At what point do you start fertilizing seedlings?

And at what rate?


I’m using something called Cal-Pot (calcium potassium)Special which is made by Plantex. I am using it because it is high in the nitrate form of nitrogen and am using it at 100ppm Nitrogen. I grow my seedlings in the cool basement and fertilizers like Miracle Grow and most other standard water soluble ones have resulted in ammonium toxicity. Their nitrogen is mainly in the form of ammonium and urea. Under outdoor conditions where it is relatively warm microbes convert urea to ammonium and ammonium to nitrate making both ammonium and nitrate available for plant growth. Under cool conditions this transition doesn’t occur so readily. Since ammonium cannot be stored in plant tissue as well as nitrate can before becoming toxic, seeing burned leaf margins on older leaves due to ammonium toxicity is common.

There are other fertilizers too which are high in nitrate such as Peters Dark Weather Feed and one of the Peters 20-10-20 formulations (there’s one that is not as well).



Hi Shane:

I start fertilizing the seedlings with a soluble fertilizer within about 4 weeks of germination. Actually, I add granular fertilizer to the planting mix before the seeds are planted. I start with a very dilute mix of soluble fertilizer - probably about 20% strength or less.

Jim Sproul

David and Jim,

Thanks as always! After a disasterous year last year I am doing everything possible to prevent damping off, including withholding fertilizer until absolutely necessary. David, that is very interesting about the form of nitrogen. I have noticed that many of my seedlings indoors have done worse since I starting applying 1/4 strength Miracle Grow at every watering. It could very well be toxicity.

Shane, are you growing indoors? If so…I have found that putting an oscillating fan on a timer to come on several times a day, does a nice job of keeping “damp off” at bay. Now, for the life of me I can’t remember where I had originally read about trying this…it was several years ago when I was growing annuals and perennials indoors (before I tried growing roses from seed)…but I can attest to the fact that it actually works.

I use an air cleaner which does similar. I just aim the jet of air it expulses at the wall and the air stream disperses around the area.

Makes sense. I hardly ever have dampoff losses here in the dry climate of the southwest.