Caring for, Pruning and Fertilizing an Oak Tree Landscape
With their round shapes and leafy branches, oak trees (Quercus spp.) are robust landscape plants. Evergreen oak trees provide year-round color to a garden, while deciduous oak trees provide shade during sunny summers. Many are hardy to Mediterranean climates, such as the live oak (Q. virginiana) that's hardy to U.S. Department of Agriculture plant hardiness zones 8 through 10, and the English oak (Q. robur), hardy to USDA zones 6 through 9. In the wild, vegetation often grows beneath oak trees during wet winters but dies out by summertime, creating an oak-dotted landscape of crisp golden vegetation and grass. Because oak trees are generally low-maintenance plants, you can easily mimic this in your home garden.
Oak trees prefer full sun and well-drained soil. They enjoy a natural change of seasons, with dry summers and moist winters. As long as you experience winter rainfall, you don't need to water oak trees in winter. To make up for a dry winter, you can give oak trees a thorough soaking in the spring. It's also safe to water them once or twice during dry summers. These infrequent waterings should consist of gradual releases of water all day, to thoroughly soak the soil without making it waterlogged. You should never water oak trees more than once a month.
When planting other plants around oak trees, you should select only drought-tolerant plants that don't require summer watering. It's best to space them at least 6 feet from the base of each oak tree, to give the oaks breathing room. It's also appropriate to lay 2 to 3 inches of mulch around the base of each oak tree to keep the soil from drying out and prevent weeds from growing that would steal nutrients from the tree.
When to Prune
Like many other deciduous landscape trees, deciduous oak trees need regular pruning; evergreen oaks prefer to grow without it. The safest time to prune them is during the dormant period in winter, as this sparks new growth for the blooming season and allows wounds to heal as warm spring weather hits. Though light trims in spring and autumn won't hurt oak trees, it's vital that you refrain from pruning them in March through July, as this is when small beetles can transmit oak wilt, a fungal disease that discolors the leaves and eventually kills oaks.
Reasons for Pruning
An annual trim can benefit deciduous oaks. You can prune to control size and remove diseased branches, but it's smart to remember that pruning slows growth while sparking bud development. The only reason to completely remove a branch is to get rid of a dead or diseased limb; otherwise, removing branches unnecessarily exposes the interior of the tree to sun, which can lead to damage. You should always leave the branch collar, which is the swelled area at the trunk where the branch begins to emerge, rather than make a flush cut that will permanently put a stop to growth there.
Young trees need fertilizer to grow, while mature oaks need fertilizer to maintain health. You should fertilize in the spring, late summer or autumn, when rainfall will help wash the nutrients through the soil to reach all parts of the root system. Though you can apply a balanced fertilizer with nitrogen, phosphorus and potassium, it's also safe to fertilize with a nitrogen-based fertilizer -- the type that the surrounding lawn may also appreciate. You can also let the leaves that fall from deciduous oaks remain on the ground, as they saturate the soil with nutrients as they decompose.
- Iowa State University Forestry Extension: Pruning Young Landscape Trees
- New Mexico State University: Fertilizing Oaks
- University of California Cooperative Extension: Pruning Oak Trees in Southern California
- North Carolina State University: Recommended Trees for Urban Landscapes: Proven Performers for Difficult Sites