I am still a newbie, but I think the general answer you're going to get is that it depends on the variety. If you look up a cultivar on HelpMeFind.com for example, it'll give you a general size. I've read, at least in relation to potting, on this forum that you can generally expect the width to be the same as the height, if it's not listed precisely.

Similarly, as with potting, I've also read that unless you plan to keep them close together all the time, you should give them decent space, as the roots will be hard to untangle later, without detriment to the plant. That and blackspot apparently is more prevalent when there isn't enough air flow around them.

If I were to do it, I'd make sure to keep the same variety close together, but I don't think I'd do it elsewise.

ANd of course, I bow to those with more experience, as this is just what I've picked up reading these past few weeks. Feel free to correct me.

~bubbles

Thanks for the response. Actually I've been spacing them close for a while now. However, it appears that I'm getting black spot worse this year than normal. In fact, I'm probably going to try and use chemicals again versus the Cornell Formula that I've been trying this year.