Hello and thanks for your question. I have included a link to an Oregon State Extension publication that is called "Growing Blueberries in Your Home Garden". This pamphlet talks about how to fertilize both established plants and new plants. Depending on the maturity of your plants there are different requirements for nutrition. None of the fertilizing requirements call for a fall application regardless of the age of the plants. In general it is not good to fertilize plants in the late fall as it could cause a growth spurt when the plant should be shutting down getting ready for the winter. New growth caused by the Nitrogen provided and will be damaged by a hard freeze. This publication recommends adding fertilize to a blueberry plantings three times between April and as late as July depending on the maturity of the plants. http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/12202/ec1304.pdf;jsessionid=A8C6BEA4AE18F6369D7C133B43A88292?sequence=1 It also discusses the mulching of blueberries. In general sawdust decomposes at a rate of about an inch per year. Established plantings of blueberries can have a layer of mulch of about six inches. You can replenish the mulch at any time of the year.