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Tuesday - March 25, 2008

From: Schertz, TX
Region: Southwest
Topic: Compost and Mulch, Vines
Title: Few blooms on native Bignonia capriolata (cross-vine)
Answered by: Barbara Medford

QUESTION:

I have an 8-year-old crossvine that has grown and bloomed beautifully until this year. During the winter it lost all of its lower leaves. What leaves were left had brownish-red splotches on them. It has begun to grow now and has a few blooms at the very top of the trellis. The new leaves look healthy green--no splotches. Two questions: 1. Are the splotches on the old leaves significant? (I can send a picture if you want to see) and 2. How can I get leaf coverage (and ultimately flowers) again on the lower 4/5 of the trellis?

ANSWER:

Two vines that are frequently confused with each other are Bignonia capreolata (crossvine) and Campsis radicans (trumpet creeper). Their blooms and growth habit are very similar, thus the confusion, but the trumpet creeper tends to be much more aggressive, putting out suckers and sometimes damaging structures. We will assume you have crossvine, and the solutions for both are basically the same.

The sudden leaf loss is a little disturbing, but a late frost, or the plant being allowed to get excessively dry might have produced that problem. This is a plant with no significant insect or disease damage, but might sometimes show small spots of sooty mold or mildew. This could be the product of poor circulation. We are inclined to believe it is something in the culture of your plants, rather than pests, that is causing your problems. Basically, flowering bushes need more sun and less nitrogen. If your plant is not getting a lot of sunlight, it can survive, tolerating shade, but it will not bloom as well. And, if you have been fertilizing with a high nitrogen lawn fertilizer, that can certainly cut down on blooms. If you wish to fertilize your crossvine, switch to a high phosphorus formula just before blooming period.

Finally, we suspect that your plant needs a good grooming. Many gardeners cut it down very severely after the bloom period. This will always inspire a plant to try to do better, before it gets taken down altogether. It may be putting so much energy into growing those thick stems that little is left over for blooms and leaves, but every plant needs to bloom in order for the species to survive. Not only that, trimming may also permit more sun to reach the bulk of the plant, as well as improving the air circulation. Crossvines like lots of water (but can survive pretty dry) and nutrients. Compost mixed into the soil will both add nutrients and improve drainage around the roots. So, basically, feed it a little better, maybe water a little more, give the soil a nice dose of nutrients, cut out the nitrogen-high fertilizer, and tidy the plant up once or twice a year. It's a very tough native plant, and your hummingbirds will thank you for what you do.