Garden Doctor: Japanese maples are worth the extra work

Question: I see Japanese maples growing around town. Some seem fine and others seem to be suffering. What’s the secret? Is the Davis water’s boron at fault again?

Answer: The Garden Doctor has a keen fondness for Japanese maples. These small shrubs or trees rarely get taller than 25 to 30 feet; many are much smaller, have beautiful shapes, sizes, colors of foliage, twigs and bark. They are multi-stemmed, and prefer a north or east exposure, possibly sheltered away from drying north winds. A few days of hot, north wind or prolonged days of 100-degree heat take a heavy toll on these delicate beauties.

A thick layer of mulch around the roots helps to maintain maximum hydration. Only a few thrive in the hot afternoon; summer sun and salt build-up (boron) can be an issue.

The boron issue can be somewhat remedied by flooding occasionally to leach out salts. Burned edges on the leaves are sure signs of salt build-up and from the Doctor’s experience often occur in small pots. Dissectum type maples (lace leaf maples with deeply divided and dissected leaves) are more susceptible to boron burn than broader-leafed specimens.

The Doctor has a source of non-boron water and has been successful in growing healthy maples in pots using this water. The beauty of these Japanese maples is so appealing the Garden Doctor cheerfully accepts the additional labor involved. The new “Sunset Western Garden Book” has an excellent section on Japanese maples with detailed descriptions of many varieties.

Q: I have found two peculiar things in my yard. One is brown and seems to have attached itself to the side of a pot and the other is on my lawn, yellowish, looking like something regurgitated. Is either anything I need to be concerned about as far as destroying my garden?

A: What you have described is slime mold. The yellowish substance is referred to as dog vomit slime mold for obvious reasons. Slime molds are interesting substances. They are not true molds or fungi, but rather very primitive, single-cell organisms. They pose no threat to humans or plants.

People often refer to them as mold or fungi because they grow in the same type of environment — warm, wet conditions where there is decaying material and bacteria to feed upon. On lawns, the gooey substance may suffocate the grass. You can rake the slime mold or blast it with a stream of water. Mowing also will remove it. On its own, it disappears within about a week after it has dried and becomes a dusty substance.

There are more than 900 species of slime mold worldwide and they are found in a wide variety of colors from off-white to orange to brown to brick red. In urban areas, one is most likely to find them in mulched areas. Most of the time they spread out as on lawns, but when there is no room to spread or food supply is sparse, these single-cell organisms will congregate. Check out the IPM website for pictures at http://www.ipm.ucdavid.edu/PMG/PESTNOTES/pn74100.html.

Speaking of “peculiar”: the Garden Doctor was surprised when digging out an old rose bush to find, just below the soil surface, a hard object attached to the base of the bush.

It was nearly the size of a grapefruit, and varied in color from off white to brown. A quick search on Google identified the mystery as “crown gall disease,” caused by the bacterium Agrobacterium tumefaciens. The source for this information was a Cooperative Extension publication from Oklahoma State University on rose diseases that included a photograph of a gall very like the one dug up in Davis. The advice from OSU would be well taken for any rose transplanting situation:

1. Transplant only disease-free plants;

2. Avoid wounding during transplanting;

3. Remove infected plants as soon as galls are observed, along with all soil in and adjacent to the root system;

4. Take care to avoid injuring roots or crown area when transplanting roses; and

5. Disinfect pruning and cutting tools frequently with a 10 percent dilution of household bleach.

In the case of the old rose, it was destined for the trash. Master Gardeners, including the Garden Doctor, have confidence in advice from Cooperative Extension sources, both in California and in other states, because they are research-based and subject to peer review.

— Send questions, addressed to the “Garden Doctor,” by email to mgyolo@ucdavis.edu, voice mail to 530-666-8737 or regular mail to UCCE Master Gardeners, 70 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.

You can request the Yolo Gardener newsletter delivered by email and learn more about the Master Gardener program in Yolo County at http://ceyolo.ucdavis.edu/Gardening_and_Master_Gardening.