Sonoma County Tree of the Week: Douglas Fir (Pseudotsuga menziesii)
Last week we took a look at the Coast Redwood tree, this week we will continue our exploration of the giant trees of the West by looking at the Douglas Fir, Pseudotsuga menziesii. If you see a tree in Sonoma County that is over 60 feet tall, in all likelihood you have seen either a Douglas Fir or a Coast Redwood. Though the tallest recorded standing tree in the world is the Redwood at 380 feet, there are reports of Douglas Fir trees of the past reaching in excess of 400 feet!
Much like the Redwood, the Douglas Fir has been an enormously important lumber source. It’s fast growth rate, strength, and flexibility contribute to it being used in all types of construction domestically and abroad. If you go to a hardwood store to pick up some 2x4s you’re most likely going to be getting Douglas Fir.
These Douglas Firs that we know of here in Sonoma County are known as Coast Douglas Firs, as opposed to the two other varieties known as the Rocky Mountain Douglas Fir and the Mexican Douglas Fir. The Coast Douglas Fir grows from British Columbia down to as far South as Santa Barbara. It can be found in many of our local parks living amongst Redwoods, oaks, and other conifers. Ragle Ranch, Annadel, and Shiloh are just a few of the local parks that host this beautiful tree.
Typical Maintenance
- Reduction of overextended limbs–limbs can get very long and heavy and it is not uncommon for them to break. Making minor reductions to the length of these limbs can have a large impact on their strength, and reduce the likelihood of broken limbs during wind events.
- Removal of co-dominant tops.
- Removal of deadwood.
- Clearance pruning.
Preferred living environment:
Irrigation and soil: The Douglas fir prefers deep, well draining, slightly acidic soils. Once established, if the Douglas Fir is noncompacted well draining soil it doesn’t need much water. But prolonged drought will negatively affect the Douglas Fir especially if soil conditions are not ideal. In an urban environment, if a Douglas Fir is showing any signs of stress I would recommend a deep watering every 3-4 weeks during the heat of summer.
Planting site: The Douglas fir enjoys full sun to partial shade. Give the Douglas Fir lots of space away from any structures–it grows fast, is sensitive to root disturbances, and it is common for it to drop dead limbs.
Pests/diseases
Lots of Douglas Firs are suffering–drought and fire damage have stressed many of these trees which makes them more susceptible to pests and diseases. The Douglas Fir Beetle is the most damaging pest and can very quickly kill a tree that is already stressed. Other pests and diseases include:
- Weevils
- Wood borers
- Root rots
- Needle cast fungi
The best thing to do with all trees, but especially trees like the Douglas fir who have aggressive opportunistic pests, is to provide proper care for the trees before any of these issues show up. Make sure the soil under the tree isn’t being disturbed by construction or heavy traffic, provide additional irrigation during periods of drought, and have the tree inspected/pruned by an arborist every few years.