I always water my foliage. But never during the hot part of the day. Only in the mornings. It controls many diseases for me.

Most roses can grow beyond their stated size. I have a 14" hybrid tea.
There are small roses. Minis instantly come to mind. Many of mine reach a maximum of 2 feet. Bolero, while not mini, certainly doesn't grow past three feet.

Not sure about pruning. I have to prune in winter just to simulate having a winter lol. It certainly rejuvenates the bush and increases bloom production here.

New Zealand has about 6" floppy stems for me.

How slight? Just a couple leaves and I would just trim them off.

For every one of your questions there will be more than one answer. Every one does it differently. The trick is to find the ones that work for you.

I water my roses when I can, morning, noon or night. I don't have a drip system so I use soaker hoses, sprinklers and the hose. I often spray off the leaves to keep them clean. Whether that helps with diseases, who knows, but I don't think it hurts.

Sizes will vary greatly by zone and even by individual garden. Warmer zones have much longer growing seasons so roses can get larger. But even in my cold zone many roses have exceeded their "stated" sizes. Of course, many others never got any where near as large as advertised. So you really never know.

Pruning does encourage new growth. Whether it gives them longer stems or not I think depends on the variety of rose. Exhibitors hope it will give them those nice long straight stems they need for rose shows. On some varieties it may work but some roses just don't have that type of growth habit in their genes.

I got New Zealand last season and as a new rose it did have short stems. I may not get to see if that changes with maturity since I don't think it made it through my severe winter.

It isn't a bad idea to let the supplier know that the rose was diseased when you received it. They may not do anything about it but they should be made aware of the situation. There's always a possibility that it came down with it during the stress of shipping and usually will clear up quickly once it's in the sun again. I know I often see roses lined up in the nurseries with black spot all over them. Sometimes the conditions of crowding, high humidity and little air circulation will cause such outbreaks. I don't let it deter me from purchasing because I can isolate it at home until it clears up.

So don't be afraid to do a little experimenting and find the answers that work in your garden with your roses. Most of all don't get too caught up in all of the "stuff" surrounding rose growing and spend a lot of time just enjoying your roses!

I learned this year that watering the leaves prevents mildew. Counterintuitive, but there it is.
I also water "whenever", since I am not a morning person ... on the other hand, when I do get up, I will spray/mist leaves, buds and flowers on my roses if the temp. is going to go over 80 (which, around here, it often does). This can make the difference between having a beautiful rose at the end of the day and contemplating a shriveled mess.
Soaker hoses are a great way to water roses. Mulching is a must. A ring of stones around the root perimeter can also help your roses from drying out (as well as helping to keep your mulch in place when the wind blows).
Pruning is really not that difficult. During pruning season, I walked around the neighborhood to see how everybody else's roses looked when they were pruned. Then I went home and essentially copied what they'd done. There are also free pruning workshops all over the country, often offered by local nurseries. Don't fear the pruner!
Good luck with your roses.

I agree that the location/region plays a role in all these rules.

Whenever I water my roses, I always water with a water hose or manual sprinkler that gets all the leaves plenty wet. I water in the morning or evening. The day temps get up to 90-100F (or higher as the summer comes) and the night temps get to 80-90F, so while I have always been cautious about watering at morning or night, I also have not experienced the problems that come with damp soil overnight or wet leaves on plants. So for my decorative and vegetable plants, I continue watering the way I do, since it, so far, doesn't have any negative effects.

I have let the roses grow on without pruning, and I have also pruned. When I did not prune, it did not seem to send out more branches to make a fuller look. Instead, I just got tall, lanky stems all season long. It seemed as if it did not need to grow as many more stems, so it didn't. It was happy with what was already there, so it would just make flowers. However, because there wasn't so much new growth, the flower bloom also was not as copious.

I think the better result comes from pruning. When I pruned, new stems and branches would grow, and new buds would form, and ultimately lead to more flowers.

This first statement of Seil says it all...

(Seil wrote)"For every one of your questions there will be more than one answer. Every one does it differently. The trick is to find the ones that work for you."

I hose the foliage nearly every time I hand water (once every week or so, depending on weather). The bushes are adjacent to a street, so there is plenty of heat, dust, exhaust flying around. I think they like it (the spraying, not the street!).

It's 100 degrees out there, but I went out anyway to see if the stems on New Zealand were short, and I saw some 6", some 8" or longer. But I've never noticed any tendency to have a lot of 6" stems. I'll also comment that a tree branch has caused it to have some shade, and I'm pleased with it's ability to tolerate that shade.

Commenting on mildew? No, I wouldn't bother. It's so common. (I did tell the nursery people that a tomato had a big juicy hornworm on it though!).

When I started with roses a year ago, I went on Youtube to learn how to prune them. After watching some footages where people with over a hundred roses to take care of and they just whack the bushes down by as much as half, hubby told me that some people like to push their roses to bloom at maximum speed and number by severely pruning the bushes, which also results in shorter life spans for the plants. That method seemed brutal to me anyways, and since I don't care much about the sizes of the bushes, they don't need to look even or uniform, I decide not to prune my mature plants or my 1 y/o plants, waiting to see what would happen. Now that all the plants are blooming again, I can see that if I want to have more cuttable blooms for bouquets (long straight stems), I should prune the plants--I guess the key is just how much, guess next winter I will give it a try. (I learnt that at least the horizontal laying cames should go)

If watering the foliage isn't harmful to roses, why did Heirloom's planting instruction say avoid getting the leaves wet? That's how I got the habit of trying not to wet the leaves.

About the sizes of rose plants, how did they come up with the numbers since if allowed, all roses can keep on growing taller and taller year after year? (not including mini's which I'm not familiar with) I'm sinply curious.

Socks12345, my New Zealand is actually in heavy shade on both ends of the day, it only receives full sun for about 6 hours at this time of year, I chose this spot b/c I heard it prefers a cooler environment. So far it only has a few blooms on short stems (6"-10"), perhaps it will have more blooms when it grows more? Guys how floriferous are your New Zealands??

The thing you have to remember is that a lot of the things we've traditionally been taught for decades about growing roses are changing as new technology and research has developed. Like a lot of aspects of our lives times change with new knowledge. So much scientific research has been done now on exactly how the plants grow and react to pathogens that many of the old ways are now being updated. But some people are quicker to accept new things than others so the old methods persist in being put out there. It doesn't mean that one way is all wrong or another is all right. It just means there is more than one way to do any of it. Like I said before, experiment and do what works best for you and your roses.

Water on the foliage will cause blackspot to germinate if it stays wet for around 8 hours. So don't wet the foliage in the evenings.

Hosing down the foliage does help control mildew, but mildew is not usually a problem in the East except for maritime New England. I don't do it because it wastes water.