Digging In - Advice on Doublefile Viburnums: A Case of Mistaken Identity?

By Scott Aker
Special to The Washington Post
Thursday, February 5, 2009

Q I have two doublefile viburnums planted next to each other. For the past three years, one has failed to bloom while the other blooms faithfully every spring in spite of drought and neglect. How do I coax its companion into flowering?

A You may believe the two are identical varieties, but they might be different even if they were labeled the same at the nursery. The botanical name for the doublefile viburnum is Viburnum plicatum tomentosum. Unlike its parent species, the botanical variety tomentosum has a ring of showy sterile flowers surrounding a cluster of far smaller fertile flowers that are capable of developing into fruit. Tomentosum blooms two to three weeks earlier than the straight species. And when it blooms, V. plicatum has only sterile flowers. Even if you do have tomentosum, there are several different cultivated varieties of it. These differ in habit and also at what age they begin to bloom. It's conceivable that your non-bloomer simply hasn't reached flowering maturity yet.

If the plants are genetically identical, equally healthy and the same age, I'm at a loss as to why one would bloom but not the other. Like many shrubs, overly vigorous growth in viburnums may suppress flowering. Do some root pruning in the spring to see if you can check its growth and stimulate flowering.

Use a sharp shovel to cut some of the roots just inside the drip line, creating a sort of dotted line around the circumference of the shrub. This may spur blooming the following spring.

I read about using repellents on tomatoes, namely hot pepper wax and blood meal, to keep rodents from eating them as they turn red. Will these products affect the taste of the tomatoes? Also, my tomato plants were afflicted with fungal disease last year, and I wonder if it will carry over in the soil for this year's crop.

In spite of its name, hot pepper wax doesn't have an odor or flavor. Blood meal does have an odor, but it won't permeate the fruit, and if some is lying on the fruit at harvest time, it can be easily washed off.

Tomato diseases are notorious for lingering year to year in the soil. In commercial production, growers allow fields to lie fallow or plant unrelated crops for four or five years before planting tomatoes in the same ground. In areas where land is at a premium, soil is sometimes fumigated or solarized so tomatoes may be grown year after year.

If possible, move tomatoes every year. You can even incorporate them in a perennial garden or flower beds for a few years. Large containers are another option. Don't grow other crops in the nightshade family in your tomato beds. Peppers, eggplant, ground cherries, tomatillos and potatoes are subject to many of the same diseases as tomatoes and will allow them to persist.

In recent years, heavy spring rains have played a major role in all the disease problems we have seen. In many years, it is better to wait to plant tomatoes until early June when drier, hotter weather arrives and diseases are less likely to be severe. Fruits that grow in the warm, dry sunny days and cool nights of autumn develop far more flavor than the midsummer crop.

Scott Aker is a horticulturist at the U.S. National Arboretum.

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