Heat
Sequoia trees obtain the moisture they need from several sources, including high amounts of rain and the fog that frequents the area. The soil in which the trees grow often retains moisture to help the trees when the weather is dry. However, in the hot summer months, the air may become drier and temperatures rise, causing the trees to suffer from a lack of moisture. When this happens, some of the needles on the tree may dry out and turn orange.
Disease
Some sequoia trees become infected with a disease that turns the needles orange. One of the most common diseases to affect a sequoia tree is called phomopsis blight. With this disease, the sequoia needles turn orange, especially near the bottom of the tree and among the newer growth. This disease is caused by the fungus Phomopsis juniperova and is typically a problem when foliage is wet. Removing the diseased areas of the tree and treating it with chemicals helps cure the disease and prevent re-infestation in the future.
Fall
Even though the sequoia trees have needles, they are considered deciduous trees because they lose those needles in the fall and winter. As the weather turns colder, the needles begin to turn orange. Once they turn orange, they fall to the ground, just as the leaves of other deciduous trees do. The dawn redwood is most well known for losing its needles, though those trees that are planted closer together typically only lose the needles from the lower branches.
About Sequoias
Sequoia trees are known to be the tallest trees in the world. They are most commonly found in California, but some smaller species can be found on the East Coast as well. Each of the three main types of sequoia trees have their own types of needles. For instance, the needles of the coast redwood are much bigger and flatter than those of the other types of sequoias. The overall shape of each tree is also different, from the flared base of the giant sequoia to the conical shape of the dawn redwood to the sparse look of the coast redwood.