I've just spent several hours on ICL's web page, and am more confused than ever.

My situation: I grow a variety of landscaping and native plants in Central Alberta. We are Can Zone 3, roughly USDA zone 2. We average about 140 frost free days a year, but summer temperatures are cool, with 75 F being a warm day, and most nights getting into the high 40's, low 50's. Most of my plants are here for 3-4 years, and by the time they leave, the soil is exhausted. This is reflected in the low growth rate the last two years.

Pots are mulched with 2" of flax straw for weed control

I'm looking for a product that can be applied on top of the mulch.

The shortest controlled release fertilizers I've found are 3-4 month, and that's in average 70 F (18 C) temps, substantially warmer than we are. (Ave = (H+L)/2)

I don't really want to have fertilizer that will keep plants growing into September. Most of my plants have a spurt of growth in spring, then are finished by mid July and sort of drift from there, getting ready for next year.

Option:

Use controlled release fertilizers, but use less, and hope that the growth stops in time for prep for fall.

Use conventional fertilizer, but a a much reduced rate since it will be fairly rapidly released, and do 2-3 applications per season. 100 lbs/acre = about 1 gram per square foot. So using something like 20-10-10 would be about a gram per #1 pot to about 7 g /#10 pot.

If you have a container nursery, what is your approach to fertilizing?