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Japanese maples do best out of the heat

One of the most popular decorative landscape trees is the Japanese maple (acer palmatum). Native to Japan, Korea, Taiwan and eastern China, there are more than 1,000 known cultivated varieties. More than 300 can be easily found, many of them in local nurseries throughout the year.

There are two main types of Japanese maples: the standard palmatum which can reach 50 feet in height, but is more commonly found at 25-30 feet tall in cultivation; and the laceleaf type, palmatum dissectum, which is considered to reach 10-12 feet at maturity. Both are worthy specimens in the garden and contribute more than just size to the landscape. There are so many points of interest to these trees that it's hard to list all of their interesting or unusual characteristics.

Cultivated for hundreds of years in Japan, Japanese maples have been popular since the 19th century in the United States. Many parts of the Pacific Northwest have a climate that is very similar to the one found in Japan and the trees thrive in the cool temperatures and high humidity found in the region.

As you are well aware, we have a variation of that climate in the Medford area. Our summers can be brutally hot and dry compared to many parts of the Northwest. This dictates some care in locating the trees when planting. Let's look at the critical needs of these trees that we must meet in order to have success growing them.

The most critical factor in determining where to plant your Japanese maple is the amount of direct sun it will receive during the summer months.

Limiting exposure to the morning hours is ideal. Although I have seen some trees thriving in nearly full sun, those specimens are the exception, rather than the rule. In fact, the best stand of mature maples in Medford, of which I am aware, was started in the shade on the north side of a two-story house. This home also features the best laceleaf I have seen outside of Lithia Park.

There seems to be ample depth of a reasonably fertile soil to allow the growth of a large root system. The trees have received regular irrigation since they were planted. There is no lawn to provide competition.

Sunscald of the trunk and the branches is likely to occur to a Japanese maple that is placed in a spot that is too hot for it, or does not receive adequate watering during the summer. The trees cannot tolerate any reflected heat with our low summer humidity.

Leaf scorch is almost guaranteed to occur to any foliage that is exposed to drying winds or the reflected heat from roofs. I have seen many Japanese maples planted in the shade and protection of large roof overhangs at entryways that look fabulous until the foliage clears the roofline and begins to fry in the hot afternoon sun. Avoid this problem with the careful selection of the proper cultivar that will stay lower than the roof.

Many years ago, when I was just learning my craft, a man who taught me much about the way of plants told me that the proper way to prune Japanese maples was to forego the use of shears, loppers or saws and only use bare hands to snap out dead twigs. This might seem a bit extreme, but the point of the story is that Japanese maples should have their growth directed while the branch is still small and not to wait until one has to correct structural problems with a saw. By that time, much damage can result from extreme pruning.

Japanese maples are beautiful trees that grow quite easily once you have found the proper site for them. As the man said, there are three things you need to know to grow them well: location, location and location.

Stan Mapolski, aka The Rogue Gardener, can be heard from 9-11 a.m. Sunday mornings on KMED 1440 AM and seen in periodic gardening segments for KTVL Channel 10 News. Reach him at stanmapolski@yahoo.com.

Cultivar characteristics

Some of the distinguishing features of different cultivars ( a cultivated variety of a plant that is unique to others of its species) are as follows:

  • Leaf shape and size: shallow or deeply lobed; palmately compound.
  • Leaf color: from the lightest greens through reds and purples; variegated varieties with white or pink edges.
  • Bark and twig color: some getting brighter in winter.
  • Fall color: leaf color intensifying to fiery shades of red and orange.
  • Color and shape of samaras (the winged seedpods; "helicopters").
  • Range of growth forms and sizes: plants from 2-foot-tall mounds to inverted vase shapes to rounded shade trees.