Friday, January 30, 2015

Wet winter, spring affect bearded irises

Acacia (Wattle) can be seen in all its golden glory in the UC Davis Arboretum. Stuart Pettygrove/Courtesy photo

May 5, 2011 |

Learn more

What: Free garden workshops offered by Yolo County Master Gardeners

When: Saturday, June 4; 9:30 a.m., “Attracting Beneficial Insects to the Garden”; 11 a.m., “Lavender Distillation”

Where: Central Park Gardens, Third and B streets, downtown Davis

By Diana Morris, Merle Clarke, Gail Oliver and Willa Pettygrove

Q: I have a couple bearded irises that look as though the buds wilted. I pruned the wilted ones back. The others are fine. What’s going on?

We have had a very wet winter and spring. When there is lots of rain accompanied by the high humidity we also have had, the chances of bacterial infection increase. Since you indicated that it is only affecting the bud end and that the end at the rhizome looks healthy when you cut off the stalk in question, most likely the buds gathered water and, without our usual low humidity to dry the moisture, a bacteria or even a fugal spore got in there.

You have done the right thing, which is to remove the dead stalks. After the irises have finished blooming, be sure to remove any dead leaves. Check to see if your rhizomes need thinning and also check if there is any overhang from larger, background shrubs or trees.

Should next winter and spring be another wet one like this one with few days of low humidity, you may want to go out and prune away some of the overhang to increase good air circulation.

Remember, this has been a particularly wet spring with high humidity. Bearded irises have few problems and require little fussing. They do, though, need to be thinned about every three years.

Q: We have an ornamental plum in our yard, one of the red-leaved ones. In the summer it drops a large quantity of small red fruit on the lawn. Is there a way to prevent this tree from forming fruit?

Yes. One way is with a growth regulator spray that contains ethephon. It works through contact (as opposed to something systemic). The application period is during the flowering season when it is in mid- to full bloom, usually February into March for these trees. The challenge is timing, getting the chemical on the blooms for maximum effect.

Another way is with pruning. The flowers form on one-year old shoots (last year’s growth) and this is where the fruit will develop. If you prune out some of this year’s growth, you will reduce the lateral branches on which buds and fruit form. By doing this, though, you also will reduce the flowery display of blossoms.

A third option would be to remove this tree (especially if it is at the end of its life expectancy) and replace it with something more desirable, either a tree with edible fruit or a shade tree.

Q: Village Harvest volunteers just harvested a big crop of oranges in Davis. After we started picking them we noticed that the tree has a heavy white fly infestation. Will these oranges be safe to eat? Could we spread the problem to other gardens?

The Garden Doctor would like to recognize Village Harvest (, which is helping increase food security, especially for needy families in Yolo County. Their website reports 24,331 pounds of fruit harvested already in 2011!

White flies are a problem with citrus trees like oranges because they are sap suckers, which cause leaf wilt and drop, and also because they excrete honeydew, which attracts ants and promotes the growth of sooty mold. White flies rise up in clouds when the tree is disturbed.

Eating the fruit is harmless; the mold on the oranges should wash off. White flies can infect other gardens via contaminated foliage, but shouldn’t be a problem on the fruit or ladders and other equipment. You can read more about these pests and others at

Q: We just bought a home in a fairly new development in Davis. We have trees in the front yard and don’t know what they are or how to care for them. Is there a good way to identify trees?

Trees can be identified in several ways, often by leaf style and fruit. Also, look around your neighborhood and notice if there are other yards with trees like yours and ask your neighbors. You can always bring a leaf sample and, hopefully, a flower sample in a plastic bag to the Master Gardener table at the Saturday Davis Farmers Market and the gardeners there can identify the tree.

You could also take a photograph of the mystery tree(s) and email it to the Master Gardener website at

If you really enjoy this detective work, you could also look at the city’s web page,, which has a list of trees recommended for planting as street trees, and a link to the organization Tree Davis.


Finally, here’s a thought for Mother’s Day gardeners (the title of an interesting essay by Andrea O’Reilly): “In searching for my mother’s garden, I found my own.” Have a wonderful day in your garden.

— Submit questions, addressed to the “Garden Doctor,” by email to [email protected], voice mail to (530) 666-8737 or regular mail to UCCE Master Gardeners, 70 N. Cottonwood St., Woodland, CA 95695. Be sure to include your contact information, because any questions not answered in the Garden Doctor column will be answered with a phone call or email to you.



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