Agree with gardengal48. It's to get the bulb roots started before the first frost in places where the frost will arrive ahead of any significant end of summer rains. Once the roots have started the bulb closes down for the winter and goes into 'anti-freeze' mode. Usually the roots start months before the green shows above the soil. For those of us with autumn rains and temperate weather - it's not something we need to do, but it is very important for gardeners who work with the inner continental extremes.

You not only can, but should fert your container plants in the heat of summer. Plants are like children. When they go through a growth spurt, their nutrition needs increase. When they are in a lull, their needs decrease. There are cool season plants that generally die or go (semi)dormant in the summer and any plant that is going dormant shouldn't be ferted, but any plant actively growing needs to have it's nutritional needs met. I suspect that most, if not all of your container plants are warm weather plants that do best in warm temps. If so these will require food during their 'growth spurt' for optimal performance.

I'll chime in here, having lost at least $1000.00 worth of fruiting trees, vines, and shrubs several winters ago. If your trees are in basins you have two options; you can either bring them inside into a garage or shed (provided it's insulated) before the ground freezes or you can dig holes and put them pot-and-all in the ground. NO MULCH! I was not able to plant all of my trees before the ground froze and I lost a lot of trees to simply frozen roots, but the most damage happened because of mice. I don't think it was voles; I've never seen a vole in Colorado. I had dug a long ditch in which I planned to plant my grapes. I thought I could just drop my pots in the ditch and fill it up with leaves to protect the roots from freezing. When spring came I took a look and I thought I could die. All of my trees were sharpened on the trunk as if they were going to be used for arrows. Little tiny teeth marks were all along the base. I still have not replaced everything I lost. For what it's worth, the few things that did survive the mice did make it through the winter also. The winter before this happened I put them in the garage. They did fine there but I had to keep them watered some. The biggest problem was that they broke bud way too soon and the aphid problem was unbelievable. This was not the easiest way to go but I did not actually loose anything with this method. If there is a reason you can't plant them then you can do either of these methods. If you can plant them, even in their pots, then I would suggest this. You avoid the need for watering, for the most part, and the insects will stay at bay. If you need information regarding when to expect the first frost the link is below. I would be more concerned about winter protection than when to stop watering. Here is a link that might be useful: Colorado Climate Charts

A cool season grass won't necessarily go dormant in CO. If you fertilize it with 1 lb of N per 1000 sq ft after the top growth has stopped, but while it is still green, it could well stay green all winter. However, you probably don't need to water it for much longer. I think the people with unmetered irrigation water here have the water shut off on October 1. You probably want to aerate whilt it is still growing.