My preference is to use controlled release fertilizer with any potting mix and also use soluble fertilizer once the plant starts growing vigorously. I used to use Promix and if I remember correctly the directions say to begin fertilizing right away. It stands to reason that no store bought potting mix would have a significant amount of fertilizer in it because the fertilizer would be activated by moisture. Some of these bags sit in a warehouse, or outside, for months or years. One of the big myths of the consumer gardening industry is that a bag of potting mix has everything you need to grow a healthy plant for months. What they have is enough for the first few weeks.

Ohiofem brings up a good point. Most of the pre-mixed soils you buy have SOME level of fertilizer in the mix, but who knows exactly how long that fertilizer charge will last? Also fertilizer levels probably depend on what kind of plants you are growing.

I always add 1 Tbsp of Osmocote Plus per gallon to my soil mixes, then fertilize with half-strength does of water-soluble MG. This seems to work very well for trees in containers, but for flowers or veggies with fast growth rates you might need to change that a bit.

Hope that helps.

TYG

That's what I thought. I intended on adding a CRF that has magnesium and calcium in addition to watering with a diluted solution. For the most part I did that last year except that I added hemlock mulch to the promix along with all the other ingredients for the 5-1-1. Now I realize, you should use one or the other and for me, the promix will be less taxing physically. So thanks, that helps.

Ohiofem brings up good point. But companies like MG sell potting mix that is claimed not to need fertilizing for 3 months. That indicates that the mix already has CRF?SRF. but then the fertilizer sitting in that moist medium for months should be mostly released . So that is another minus for using them beside being so soggy.

I also agree with Robin... ;-)

I would add a small amount just to be on the safe side.. ( CFR). Then add water soluble fertilizer fertilizer diluted at first.. Then once I see the plant healthy, I would fertigate as usual...

Good luck!!!

Laura

Thanks, Laura!