Ask Mr. Smarty Plants

"Magenta maple" is apparently a trade name given to either a cultivar or selection of Acer rubrum (red maple), although we could find no information on that particular named species.  The first thing we want to observe is that Acer rubrum is not native to Calfornia, but rather the eastern part of the United States. The closest to California that it is native is eastern Texas and Oklahoma. This is because it likes the moist soils along streambanks and in woodlands, and a slightly acidic soil. We don't know exactly that your soil is, but we can tell you that most of the soils in the western portion of the United States, including Central and West Texas, are alkaline. 

If a tree on one side of your property is doing well and a tree of the same species on the other side is doing poorly, you need to examine what has changed in the environment around the second tree that might be causing it to decline.  Did you have any indications of insect activity around the trees before you sprayed them with insecticide? Often disease and insects will attack a plant already under stress for some other reason, but if there is no insect activity it's really better not to apply insecticides. A native tree also shouldn't need fertilizer. If it is in the right kind of soil, it is getting the nutrients and trace elements it needs from the soil. Fertilizer should never be applied to a tree under stress. 

Back to the environment of each tree. The red maple has high water use, and likes sun (6 hours or more of sun a day) or part shade (2 to 6 hours of sun.) Is the tree that is not doing well getting the same amount of water as the other, or is it on a slope or in sandy soil where the artificial irrigation or rain just drains away?  Is it heavily shaded by a larger tree or a building? Has there been any compaction of soil around the sick tree, as with building materials piled on it, or vehicles parked beneath it? There is even some possibility of the roots of the ailing tree were potbound when it was planted, and if none of the wrapped-around roots were clipped, it could be rootbound and strangling. 

The Lady Bird Johnson Wildflower Center is committed to the use, care and propagation of plants native not only to North America but to the area in which the plant is being grown. Acer rubrum (red maple) is considered hardy from Zone 3 to Zone 8, and probably originated in the northern part of that range. Unless the tree is on a stream or in very moist soil, it should be planted north of Zone 9. Sacramento County is in Zone 9b, having an average annual minimum temperature of 25 to 30 deg. F. Zone 3 has average annual minimum temperatures of -35 to -30 deg. F. We are of the opinion that the red maple is planted in an area too hot and dry for it. However, there may be other causes that we cannot diagnose nor recommend treatment for at this distance. Contact the University of California Cooperative Extension Office for Sacramento County for closer-to-home assistance.

Acer rubrum

Acer rubrum

Acer rubrum

Acer rubrum