Depending on the species and the cultivar, it sounds as though you have little to lose - if it doesn't work, you are only out a year or so, plus, you will then have some idea as to what they are, and can decide whether to do a renovation pruning to the ground or get rid of them, as Ken suggests, replacing them with more suitable cultivars at a suitable distance. I am usually in favor of waiting for a year before doing anything major - other than getting rid of obvious weeds - in a new-to-you garden, since you don't know what the previous owner(s) had planted - sometimes there are hidden gems. I would try limbing up - taking no more than a third of the leaf canopy if at all possible, since more might well spur a heavy growth of suckers - the root system is obviously large... I have a V. opulus 'Sterile' that I WILL limb up this spring/winter - I have been going to get to it for the past 2 years. It seems to be growing from one main trunk, with little suckering, so seems an ideal candidate. Time will tell.

You must have done a wonderful job planting and caring for them last (droughty) summer to only lose a few leaves. The bed I have my last three (of 8) gets fertilizer for the roses but not extra for the viburnum. 10-10-10 is fairly mild as fertilizers go. If you don't see any browning of the leaves or other stresses, I suppose a light application of this fertilizer wouldn't hurt.

There is quite a bit of misinformation that you have been given Mr Jones, I'd definitely take some extra time to sort through it all and make sure that you have accurate facts. I'll go through some, all of which are easily verifiable: Manufacturer and material : All three are very reputable, with Andersen and Marvin having a longer history. That said, Okna has indeed been in business since the early 90's and is a top 100 manufacturer as well. The 3 materials have similar histories as well, as none have been used commonly in a residential window application for more than 20 yrs. All three have their merits, although all three do represent a small "niche" . Vinyl and wood are FAR more common. There is no clear winner here IMO. All are suitable with no decisive pros or cons, particularly considering that each individual product is designed and engineered to exploit the respective materials' inherent strengths, and mitigate its weaknesses. If there is one that I'd put slightly behind the others it would be the Renewal, as adding wood flour/sawdust to vinyl really doesn't add much. Appearance: This depends of course on what areas are examined, however the Marvin all ultrex integrity is by far the slimmest. The Renewal and Starmark are both somewhat bulky by comparison, although neither is very bulky compared to some other products. Despite the slim lines, the all ultrex Integrity is actually the least attractive based on the feedback that I hear. The wood/ultrex on the other hand is bulkier. This category is in the eye of the beholder. Each has its own strengths and weaknesses. Interior appearance: well stated. Some folks would prefer the rich, real wood interior (Integrity) with only a 10 year warranty, others would prefer the synthetic stainable with lifetime warranty and no maintenance (Starmark). Winner again depends on the individual and their needs/wants. Hardware: The Renewal and Starmark both have more attractive hardware options than the Integrity IMO. Both are all metal, both have multiple finishes available. Performance: Here's a big one. To accurately compare, it is necessary to look at apples to apples glass packages. At .25 for a standard double pane package, and .19 for triple pane argon, the Starmark runs away with the win here. With equivalent glass (surface 2 low e, argon fill), the the Renewal and Integrity are .29 or higher. You can switch to any other glass package across the board, and apples to apples the Starmark will be multiple points better. This can be verified via CPD number (certified products directory) at nfrc.org Air Infiltration: Another big one. The reps that you have spoken to are either flat out lying, or being highly manipulative. The only window of the 3 that sees that .05 AI number is the Starmark. The other two are in the teens at best, if not .2+. I would request a structural test data sheet for reference. If renewal or Marvin will provide it, make sure to compare the size of the window and configuration. It is highly likely that your rep(s) are using casement or picture window ratings to compare to the starmark double hung. The starmark is .01 as a casement. Patio doors: Since this was mentioned, the differences as stated for windows continue for patio doors. If the real wood interior is preferred at the expense of performance, then the Marvin or renewal options are better. The Starmark will be a much better performer, but without the real wood interior. Installation and durability: On durability, this is another area that would trend toward Starmark based on containing no organic parts that can rot, and also on the lifetime warranty. Renewal and Integrity are each 10 years (20 on glass). Installation itself will vary by dealer, and should be given proper weight. One cannot speculate on the quality of installation based only on material however. The only thing that could possibly be considered on that line of thinking would be availability to contractors I suppose. Integrity can be purchased by anyone, whereas Renewal and Starmark are exclusive products where dealers are regulated by the manufacturer. One important thing to note, is that comapanies that install Renewal windows are NOT owned by Andersen. They are a dealer that exclusively carries that line and meets Andersen requirements, however they are not actually part of Andersen. Price: This again will vary by dealer and area. Renewal has a reputation as having the highest price, using high pressure sales, and also of posting thinly veiled, inaccurate info where THEY talk poorly about competitors (not to say that is the case here, of course). That said, I'm sure that there are some great Renewal operations across the country, just as there great Starmark and Intergity dealers. Ultimately, these are three windows that are solid to excellent, and each have their own pros and cons. You are unlikely to go wrong with any of the three, it really depends on which options most closely aligns with your goals for the project. It sounds like that is the Renewal at this point, I'd only recommend getting the accurate performance information, and then perhaps that would (or not) impact your decision.

You can prune the bejeezus out of viburnum. If you do it right after they bloom, you should get enough new growth for bloom next year (on all the viburnums I have had, maybe not every variety). Plan your attack, get big loppers and a saw, and go to town.