Horticulture Guy"Live Long and Garden" – Peter Punzi

Q. In one of your answers: Shinseiki Asian pear is “considered nearly completely self pollinated” Does it mean there is no need another pollinator? Lisa- from New York

A.  A little background – most fruit trees have a built in mechanism to prevent self fertilization – presumably because self fertilization similar to inbreeding reduces the vigor of future offspring and limits their gene pool.  This mechanism is not completely on or off but varies. So for example one tree may self pollinate 80% of the time and would be considered “nearly completely self pollinating”.  Another may only self pollinate 20% of the time and would be listed as requiring a suitable pollinator.  You may improve the “nearly completely” pollination with a suitable plant (usually shown on a pollination chart) and presumably get close to the additional 20% pollination.  The pollination chart takes into account the time of bloom (since bees don’t as a general rule pollinate with long term storage pollen) and how closely related the plants are.  Usually if trees share parents the self fertilization prevention mechanism can reduce pollination.  To answer your question – yes you do not require an additional tree for pollination – although pollination could be improved.  If you find that you need to thin fruit each year anyway I would say you do not need an additional pollinator tree.

Q. I live in San Diego, California and I am wondering when the best time to prune an Asian Pear Tree (fruitless). It has tons of white flowers now, but once the flowers are gone we would like to shape it because it has several branches extending out. What is the best month to prune this tree in Southern Calif.? Thank you! Cristy

A. Ideally Asian Pears and other stone fruit are pruned during the dormant season. But this doesn’t mean it can’t be done at other times. Pruning can be done during the growing season to remove injured or diseased branches, or in your case to do some shaping.

Here is some info from your extension down at the University of California that I think you might find useful as you care for your Asian Pears:

Apples and Pears: Calendar of Operations for Home Gardeners
Fruit Trees: Training and Pruning Deciduous Trees

Q. I have a huge, beautiful fruitless plum tree. I’ve never pruned it but it’s time. When is it a good time to prune it? Thank you! Cher – Burbank, California

A. The time to prune it is after it finishes blooming in the spring.

Q. How tall will Prunus Caroliniana ‘bright and tight’ grow?  Will these shrubs grow as vigorously in a wine barrel container? Jamie Jameson – Monterey, CA

A. The Carolina Laurel Cherry is an evergreen tree/shrub that is native to the east coast from North Carolina over to Texas. This variety has a more compact habit than the species as the cultivar name suggests.  In the size container you suggest they probably will top out at 10 feet tall.  If they were grown in the ground they may reach 20 feet (The species can get as large as 40 feet tall).  I am sure you can grow them in California in pots but here in the Puget Sound region you would need to protect the plants during the winter.  These trees are rated to USDA Hardiness Zone 8, which would overwinter here in the ground.  When grown in containers I usually suggest buffering 2 zones.  So here in our Zone 8 areas I would suggest growing Zone 6 plants in containers when they are not protected during the winter.  Protection could be as simple as moving them to an unheated garage or in a protected area near the house.

Q. I have a rhododendron. Dark green upon planting. Western exposure. Leaves and new growth turn pale green and droop. Tries to set buds and flower but buds do not mature and flowers are extremely small and die back quickly upon opening. Paul Faro – San Leandro CA

A.  Sounds to me like you have a fungal root rot disease (Phytophthora spp.).  Although pale leaves could be caused by improper pH/nutrient problems, the drooping and die back sound more like this disease, which is encouraged by poorly drained soils and planting deeper than it was in the container.  Root rot disease is tricky to diagnose since the symptoms can be confused with cultural problems like low pH/nutrient problems (pH should be between 5.5 and 5.6 to allow minerals like iron and magnesium to be absorbed) which would result in pale green leaves or drought which would cause drooping and difficulty in absorbing nutrients.  The way you presented the symptoms makes me thing it is more likely root rot disease.  This is not easy to treat with fungicides and you may be faced with replacing the shrub.  Rhododendrons are not the only species vulnerable to this disease so you will need to ask for a resistant variety of Rhododendron or a species of shrub that is not susceptible. You may be able to bring a sample to your local County Extension for accurate diagnosis and also to find out what a suitable replacement shrub may be for your area.