Plants that grow under an oak tree must be able to withstand drought. Oak trees require little to no water during the summer months. An oak tree that is allowed to be wet will eventually develop crown rot, root rot and oak root rot, which will inevitably kill the tree. All plants should be planted 10 feet away from the trunk of the oak tree and only drought-tolerant species should be considered.
A lovely biannual that self seeds with very little problem. The hollyhock is exceptionally drought resistant. They grow with virtually no care. Flowers can be white, red, pink, salmon and even a rare black color. The plants can tower 6 feet in height with spears of blossoms.
Yarrow plants grow 3 feet in height. The plant is a hardy perennial that enjoys full sun and is very drought tolerant. The University of California suggests planting yarrow under oak trees and then simply mowing to grass level after blooming. The plant produces fern-like foliage with large flower heads that can be either white, pink or red.
There are close to 50 varieties of the yucca. The perennial is a member of the Agave family. It grows long spear-like evergreen foliage and large spikes of white bell like flowers. The yucca is extremely drought tolerant and heat resistant. Bees adore the flower heads. Plant at least 10 feet out from the trunk of the oak.
The California poppy grows to a height of around 18 inches. The plants features brilliant orange papery blossoms that open during the day and close at night or in windy conditions. Specialty colors of pink, yellow and red can also be purchased from a select few nurseries. The California poppy self seeds with ease and withstands extreme drought situations. It is a perennial.
Monkey flowers thrive around oak trees. They can withstand partly shady conditions and extreme drought. Monkey flowers are commonly called Diplacus. They come in red, yellow, orange and purple.
The evergreen currant can make an ideal ground cover under an oak tree. The University Of California considers it to be the best ground cover to be planted under an oak tree because of its ability to survive dry and shady conditions. Evergreen currants grow to a height of approximately 2 feet but one plant can easily spread 8 feet. The foliage is extremely fragrant.