No olive trees will survive the Denver’s winters. Because of this, olive trees in Denver must be grown as potted trees. By growing them in pots, you can move them outside as a summer and early fall ornamental but bring them inside for the winter. As potted trees, however, a number of different varieties will grow in the Denver area.
Different varieties of olives have different tolerances for cold. Some varieties will only tolerate temperatures down to 35 degrees F. Because of the risk of sudden freezes that were not forecast, these olives are more risky as potted trees in Denver. Fruitless olive trees that grow well in containers in Denver include Majestic Beauty and Little Ollie. Fruiting olive trees that grow well are the Arbequina and the Picholine. The Arbequina is hardy down to United States Department of Agriculture (USDA) hardiness zone 7. The Picholine is hardy to USDA hardiness zone 8. Although these trees can tolerate some temperatures that are below freezing, bringing them in when frosts are forecast can help reduce the risk of winter injury in Denver.
Olive trees generally do well in pots. Although they will not grow as large as those planted in their native growth range, you can encourage larger ornamental potted olive trees by planting your olive tree in a larger pot. If you want a smaller tree, plant your tree in a smaller pot and remove it for root pruning every 1 to 2 years.
Olive trees will do well in loamy potting soil. However, make sure your potting soil drains well. If it does not, add some sand to help encourage drainage. Because the soil will eventually lose some nutrients, fertilize the tree with a high-nitrogen fertilizer. Follow package directions for green plant growth.
Sun and Water
Your potted olive tree in Denver can tolerate full sun or partial shade. If growing in the full sun, be sure to water your tree frequently. The combination of higher altitude sun and dry air can cause potted plants to dry out more quickly. When watering, do not water until it is soaking wet. Allow the tree to dry out between waterings.
Olives need a period of dormancy. In the winter, bring your olive indoors, but keep it away from heaters and furnaces. However, it will still need light. Keep the tree in a west or south facing window. How cold the winter location for the tree can be will depend on the variety of tree.