Which viburnum plicatum do you have? I have two: Shasta and Summer Snowflake. They are woodland plants, so yours would benefit from some peat moss. Mix it with good gardening soil, and put it on top like you would put mulch on. You can do it again later in the summer and in the fall. You can then mulch on top of it too. These viburnums don't really need to be fed- it all goes into the leaves, and not flowers then anyway. But,...they don't like the wind. Is your place windy? The odd branch- no idea. Why don't you prune it?

Good shrub. Viburnum 'Carlesii' is fragrant. I think the cultivar 'Winterthur' is awesome.Don't know much personally, or I'd tell you species, but here's some info I saved that explains these a bit easier. All old stuff to some folks as many Viburnum discussions have taken place. Please bear with, yet enjoy the information! An accompilation of notes I saved: "(For fragrance) You can start quite early with V. farreri 'Candidissimum' or 'Nana', which are just about ready to bloom right now. The V. x burkwoodii and V. carlesii cultivars can string out the fragrance season for up to a month. I have my house encircled with every possible cultivar. If you are looking to feed the wildlife, enter the world of V. dentatum and the myriad of cultivars that bloom over a long period. We can steer you to cultivars that bloom close enough in sequence to maximize fruit production. The V. plicatum tomentosum group also fruits heavily in some cases, as does the V. dilatatum and related, as well as V. sieboldii. You can run up to Ridge Road Nursery, the home of V. sieboldii 'Wavecrest', and get one of the finest types(be sure to add another related type to maximize fruit production). V. lentago, V. prunifolium, V. cassinoides, V. nudum, and V. rufidulum are the natives that also produce abundant fruit. V. rhytidophllum, V. lantana, and the crosses all make lots of fruit. We need more info on what you are looking for to steer you in the right direction. Alternatively, you can take my and VV's approach and just own them all! For fragrance near the home, follow my lead! Around my house are 'Mohawk', 'Chenaultii', 'Summer Hill', 'Aurora', Judd, 'Cayuga', carlesii compactum, 'Spiced Bouquet', 'Fullbrook', 'Sarcoxie', V. carlcephalum, 'Diana', and now several Classic Viburnum cultivars to add. Fruit production is actually quite good on these plants with all the cross pollination going on. I have changed my tune in that regard---you CAN have fruit and fragrance. Large shrub/small tree types--V. prunifolium, V. lentago, V. rufidulum--plant these three together for cross pollination and large amounts of fruit. 'Summer Magic' is an excellent V. prunifolium cultivar--ask me again in a few years and I will have comments on more cultivars that show promise now. Along the same lines, V. sieboldii 'Wavecrest', 'Seneca', and 'Ironclad' can be planted together for a good show. Smaller shrubs(can take wet)--V. cassinoides and V. nudum have massive fruit set with terrific berry colors. 'Winterthur' is one cultivar, but I have not seen it to be any better than the typical seedling. Great fall color with both. Smaller V. dentatum for flowers and fruit--Papoose, Blue Blaze, Raspberry Tart, Little Joe(no fall color) Large V. dentatum--the Klehm hybrids all bloom together and have wonderful fall color and fruit production--Cardinal, Red Regal, Crimson Tide, Indian Summer V. dilatatum--all flower together, all produce ample fruit(so much so that they are looking to be invasive in the east). V. plicatum tomentosum--a special shrub, perhaps the most beautiful in flower, and some are great fruit producers. Try Shoshoni or Newport for a shorter version, Shasta and Mariesii for larger types. Magic Puff is also one that is supposed to be smaller. Molly Schroeder is newer and has pink flowers that rebloom. I have tried to accumulate all these cultivars that I can find as I think they are just a fantastic plant. V. lantana and related--there is a variegated V. lantana, as well as a yellow leaf version, both mildly interesting. I like the leatherleaf V. rhytidophyllum and V x rhytidophylloides where space is not an issue. They are whoppers, 15X15 is not odd, with massive flowering and fruiting to boot. Some say semi-evergreen, which for Zone 5 means crappy tattered leaves that last into January. Birds absolutely love these plants. Good nesting sites. Viburnum dentatum var. deamii, one of the most glossy leaved plants around though similar in other respects to the rest of the arrowwoods. I'd throw a pitch in for Viburnum molle, too. That's the Kentucky viburnum with exfoliating bark but similar to arrowwood otherwise. Viburnum nudum "Wintherthur" and "Earthshades"!!!! Fall Fruit is outstanding!" (Dax Sept. 2006)

I am in zone 4 Montana and constantly push limits with zone 5 plants. I have had only a few others which also survived but didn't flower. I tried Oakleaf Hydrangea and had the same results - survived but didn't flower. I grow Viburnum carlesii which is usually listed as zone 5. It blooms beautifully. I have had it for 8 years. If I had room for a Double File I would try it in a heartbeat because I have great success with Zone 5 plants. I think nurseries are conservative in their estimates regarding zones. If I see zone 5, I order. We can have some awful winters here - definitely Zone 4. I now indicate I am from zone 4b (warm zone 4) because I have had such good luck from nominally zone 5 plants. I would very definitely think you have a good chance Doublefile viburnum would survive in southwest Wisconsin which I would expect is significantly warmer than where I live. Some of the "zone 5" plants I grow are Buddleiea, Clethra, Fothergilla and Hamamalis (Witch Hazel). I hope you do try it. I'd love to find out if it works for you if you end up trying it out.

There are 4 possible explanations that I can think of; sun, soil, water, and genetics. Soil includes nutrients, ph, drainage as well as composition (organic matter, for example), which can all really vary within 6'. You probably know if one of these gets more sun or moisture, and how the soil was prepared when you planted them. You probably also know if one is larger or has grown more rapidly than the other. You could have a detailed soil analysis done on samples from the rootball area of each, and I guess that's what I'd do. That, and start some cuttings of the one that flowers, in case you need a replacement for the 'bad twin' - if you can rule out all the possible variables you'll be down to genetics. I would not assume that that;s the problem until I looked at all the other possibilities, though.