been reading a lot of books as well as posts on this forum. There are a lot of ideas about how to fertilize (or not fertilize) our tomato seedlings. One conclusion I've come to is that most of us *over*-fertilize our tomato plants. But there are so many different ideas about what to use, frequency, dilution ratio, etc.

Some say a very dilute solution of kelp or seaweed, or miracle grow. Some say the nutes in the mix are enough to carry a tomato through to transplant time.

One poster on here, digdirt, claims that it's unnecessary to fertilize seedlings at all until transplant time!

Here's a snip from one of his posts:

"Personally, while I add some compost to my mix for leafy greens and a few other veggies, I don't feed any of my tomato seedlings anything - ever - never have - until they go into the garden and then the planting holes get well-amended as they are planted. They get started and grow on in either Jiffy mix, Metro mix, or my homemade peat/vermiculite mix whichever I have available. Been doing it that way for over 40 years."

So what to do?

Here's one possible starting point: I think it's important to determine just how much "food" a plant is carrying with it, in seed form. A plant can't grow without nutrients. That's obvious. But all seeds carry a small packet of nutrients to jumpstart growth and sustain a seedling to a certain point in its journey. My question is, where is this point where a seedling has exhausted its supply and needs to obtain nutrients from the surrounding environment?

So let's solve this thing once and for all (yeah right.) I welcome anecdotal evidence but science and research on this subject would be great.

I look foward to ya'lls answers!

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See Elimination of the adverse effects of urea fertilizer on seed germination, seedling growth, and early plant growth in soil. As far as I know, the only complete fertilizers without urea are those formulated for hydroponic use. Personally, I find that 1 gram/gallon of urea is beneficial to seedlings when added to 5 grams/gallon hydroponic fertilizer.

    Bookmark   March 12, 2010 at 11:12AM
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We never fertilize seedling until we repot them from the 12oz starting cups to the 2 quart pots when they are then 8 to 12" high. I use 1/2 strength miracle grow at that time, one time. I do fertilize with manure and 10-10-10 in the hole when planting to the garden and then give each plant a watering of 1/2 quart or more or full strength miracle grow depending on how wet the soil is. The plants are 18 to 24" high at that time. Potting soil has enough nutrients to sustain plants for six months. Fertilizing seeding can damage or kill them and is totally unnecessary.

This post has some info on our tomatoes.

Here is a link that might be useful: Mom's Garden Pics

    Bookmark   March 12, 2010 at 12:12PM
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There's a guide I found on "that other forum" written by Carolyn about starting tomato seedlings. Pertinent parts here:

"Now, have I said anything about fertilizing? NO NO NO. Do NOT fertilize. You
risk burning the delicate rootlets and the seedlings don't need it anyway.
They have the endosperm rich contents of the seed to grow on. Water your
seedlings as they need it, but sparingly, and when the second set of leaves
emerge it's time to transplant. The seedlings will usually be about two
inches high at this point.Experienced folks transplant at even a younger
plant age.And if you feel you MUST fertilize please use a very dilute

    Bookmark   March 12, 2010 at 12:28PM
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Mom's helper,

Thanks for the input. What seed starting/potting mix do you use for your seedlings?

This is the tricky question, because some people claim fertilizing isn't necessary, but one finds out later these people are using Miracle Grow potting soil or some other mix with plant food already in it.

I'm starting mine in straight "organic" jiffy mix with nothing in it, and I'm curious if I need to fertilize or not.

    Bookmark   March 12, 2010 at 12:35PM
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If you use Pro-Mix it says right on the package that you must fertilize after the true leaves appear as it contains no fertilizer, and I think that is true because if you don't the leaves start turning a sickly pale yellow.
However as almost everyone has said, use a very dilute fertilizer so you don't burn your plants.

    Bookmark   March 12, 2010 at 1:39PM
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windclimber(z5 KS,close to KCMO)


I would go with Carolyns advice any way any how.
As you may well know she has more experience with the tomato than any of us here could claim.

In your case I would not fertilize until you pot up and if so, as she suggests VERY sparingly.

I use nothing until germination and when they are strong-- still in the vermiculite, perlite, spag. moss mix---- I will use this solution when the mix becomes completly dry.

1 DROP of Superthrive
2 drops of Mushroom Stuff
2 drops of seaweed extract
In 1/2 gallon of water applied with baster

Basically these are all root stimulants. I do this as they may be in the medium for weeks until pot up when they get into their MG moisture control mix that has lots of the food the plants will need until going into the soil.

I concentrate a lot on the below suface level action.

Root stimulation and tap "damage" (during pot up process) Cold treatment after pot up, above mentioned feeding after germination, correct watering after set out, etc. etc. along with watching out for other knowledge to be gained.

Have fun and hope you have a good season.

    Bookmark   March 12, 2010 at 1:45PM
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I have used Walmart brand (Expert Gardener) and miracle grow potting soil. I like miracle grow better because it is a finer mix. Either one will work fine. I bought miracle grow for this year..$10.48 for a two CU/ft bag. No fertilizer and do not over water as you have found in your above post but plants do like warmth and lots of light. The area where I raise our seedlings is usually 80*. Just keep your soil lightly moist and you should have good results.

    Bookmark   March 12, 2010 at 1:45PM
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After I transplant my seedlings into 3" nursery cell flats and they start growing, I dissolve one tablespoon of Tomato Tone fertilizer in a gallon of water. It does not have much nitrogen in it and part of that is not water soluble so they are not getting hardly any N, but do get the P & K. I use that every other week, the other weeks just plain rain water. I've always had very good plant-s with large rootballs but not long internode lengths.


    Bookmark   March 12, 2010 at 1:48PM
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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

Tony - you are assuming that there is one, and only one way, to properly grow seedlings. That isn't the case. There are lots of ways to successfully grow plants and the methods used will determine whether or not they need feeding.

So you are not going to get a definitive answer to what is your real question - I'm starting mine in straight "organic" jiffy mix with nothing in it, and I'm curious if I need to fertilize or not except to say "That is up to you". But do keep in mind that even plain old Jiffy mix contains some natural nutrients. Not much but some.

You also need to define what you mean by "seedlings" as it means very different things to different people.

To me a seedling is a 3-4" tall plant with 1 or maybe 2 sets of small true leaves (varies by variety) and is no more than 6-8 weeks old. And no, I don't feed them. As the comments you have posted indicate, I believe, as do others that they don't need it and it does them more harm than good. You get root burn and excess top growth that the roots can't support.

For our personal plants, I grow them in Pro-Mix BX which has no added nutrients until they are 5-6" tall and then - weather permitting - they go to the garden and get their first supplemental food in the planting hole.

Those that we grow for sale are bulk seeded in large trays. They get transplanted first at the cotyledon stage into plug trays with plain pro-mix and no feeding. They get transplanted a second time at the 2 sets of true leaf stage (when IMO they are plants not "seedlings") into cell packs or individual 4" pots with more Promix and then we feed with 1/2 strength Earth Juice or a similar liquid fert product once every week to 10 days.

But many continue to call their plants "seedlings" long after they are 2 month old "plants" at 8-10" or more tall and with several sets of leaves. Some even refer to their foot tall plants as "seedlings".

Bottom line - JMO but seedlings don't require feeding but plants do. So try it both ways - feed and no feed - and see which works best for you. ;)


    Bookmark   March 12, 2010 at 2:29PM
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natal(Louisiana 8b)

I germinate and pot up using Sunshine seed starting mix. One year I used a weak fish elmusion solution to fertilize the potted up plants, but haven't bothered since. Once they're in the garden they're side-dressed with Tomato Tone at first flower set. After that it's water and sunshine ... nothing else.

    Bookmark   March 12, 2010 at 2:44PM
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No way you'll get a science paper or research from me but I'll share what I find works great after 20 years of growing tomatoes. First, my seed starter is soiless without any ferts and that's important as to whether or not you should fertilize and when. When I see the first set of real leaves shape, not the seed leaves, then I shoot a little liquid kelp/fish emulsion on them. Every few waterings I will repeat this until they go outside in the garden. My garden is full of compost and I seldom fertilize and if and when I do it's organic.

    Bookmark   March 12, 2010 at 3:00PM
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timmy1(6a ri)


125ppm N
50 ppm P
70 ppm K

Don't feed them like a mature plant and don't starve them either.

    Bookmark   March 12, 2010 at 9:39PM
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I sprout all my seeds in miracle grow soil. I don't have to worry about anything. Easy.

I like easy.

    Bookmark   March 12, 2010 at 9:49PM
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If you examine the ingredients list on a bag of Miracle Gro potting soil, I believe that you will find that it contains "locally" obtained ingredients. That implies that the quality will vary with manufacturing location. I have had bad results using Miracle Gro potting soil bought in the Chicago area.

Last year, I used a home made mixture of 2/3 peat moss and 1/3 perlite (by volume) without lime and it worked fine, but, note that my fertilizer solution contained calcium. I buy peatmoss on sale at Menards for about $5 per 2.2 cubic feet. Perlite is $10.23 per 4 cubic feet at That is cheaper than any premix you can buy.

    Bookmark   March 13, 2010 at 11:31AM
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bencjedi(6 - Central Kentucky)

I start all my tomatoes in 2-cup size deli containers in a sifted peat-vermiculite-worm cast mix. The worm castings improve germination rate. After a week or so when the 2nd set of leave form I transplant them into 4-cell packs. Each plant gets about tsp of straight worm castings. The growth is phenomenal with the worm casts. As a science experiment for school, my wife and I tested germination of bean seeds with and without worm casts. Have a look: From Loris_Bio_Experiment-2010 From 031010

    Bookmark   March 14, 2010 at 11:46PM
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kandm(8b coastal alabama)

I use Miracle Grow mixed at 1/4 strength and give it to them when the first true leaves emerge. I do that about every two weeks. I do this because I use peat moss as a seed starting medium.

    Bookmark   March 15, 2010 at 2:11PM
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Not that I agree, but somebody in this forum named Carolyn claimed that potassium nitrate speeds germination of tomato seeds and thusly recommended soaking the seeds in the "blue stuff."

    Bookmark   March 15, 2010 at 4:32PM
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timmy1(6a ri)

cough, cough...aaaahhhhumm. ;)

    Bookmark   March 15, 2010 at 7:20PM
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Thanks for the input everyone.

Dave I'm glad you clarified definitions. I'm not sure when a seedling graduates to a plant. I'm growing some plants for market as well so it was helpful to hear what you do for your plants.

Timmy, Those numbers might be helpful but I'm not sure how to use them. What's the timespan...per day, per week?

    Bookmark   March 16, 2010 at 8:55PM
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I always just pot them up into miracle gro potting mix. The slow release fertilizer seems to work well on them and they grow fast and well. Once in the garden I don't feed them, unless it's some organic amendment like compost.

    Bookmark   March 16, 2010 at 11:44PM
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helenh(z6 SW MO)

Carolyn was speaking of waking up old seeds. I did not get the idea she recommends the blue stuff for all seeds.

    Bookmark   March 17, 2010 at 9:05PM
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timmy1(6a ri)

Using a 20% N water soluble dry fertilizer. 100ppm N is 6.8oz mixed per 100 gallons water.

Or .68 oz in 10 gallons.

Or .07 oz in 1 gallon.

    Bookmark   March 17, 2010 at 10:18PM
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