You would count the hours from when the sun reaches the rose, to when it no longer reaches the rose.
For instance, if the rising sun throws a shadow over the plant, which moves after one hour, you would count from 8 a.m.

Also note that the angle of the sun varies from one time of the year to another, and that may alter the hours of sun an area receives.

Jeri

The hours of sunlight vary with the position of the sun in the sky. On the equinoxes, the first day of spring and the first day of fall, every place on earth gets 12 hours of sun, and 12 hours of dark.
Then going into summer, (Northern Hemisphere) the days get more hours of daylight, but with more northern areas getting more daylight faster (which is why northern Norway is called the land of the midnight sun= 24 hours of sunlight per day.

Get your library to get Rodale's Passive Solar Energy book. There are several chapters in there on figuring out how many hours of sunlight you will get. It also shows how to sketch houses, fences, trees onto the thing you use for counting hours. You really need to get this book, because you'll find that the garden spot you mention above when sun begins at 3pm may get a lot more hours of sunlight June and that can make a difference in the number of hours of sunlight.

I saw a gizmo in a garden catalog that you could stick in the ground and it would tell you how much sun that spot received. Of course it would change based on the time of year.

I have come accross some explanations about the type of shade also: Building shade vs. tree shade. I can understand the deep shade vs. dappled shade. But it was said that building shade is better than tree shade. I don't know if this has any significance for roses. Do they care about the type of shade?
The problem is: I do not have 6-8 hours of sun at those locations. May be 4-5 hours at the east- northeast side of the house (not next to the house). So they get shade of the building after lunchtime. But may be during the summer the sun will travel higher in the sky and they will get longer sun. I wanted to ask before digging, planting and waiting.
Thanks for all the input.

Building shade--if the building happens to be white or a light color, the plant can get some reflected light as light bounces off the white building.

The thing about tree shade is that trees also bring root competition, which roses are ill-equiped to handle.

The length of your growing season is also a factor. Think of Florida, where roses can grow 365 days a year, vs. PA where the growing season is much shorter--every hour of sun is more important in PA than in FL, where not only do the roses grow year round, they also don't lose canes in the winter due to freezes.

Senko:

Why don't you try putting the rose in a pot and putting it in the spot and see how it does before planting it. Some roses will do well with less sun than others.

I guess. After all, it varies according to the time of year.

One good way it to plan to hold an afternoon party in the shade, then find out that it is too blindingly hot until 4 PM. That worked for me.

Rosefolly

Geee! I thought you were going to talk about yourself, and how much Vitamin D you needed if you were so many hours in the sun. Was I ever way off.

However your subject is interesting. I have some roses on the west side of the house that get sun from about noon until sunset. I have always thought that they were fine, but now I wonder if they have enough sun.

Sammy

Carol: That is what a logical person would do, of course. But I am not in a logical position anymore: We were out of the country for 4 years, so no gardenning. Then came back, buying the house and etc. so no gardenning that year. The following summer we put all the landscaping, that was last year. They were working in the good part of planting and growing season, so no gardenning, well minimal gardenning with some annuals and couple of perennials. Now, this year I am gardenning! They are going in and growing (hopefully) ASAP. Can you feel my pain? So, you know, I have no patience left to wait and study them anymore. But thank you for you suggestion.
Sammy: If it is working don't fix it. If you never thought about it, it is working.

Senko - Where are you located in PA? I am outside of Philly, in Montgomery County. There are a handful of us from the SEPA area and can offer up all kind of advice! Good luck!

Hi Carol,
I am not too far, at Bucks County, north of Philly. Used to live in Montgomery County some years ago. I do not know who else is around this area. Perhaps not many on the GardenWeb.