The Hows and Whys of Planting Fruit Trees on a Slope

UW intern, Taylor Thao, contributed research for this blog:

 

We often imagine orchards as flat spaces with rows of trees, but not all spaces are flat. While some worry that a slope can affect the stability of the tree or be impacted by erosion, a gentle or moderate slope may actually be beneficial and could be more resilient in future climates. Why?

• Planting fruit trees on a gently sloped site allows cold air to drain away and will lessen frost and freeze damage to flowering blossoms and buds in spring and frost damage in fall. 

• Fruit trees on slopes allow cold air to drain to lower levels creating a more breathable environment that is great for hotter temperatures.

• The sloping ground can help the soil to become well-drained, promoting tree growth with proper precautions 

Drawing of what is called "Biological Terracing" from The Holistic Orchard

Slope direction can impact the sunlight exposure the trees may receive and the different temperature characteristics of the site. In general, Northern and Eastern-facing slopes are typically cooler and can result in a delay in the ripening of fall-harvested fruits. On the other hand, South facing slopes tend to warm up faster in the spring compared to North-facing slopes. While North-facing slopes are better for fruit trees that flower earlier, they receive less sun until late spring/summer, and in Seattle’s colder, wet springs planting on a North slope may not give plants enough sunlight and heat to flower and fruit. 

When possible, planting on South-facing slopes is better for our environment. South-facing slopes receive more light and heat from the sun; plant growth increases and crops will ripen earlier. Westward-facing fruit trees may be at risk of sunscalding and wilting in summer because of how many hours of sun we get during these months. 

 

The placement of the trees on the slope is also important to consider, plantings nearer the top of a slope are better and will usually suffer less spring frost injury than those at the bottom of the slope. 

Slope at McAuliffe Park in Kirkland that gets ample sunlight

Fruit trees are adaptable to most soil as long as it’s not too heavy or rocky. Future climate reports suggest that we will have an increase in extreme heat, with longer and hotter heat waves and on occasion, colder winters with extreme frost. Both of these situations can stress out and damage your fruit tree. 

You can see examples of sloped orchards at High Point, Troll’s Knoll, and McAuliffe Park, where City Fruit planted fruit trees and bushes this past Feb and March. Because a part of the slope at Troll’s Knoll was steep, we added a leveled berm of soil and branches to help with erosion and also to provide a stable walk path to access the trees. P-Patch gardeners intend to add in pavers along the top of the walk path once the branches have decomposed and the berm settles. At McAuliffe, a future walk path may be added once the trees and berries have started to fruit in the coming years, and at High Point, the berries were planted at the bottom of the slope and beside an existing path for easy access!

Our now-completed berm at Trolls Knoll Park!
City Fruit staff and two UCLA students posing with a newly planted plum tree at McAuliffe Park
City Fruit staff planting berry bushes on the slope of High Point's Pond Park

To learn more about our orchard planting projects, contact Riley at riley@cityfruit.org.