Fertilizing dormant container plants over winter?
Over the last year I've repotted many of my plants into Al's 5:1:1 and Gritty mixes, and I've noticed a world of difference in my plants' vigor and overall health. Much wonderful knowledge and advice is disseminated here, and I'd like to thank those responsible.
I have been reading Whitcomb's Plant Production in Containers; in one section he stresses the importance of fertilizing container plants over the winter, and urges the reader not to neglect this routine task. Of course, this is an old text and best practices may well have changed over the years for all I know. I have never fertilized over the winter before, but I understand the general importance of fertilization during the growing season with these well-draining mixes, and I'd like to ask for your thoughts here.
Some specifics: I am concerned mainly with conifers (pine spruce etc.) and japanese maples, which are being overwintered in my unheated garage. Temperature in the garage is typically 5-10 degrees higher than outside, but never gets below 25-30 *F. I use the skewer method and water as needed, approx. every 2-3 weeks over the winter. Looks like another weird winter is underway, and they're calling for the temperature to climb to 55-60 *F for a stretch of 3-5 days later this week, though we usually see 20-35 around this time of year.
What are your thoughts on the need for fertilization over the winter? Yes, no, how much, when and perhaps most importantly, why?