1 - Prune trumpet vines now while they are still dormant and remove vines growing from the roots in areas where they are not wanted.

Yard and Garden
March 10, 2012

Q. :

Thanks for all the great information you provide. Do I prune this vine now (Feb-Mar)? I would like to encourage flowers and discourage all the runners that come up in my xeriscaped rock areas and nearby small grass lawn. We have about 6 old vines that grow on an adobe wall; they are mostly trained vertically from the root and then cascade all over the wall---pretty in summer, ugly now. Hate to take off the seed pods because the goldfinches love the seeds, but think the seeds falling may be why I have so many shoots/runners (and it is now too late to stop the seed drop, anyway.) Do the flowers grow on old or new wood?

Regarding mustard weeds: Is this the same kind that grows in the Napa Valley in CA? I have it all over the fringes of my corral and also now in some of the rocks. If I cut off the yellow flowers and leave them on the ground, will they still go to seed and sprout (like a dandelion flower, cut off, will still fluff and spread?). Can I rototill them all under and hope that kills them? I prefer not to use 2,4-D based herbicides and I do not think other herbicides work. Your help is appreciated.

A. :

You can prune your trumpet vine now. Since the trumpet vine flowers in the summer, it flowers on new wood. The dormant season is the best time for major pruning. Some gardeners cut their vines to the ground in the fall or spring. Others just prune back vines that are growing in areas where the vine is not wanted.

Seed may be part of the problem with new plants developing in your landscape, but the trumpet vine is also capable of developing new vines from root suckers (stem buds formed on the roots). These may be managed by a non-translocated herbicide (that does not move back through the roots to the "mother plant", or by digging the new vines as they develop. Where you cut the underground roots, you may encourage new buds and vines to form, so remove. You may need to remove the roots completely from flowerbeds and areas where the new vines are not wanted.

You can slow the regrowth of roots into areas where they are not wanted; you can dig a trench, cut the unwanted roots, and install a root barrier. A root barrier may consist of heavy-gauge plastic sheets two to three feet deep and along the perimeter of the area you want to protect. There is also a product called Typar Biobarrier (TM) that consists of a spun bonded sheet of polypropylene with plastic dots across the surface. These dots are impregnated with an herbicide that stops root growth at the barrier. These barriers should be placed vertically between the trumpet vines and the area to be protected, but at the bottom, turn the barrier material outward toward the trumpet vine so that the roots are discouraged from going under the barrier and are directed back toward the vine. Do not leave a gap at the base of the vine and the portion of barrier material turned back. Roots will quickly find the gap and bypass the barrier.

As you prune the trumpet vine roots, do not cut them too close to the main vines. This may cause some dieback, reduced vigor, and reduced flowering, but it could kill the trumpet vines.

And in answer to your question about mustards: In some states mustards (not weeds) are grown for canola oil and other products. The mustards that grow here most commonly are weeds known as London rocket, flixweed, and tansy mustard. They are difficult to manage. Pre-emergent herbicides can help prevent the seeds from germinating, but it is too late to use a pre-emergent herbicide now. If you prefer not to use herbicide, you can dig or hoe them, or rototill them, but do this before they flower. If they are flowering, they may indeed mature seeds if left lying on the surface. If they have begun to flower, rake and remove them from the garden.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

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