Fertilizing seedlings

As seedlings begin to grow this season, I am wondering about fertilizing them:

  • what kind of fertilizer is best?

  • when should seedlings be fertilized?

  • how often should fertilizer be applied?

I am growing the seedlings in an equal mix of peat moss, vermiculite, and perlite.

Thank you!

That is a great question that needs multiple factors taken into account. Are you growing your seedlings under indoor lights? What temps?.. Things like Miracle Gro and Rapid Grow have nitrogen primarily as ammoniacal N. This can build up in plants and become toxic. Outside the warm weather and microbes break it down to nitrate which can be stored more readily in plant tissue without becoming toxic. If you have low light and relatively cool temperatures then I suggest using a dark weather feed with N primarily in a nitrate form so toxicity would be less of an issue. I wrote an article in the American Rose magazine that was printed last August on this. I show a picture of a seedling with ammonium damage (necrotic leaf margins) in that article.

This is what I recommend-

-Get a high nitrate balanced fertilizer (typically sold in the North for greenhouse crops) for your seedlings if grown inside under lights or a cool greenhouse.

-Don’t overfertilize. Perhaps 150-200ppm Nitrogen once a week is good after the first few true leaves have come out. Later it can be bumped up. Fertilizer is only helpful after the seedling has some leaves to conduct photosynthesis and then use it.

-When you water “flush the John” by watering until it comes out the bottom, otherwise fertilizer salts will build up in your pot and damage roots.

Hope this helps.



How about Osmocote for seedlings growing in basement (65 deg F) under fluorescent light?

My seedlings seem to like Osmocote, but there have been (?) some negative comments about it.


Dave W

Thanks for the super information, David. As you rightly guessed, here in the PNW, the temperatures are remaining relatively cool (though we are supposed to get into the 60s in the next couple of days). These seedlings are primarily being grown outside with plenty of light, but it sounds like special care should still be taken.

Again, thanks for the great data.

I do not fertilize until the seedlings are abaut two weeks old.

At first 1/4 strength water soluble for the next two weeks. Then I go half strength for 2 weeks.

After that full strength, but if it says 1 teaspoon per gallon, only a level teaspoon and not heaped !!! A little less is better than too much !


George’s recommendation is right on the money. Over-feeding will lead to mildew-prone growth, so go easy.


I have been thinking about this subject too, as I have lost some seedlings due to wrong fertilizing. Most of my seedlings are now in peat pots, so it is difficult to water them until the water comes out of the bottom. To avoid further dead among the seedlings, I now only use fertilizer in very small solutions and not very often. The seedlings though are not impressive in size, which could be due to too less use of fertilizer. Any suggestions will be appreciated.


I forgot to mention in my post above :

After 2 to 3 times watering with fertilizer I do one watering without any fertilizer.

When I did my first own root mini cuttings in the early nineties I always had problems with the roots going brown after transplanting into larger pots. My friend, the owner of the local Mini Nursery suspected that I “OVER FERTILIZE”. He was right ! He gave me his electronic instrument, or salt meter, and it went off the scale.

I was always careful with fertilizing new seedlings, but NOT with transplanted own root cuttings. I learned another lesson and from then on I was fertilizing the rooted cuttings just as carful as new seedlings.

Very valuable help from all on this question. I have done some looking for high nitrate (not ammoniacal) nitrogen fertilizer, but with little success. What about “nitrogen derived from urea?” How would cottonseed meal work for starters?

I just had an e-mail from another Canadian hybridizer, asking me what water soluble fertilizer I use ?

I get it from my friend Brad Jalbert the owner of Select Roses and I asked him what brand it is. He switched to it a few years ago and it is the “BEST ever” he told me. Btw, Select Roses is growing the “Best Minis” in N. America. I know, because I delivered hundreds of his minis to RS’s in the Seattle/Tacoma area years ago before 9/11. It’s too much hassle now to take anything across the border.

He is buying it from SUNGRO HORTICULTURE. Link to web site below. I get my Sunshine Mix #4 from them too. Check it out too.


It is Technigro 17-5-24 Plus and you find it under products etc.

Technigro 17-5-24 Plus requires 13% less fertilizer than comparable 15-5-25 fertilizers for effective feeding. Higher magnesium and sulfur eliminates the need to supplement feeding with epsom salts, and higher molybdenum eliminates the need to supplement with ammonium molybdate or sodium molybdate. Moderately low potential acidity. Good for feeding when cool, dark growing conditions are prevalent.

Available in 25 lb. bags.

Applications : Great for all crops.

Link: www.sungro.com/