Garden Q&A: Morning glories running wild

Question: I read the article about morning glories you wrote this fall, and I have a problem with wild morning glories.

Years ago, I planted blue rug junipers on a bank in my backyard to keep the weeds from growing. They were doing really well until two years ago.

It seemed that overnight I had a lot of wild morning glories growing in the junipers.

I tried pulling them out, but they keep coming back with a vengeance.

Is there something that I could put on these to kill them without harming my blue rugs? I'm afraid that if I don't do something, they will eventually kill the blue rugs by choking them out.

Answer: Field bindweed ( Convolvulus arvensis), also known as wild morning glory, is a challenging weed to eradicate.

According to recent studies at UC Davis, the best control method involves repeatedly “top killing” the plants — physically removing new growth by pulling it out.

The trick is to remove the growth as soon as you see it, eventually starving the roots of a carbohydrate source and killing them.

The process does take time, but it is the most effective way to rid your garden of bindweed.

The same study notes that repeated applications of organic herbicides provide a means of “top killing” and are quite effective when used consistently.

The trouble is that if these products get on your junipers, you'll kill them as well. Because of that, I would avoid using sprays and stick with hand removal.

I'm aware of what a difficult job this will be.

To cut down on the number of vines that emerge from the soil, you need to put a protective mulch covering over any exposed soil. If there's space between any of your junipers, lay down a layer of newspaper 10 to 20 sheets thick over the exposed soil and cover the paper with a layer of 2 to 3 inches of shredded hardwood mulch. This establishes a physical barrier to weed emergence.

You'll still have bindweed popping up in the junipers, and those vines will have to be hand pulled, but the newspaper mulch will drastically cut down on the number of shoots developing. You'll have to re-mulch the area each spring.

If there's no space between the junipers, your only option is to hand pull the bindweed.

I wish there was an easy answer, but unfortunately, there are no alternatives that don't involve potentially harming the junipers or digging them out and replacing them.

And, whatever you do, don't ever till the area. The roots of bindweed can be up to 10 feet deep and tilling will just chop them into smaller pieces — and each will grow into a new plant.

Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio. Send your gardening or landscaping questions to tribliving@tribweb.com or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.