Oaks are magnificent shade trees. They have distinctive leaf and growth forms. The fruits are acorns, which are highly attractive to wildlife. Several selections do well in our soils and climate. They are a little more expensive to buy, but rarely are they disappointing. The following kinds are all large shade trees with a mature height of 50 to 70 feet.
The bur oak crown is rounded with an open form. This is a very rugged tree. It is tolerant of a wide range of soil types and air pollutants. The leaves are very dark green and glossy. It has very unusual branching characteristics with ridged twigs. The branching is excellent for winter interest. The fall foliage is yellowish brown. The growth rate is slow to moderate.
English oaks have a broad shape with a rounded top. They are tolerant of heavy clay soils. The branches grow out almost horizontally casting a dense shade. English oaks have a moderate grow rate once established. The fall foliage is yellowish-brown.
Northern red oak is a faster growing oak with broad spreading branches and a round crown. It may have some problems with iron chlorosis, which causes yellow foliage. This happens frequently when they are planted in very alkaline soils. A soil with a pH of less than 7.5 is recommended. The fall foliage is spectacular with leaves turning dark red, then ruddy brown and orange.
Swamp white oak is a rugged, hardy tree with a broad oval crown. Their growth rate issimilar to English oak. They tolerate clay soils. The foliage is dark green with a silvery underside, and fall foliage is a reddish-bronze.
Pin oak is not recommended for most sites in Colorado because it is very susceptible to iron chlorosis.
Gambel oak isnative to Colorado and is adapted to most soil conditions in our state. Unlike the ones previously mentioned, its typical form is a multi-stemmed shrub but can become tree-like withadditional water.
Oaks are generally pest free. Galls, or round protrusions on leaves or stems, are unsightly but do not harm the trees. No control measures are recommended.
For more information, see the following Colorado State University Extension fact sheet(s).
- Insect and Mite Galls
- Xeriscaping: Trees and Shrubs
- Choosing a Soil Amendment
- Small Deciduous Trees
- Large Deciduous Trees