If the ground is still frozen and the roses haven't started to grow yet it's too early. They won't be able to take it up. The soil needs to be warm enough for active growth in order for the roots to absorb nutrients. I would wait until you can see the bud eyes beginning to get plump before applying any fertilizers. If they are fattening up then the roots are awake and will be able to take up food and water.

I usually wait to prune until the forsythia begin to bloom. Yes, it's an old wives tale but a good one because it means the soil has warmed up enough for growth to start. That's when I begin to prune and as soon as I've finished pruning I put down my first application of a slow release fertilizer.

Thanks Seil.
That's what I was going to do.
Wouldn't it be better to use a fast release fertilizer to get the growth started and use slow release a month later?

You have to be careful pushing plants in the spring. While the horrific spring freezes aren't really part of our experience, a big part of that is because spring moves slowly in this part of the world. So when the thermometer plummets in late April, instead of screaming about death and destruction, there isn't much out there yet to die.

The best way I've heard to try and game the system is to apply slow release *organic* fertilizer early. When the soil and plants wake up, it will start working. By an amazing coincidence, this is the same time that the plants will be able to make use of the fertilizer. Then, when they are actively growing in May, the regular fast acting fertilizing can start.

The biggest factor I've found in how well they are going to grow is heat. Without that, there isn't a lot you can do. That is the real gating factor. Not food, not water, but heat.

The only time I would use a fast nitrogen is if I was having a big party in my yard or a wedding or something. Then I would use Miracle Grow for roses. BUT it's been my experience that it comes with a price. One gets alot of top growth and the roses get so leggy they fall over. I only use that if I'm so impatient I can't stand it. Otherwise..good organic soil and fish fertilizer is my favorite.